Meteorology and Weather Services
The Atmosphere
The primary cause of all the Earth's weather is the variation in solar radiation received at the surface. When the surface is warmed by the sun, the air next to it is, in turn, heated and it expands. This creates a low pressure area where the air rises and, at altitude, expands outward. Air from regions of relatively high pressure descends and then moves away from the center of the high toward the lower pressure areas. On both a global and local scale, this movement of air sets off an immensely complex process that generates all the Earth's weather.
Another major influence in the pattern of the weather is a phenomenon known as Coriolis effect. This is an apparent force, caused by the Earth's rotation, acting on any movement of air. If the Earth did not rotate, air would move directly from areas of high pressure to areas of low pressure. Coriolis force bends the track of the air over the ground to right in the northern hemisphere and to the left in the southern hemisphere. Viewed from above (as on a weather map) this makes air rotate clockwise around high pressure areas in the northern hemisphere and counterclockwise around lows. In the southern hemisphere, the rotation around highs and lows is just the opposite. In the northern hemisphere, the rotation of air around a low pressure area is called a cyclone and that around a high is called an anticyclone.
The strength of the Coriolis force is determined by wind speed and the latitude. Coriolis has the least effect at the equator and the most at the poles. It is also reduced in effect when wind speed decreases. Air moving near the Earth's surface is slowed by friction. This reduces the Coriolis force. However, the gradient pressure causing the air to move remains the same. The reduced Coriolis allows air to spiral out away from the center of a high and in toward the center of a low, and at an angle to winds aloft which are out of the friction level.
If the Earth did not rotate, air would move from the poles to the equator at the surface and from the equator to the poles at altitude. Because the Earth does rotate, Coriolis force and the pressure gradients tend to form three bands of prevailing winds in each hemisphere. Weather systems tend to move from east to west in the subtropical regions on the "trade winds." In the mid latitudes, the prevailing westerlies move weather systems from west to east.
All air carrier flights take place in the two lowest levels of the atmosphere. These are the troposphere and the stratosphere. The troposphere starts at the surface and extends vertically to roughly 35,000 feet. The thickness of the troposphere varies with latitude, being thicker over the equator than over the poles and with the season of the year (thicker in the summer than in the winter). The stratosphere extends from the top of the troposphere to about 26 to 29 miles altitude. The main characteristic that distinguishes the troposphere from the stratosphere is the temperature lapse rate. In the troposphere, the temperature decreases with increasing altitude at an average rate of two degrees Celsius per one thousand feet of altitude. In the stratosphere, there is little or no change in temperature with altitude. In fact, in some regions the temperature increases with increasing altitude causing temperature inversions.
The thin boundary layer between the troposphere and the stratosphere is called the tropopause. The height of the tropopause is of great interest to the pilots of jet aircraft for two reasons. First, there is an abrupt change in the temperature lapse rate at the tropopause and that has a significant effect on jet engine performance. Second, maximum winds (the jet stream) and narrow zones of wind shear are found at the tropopause.
The jet stream is a few thousand feet thick and a few hundred miles wide. By arbitrary definition, it has wind speeds of fifty knots or greater. The highest wind speeds can be found on the polar side of the jet core. There may be two or more jet streams in existence at one time. The jet stream is always found at a vertical break in the tropopause where the tropical and polar tropopauses meet. In addition to the high speed horizontal winds, the jet stream contains a circular rotation with rising air on the tropical side and descending air on the polar side. Because of the rising air, cirrus clouds will sometimes form on the equatorial side of the jet.
Weather Systems
When air masses of different temperature or moisture content collide, they force air aloft along the area where they meet. An elongated line of low pressure is referred to as a trough.
A front is defined as the boundary between two different air masses. The formation of a front is called frontogenesis. When a front dissipates, the area experiences frontolysis. All fronts lie in troughs. This means that winds flow around a front more or less parallel to the front, and in a counterclockwise direction. As an aircraft flies toward a front in the northern hemisphere, the pilot will notice a decreasing pressure and a wind from the left of the aircraft. After passing through the front, the pilot will note a wind shift to the right and increasing air pressure.
A front is usually the boundary between air masses of different temperatures. If cold air is displacing warm air, it is called a cold front. When warm air displaces cold air, it is a warm front. The speed of movement of the front is determined by the winds aloft. A cold front will move at about the speed of the wind component perpendicular to the front just above the friction level. It is harder for warm air to displace cold air and so warm fronts move at about half the speed of cold fronts under the same wind conditions.
A stationary front is one with little or no movement. Stationary fronts or slow moving cold fronts can form frontal waves and low pressure areas. A small disturbance can cause a bend in the frontal line that induces a counterclockwise flow of air around a deepening low pressure area. The wave forms into a warm front followed by a cold front. The cold front can then overtake the warm front and force the warm air between the two aloft. This is called an occluded front or an occlusion.
Most fronts mark the line between two air masses of different temperature. However, this is not always the case. Sometimes, air masses with virtually the same temperatures will form a front. The only difference between the two is the moisture content. The front formed in such conditions is called a dew point front or a dry line.
The surface position of a front often marks the line where an arctic and a tropical air mass meet at the surface. The jet stream is located in the area where these air masses meet at the altitude of the tropopause. There is often a rough correlation between the surface position of a front and the location of the jet stream. Generally speaking, the jet stream will lie to the north of the surface position of a front. As a frontal wave forms, the jet will move toward the center of the deepening low pressure area. If an occluded front forms, the jet stream will often cross the front near the point of the occlusion.
Stability and Instability of Air
When a parcel of air is forced to rise it expands because its pressure decreases. Air that is forced to descend is compressed. When the pressure and volume change, so does the temperature. When air expands, it cools and when it is compressed, it warms. This cooling or heating is referred to as being adiabatic, meaning that no heat was removed from or added to the air.
When unsaturated air is forced to rise or descend it cools or heats at a rate of about 3°C per 1,000 feet of altitude change. This called the dry adiabatic rate. The saturated adiabatic rate is normally much lower.
When moist air is forced upward, the temperature and the dew point converge on each other at a rate of about 2.5°C per 1,000 feet. At the altitude where the dew point lapse rate and the dry adiabatic rate meet, cloud bases will form. Once the condensation starts taking place the adiabatic rate slows considerably because the process of condensation releases latent heat into the air and partially offsets the expansional cooling.
Saturated air flowing downward will also warm at less than the dry adiabatic rate because vaporization of water droplets uses heat. Once the air is no longer saturated it will heat at the normal dry rate. An example of this is the "katabatic wind" which becomes warmer and dryer as it flows downslope.
The adiabatic rate should not be confused with the actual (ambient) lapse rate. The actual lapse rate is the rate at which the air temperature varies with altitude when air is not being forced to rise or descend. The actual lapse averages about 2°C per 1,000 feet, but that is highly variable. When a parcel of air is forced to rise, the adiabatic rate may be different than the ambient rate.
When a parcel of air becomes colder (and more dense) than the air around it, it will tend to sink back toward its original altitude. If the parcel becomes warmer than the surrounding air, it will tend to rise convectively even though the original lifting force may have disappeared. If this happens, the air is said to be unstable. When a parcel of air resists convective movement through it, it is said to be stable.
The best indication of the stability or instability of an air mass is the ambient temperature lapse rate. If the temperature drops rapidly as the altitude increases, the air is unstable. If the temperature remains unchanged or decreases only slightly as altitude is increased, the air mass is stable. If the temperature actually increases as altitude increases, a temperature inversion exists. This is the most stable of weather conditions.
Fog and Rain
Fog is a surface-based cloud that always forms in stable air conditions. The three main types are radiation fog, advection fog and upslope fog.
Radiation fog occurs when there is a surface-based temperature inversion. On a clear, relatively calm night the surface rapidly cools by radiating heat into space. This in turn cools the air within a few hundred feet of the surface and leaves warmer air aloft. If the temperature drops to the dew point, fog will form. Since the minimum temperature during the day occurs just after sunrise, this type of fog often forms then. This fog will dissipate when the air warms up enough to raise the temperature above the dew point again. However, if the inversion persists, visibility can remain limited due to lingering fog and haze. Wind or any significant movement of air will disperse both radiation fog and haze.
Advection fog and upslope fog both require wind to form. Advection fog forms when warm moist air flows over a colder surface. The temperature of the air drops to the dew point and fog forms. This commonly occurs over bodies of water such as lakes or oceans. The fog can drift over land on the leeward (downwind) side of the body of water lowering visibility at nearby airports. If the wind increases to over about 15 knots, the fog will tend to lift into low stratus clouds.
Upslope fog forms when moist, stable air is gradually moved over higher ground by the wind. As the air rises, it cools adiabatically and fog forms. This type of fog is common in mountainous areas.
All clouds are composed of tiny droplets of water (or ice crystals). As these drops of water collide with each other, they form larger drops until they precipitate out as rain. As a general rule, clouds need to be at least 4,000 feet thick to produce precipitation reported as light or greater intensity.
Thunderstorms
Thunderstorms are always generated in very unstable conditions. Warm, moist air is forced upward either by heating from below or by frontal lifting, and becomes unstable. When the rising air cools to its dew point, a cumulus cloud forms. This "cumulus stage" is the first of three in a thunderstorm's life. It is characterized by a continuous updraft as the cloud builds. As the raindrops and ice pellets in the cloud grow larger, their weight begins to overpower the lifting force of the updrafts. As the drops fall through the cloud, they cool the air making it more dense than in the surrounding updrafts. This process causes downdrafts to form within the cloud.
When the downdrafts become strong enough to allow the first precipitation to reach the surface, the mature stage of the thunderstorm has begun. Eventually, the downdrafts cut off the updrafts and the storm loses the source of warm air that is its driving force. When the storm is characterized predominantly by downdrafts, it is in the dissipating stage.
Air mass thunderstorms are associated with local surface heating. On a clear, sunny day, local hot spots form that are capable of making the air over them unstable enough to generate a thunderstorm. Because the downdrafts in an air mass thunderstorm shut off the updrafts fairly quickly, this type of storm is relatively short-lived.
Steady-state thunderstorms are usually associated with weather systems. Fronts, converging winds and troughs aloft force upward motion. In a steady-state storm the precipitation falls outside the updraft allowing the storm to continue without abating for several hours.
The most violent type of steady-state thunderstorms are those generated by cold fronts or by squall lines. A squall line is a non-frontal instability line that often forms ahead of a fast moving cold front. Thunderstorms generated under these conditions are the most likely to develop cumulonimbus mamma clouds, funnel clouds and tornadoes. A severe thunderstorm is one which has surface winds of 50 knots or more, and/or has hail 3/4-inch or more in diameter.
Pressure usually falls rapidly with the approach of a thunderstorm, then rises sharply with onset of the first gust and arrival of the cold downdraft and heavy rain showers. As the storm passes on, the pressure returns to normal.
Even though thunderstorms are cumulus clouds formed in unstable air they can sometimes penetrate overlying bands of stratiform clouds. These are known as "embedded thunderstorms." Because these thunderstorms are obscured by other clouds and it is impossible for a pilot to visually detour around them, they present a particular hazard to IFR flight.
When they can, most pilots prefer to visually avoid thunderstorms by flying around them or, if they can maintain a high enough altitude, by flying over the storm. If you are going to fly over the top of a thunderstorm, a good rule of thumb to follow is that the cloud should be overflown by at least 1,000 feet for each 10 knots of wind speed. Radar is a very useful tool in thunderstorm avoidance, especially at night or in IFR weather. The radar displays an area of precipitation size rain drops as a bright spot on the screen. Since thunderstorms often contain large water drops, they usually show up on the radar screen. A dark area on the screen is one in which no precipitation drops are detected. Areas of clouds may or may not be displayed depending on the size of the drops that make up the clouds.
Wind Shear
Normally we think of changes in wind speed or direction as having an effect only on an aircraft's ground speed and track. However, when there is a very rapid shift in wind speed or direction there is a noticeable change in the aircraft's indicated airspeed as well.
In a situation where there is a sudden increase in headwind (or decrease in tailwind) the aircraft's momentum keeps it moving through space at the same ground speed as before. This means that the aircraft will be moving through the air faster than before and there will be an increase in its indicated airspeed. The aircraft will react to this increase by pitching up and by tending to climb (or descend more slowly). When there is a sudden increase in a tailwind (or decrease in the headwind), just the opposite occurs. There will be a loss of indicated airspeed accompanied by a tendency to pitch down and descend.
Wind shear is defined as any rapid change in wind direction or velocity. Often, there is little or no turbulence associated with wind shear. Severe wind shear is defined as a rapid change in wind direction or velocity causing airspeed changes greater than 15 knots or vertical speed changes greater than 500 feet per minute.
Wind shear may be associated with either a wind shift or a wind speed gradient at any level in the atmosphere. Three common generators of wind shear conditions are thunderstorms, temperature inversions and jet stream winds. Thunderstorms generate a very significant wind shear hazard for two reasons. The shear from thunderstorms is usually encountered close to the ground where there is little time or altitude to recover. The magnitude of the shear is often very severe, especially in situations involving microbursts, which we will discuss shortly. Wind shear can be encountered on all sides and directly under the thunderstorm cell. Often, in a low altitude temperature inversion the winds are very light but just above the inversion layer the wind is much stronger. When an aircraft either climbs or descends through the top of the inversion it can encounter significant wind shear because of the change in wind speed. A jet stream is a narrow "river" of wind where the speed can change a great deal over a very short distance. This is the very definition of wind shear.
Microbursts are a very localized, but very dangerous, wind shear condition. They can occur anywhere that convective weather conditions exist. This includes rains showers, virga and thunderstorms. It is believed that about five percent of thunderstorms produce a microburst.
A microburst is a very narrow downdraft of very high speed wind. The downdraft is typically a few hundred to 3,000 feet across with vertical speeds up to 6,000 feet per minute. When the downdraft approaches the surface, the wind flows outward from the core in all directions. Not only are these outflow winds very strong (up to 45 knots) but their effect is doubled when an aircraft flies through the shear. For example, a 45 knot headwind approaching the microburst will be a 45 knot tailwind flying out the other side -- a change of 90 knots. This is usually a short-lived phenomena, seldom lasting more than 15 minutes from the time the burst strikes the ground until it dissipates.
An aircraft approaching a microburst will first experience an increasing headwind as it encounters the outflow. The increasing headwind shear causes the indicated airspeed to increase and gives the aircraft a tendency to pitch up and climb. This increase in performance without an increase in power might induce an unwary pilot into reducing power to maintain airspeed and flight path. As the aircraft flies into the core of the microburst the headwind shifts to a downdraft. The sudden loss of headwind will cause indicated airspeed to drop and cause the aircraft to pitch down and descend. The strong downdraft increases the tendency to descend and the aircraft can quickly get into the situation of having low airspeed and a very high rate of descent. As the aircraft flies out the backside of the microburst, it encounters an increasing tailwind shear that further reduces indicated airspeed and performance.
There are some wind shear conditions that exceed the performance capability of typical air carrier aircraft. For this reason it is imperative that pilots avoid situations where severe wind shear is either reported or is likely to exist. At this time only a couple of airports in the United States have experimental Doppler radar units capable of detecting wind shear. Many airports have the less sophisticated Low-Level Wind Shear Alert System (LLWAS), which is used to alert pilots to the possibility of wind shear on or near the airport. This system consists of wind sensors located around the perimeter of the airport as well as a center field wind sensor. When there is a significant difference in speed or direction between any of these sensors and the center field sensor, the tower will broadcast the difference. A typical tower transmission would be:
"SOUTH BOUNDARY WIND ONE SIX ZERO AT TWO FIVE, WEST BOUNDARY WIND TWO FOUR ZERO AT THREE FIVE."
The greatest danger from a wind shear encounter at low altitude is that the aircraft will pick up such a high rate of descent that the pilots will be unable to stop it before hitting the ground. The technique to be used during a wind shear encounter essentially involves trading airspeed for altitude. The exact procedures vary from one aircraft to another but if an aircraft encounters severe wind shear, the pilot should maintain or increase the pitch attitude, increase power to the maximum available and accept lower than normal airspeed indications. If this does not arrest the descent, the pilot should continue to pitch up until the descent does stop or until "stick shaker" is encountered.
Frost and Ice
No person may dispatch or release an aircraft, continue to operate en route, or land when in the opinion of the pilot-in-command or aircraft dispatcher, icing conditions are expected or met that might adversely affect the safety of the flight. No person may takeoff when frost, snow or ice is adhering to the wings, control surfaces or propellers of the aircraft.
The equipment most commonly used for deicing and anti-icing airplanes on the ground is the truck-mounted mobile deicer/anti-icer. The two basic types of fluids used are Type 1 (unthickened) fluids and Type 2 (thickened) fluids. Type 1 fluids have a minimum 80% glycol content and a relatively low viscosity, except at very low temperatures. The viscosity of Type 1 fluids depends only on temperature. The holdover time is relatively short for Type 1 fluids. Type 2 fluids have a significantly higher holdover time. Type 2 fluids have a minimum glycol content of 50% with 45% to 50% water plus thickeners and inhibitors. Water decreases the freeze point. The freeze point should be no greater than 20°F below ambient or surface temperature, whichever is less.
There is a one-step process and a two-step process for deicing and anti-icing. The one-step process uses heated fluid to remove snow, ice and frost. The primary advantage of this process is that it is quick and uncomplicated. However, where large deposits of snow or ice must be flushed off, fluid usage will be greater than with the two-step process. The two-step process consists of separate deicing and anti-icing steps. A diluted fluid, usually heated, is used to deice and a more concentrated fluid (either 100% or diluted, depending on the weather), usually cold, is used to anti-ice. Type 1 or 2 fluids can be used for both steps, or Type 1 for step 1 and type 2 for step 2.
Two precautions to observe when using this equipment are:
1. Do not spray deice/anti-ice fluid at or into pitot inlets, TAT probes, or static ports; and
2. Apply deice/anti-ice fluid on pressure relief doors, lower door sills, and bottom edges of doors prior to closing for flight.
For ice to form on an aircraft in flight, two conditions must be met. There must be visible water in the form of rain, clouds or fog and the air temperature must be below freezing. In those conditions, the water droplets become "supercooled." Although their temperature is below freezing, they remain in a liquid state. When such an unstable water droplet strikes an exposed object, it freezes on impact. The type of ice that forms on an aircraft depends on the size of the water droplet. Clear ice forms when relatively large droplets strike the aircraft and spread as they freeze. Rime ice forms when small water droplets freeze instantly when they hit the aircraft. These small droplets can be found in low altitude stratus clouds.
Freezing rain always occurs in a temperature inversion. Rain falls from clouds where the temperature is warmer than freezing. As the rain drops fall into colder temperatures, they become supercooled and will form ice on any aircraft flying through them. Eventually, the water drops will freeze into ice pellets. Any encounter with ice pellets in flight indicates that there is freezing rain at a higher altitude.
Snow always forms in colder than freezing temperatures by the process of sublimation. This is when water goes straight from its vapor state into ice without ever being a liquid. Wet snow occurs when it falls to altitudes with above freezing temperatures and begins to melt.
Frost forms by the process of sublimation when the temperature of a collecting surface and the dew point are both below freezing. Frost will form on aircraft surfaces on clear, cold nights when the air is stable and there are light winds. Frost can form in flight when a cold-soaked aircraft descends into warm, moist air. This type of frost presents no hazard to flight.
Turbulence
Light chop causes slight, rapid and somewhat erratic bumpiness without appreciable changes in altitude or attitude. Light turbulence causes momentary slight erratic changes in altitude and/or attitude. Light chop causes rapid bumps or jolts without appreciable changes in aircraft altitude or attitude. Moderate turbulence is similar to light turbulence, but of greater intensity. Changes in altitude or attitude occur but the aircraft remains in positive control at all times. It usually causes variations in indicated airspeed. Severe turbulence causes large, abrupt changes in altitude or attitude. It usually causes large variations in indicated airspeed. The aircraft may be momentarily out of control. In extreme turbulence the aircraft is violently tossed about and is practically impossible to control. Extreme turbulence may cause structural damage.
Turbulence that occurs less than 1/3 of the time should be reported as occasional. Turbulence that occurs 1/3 to 2/3 of the time is intermittent. Turbulence that occurs more than 2/3 of the time is continuous. High altitude turbulence (normally above 15,000 feet MSL) not associated with cumuliform cloudiness should be reported as CAT (Clear Air Turbulence).
Strong winds across mountain crests can cause turbulence for 100 or more miles downwind of the mountains and to altitudes as high as 5,000 feet above the tropopause. If there is enough moisture in the air, a mountain wave can be marked by standing lenticular clouds. These clouds mark the crest of each wave. Under the right conditions, several lenticulars can form one above another. A rotor current forms below the crest of a mountain wave. This is sometimes marked by a rotor cloud which will be the lowest of a group of stationary clouds.
The jet stream is a common source of CAT. The strong winds and steep wind gradients will almost always produce some turbulence. The most likely place to find turbulence is on the polar side of the stream in an upper trough. The strongest turbulence will be found in a curving jet stream associated with such a trough. If you encounter turbulence in the jet stream and you have a direct headwind or tailwind you should change course or altitude. With the wind parallel to your heading, you are likely to remain in the jet and the turbulence for a considerable distance. If you approach a jet stream from the polar side the temperature will drop. When you approach it from the tropical side, the temperature rises. Recall that there is a downdraft on the polar side and an updraft on the tropical side. Therefore, to avoid jet stream turbulence descend if the temperature is falling and climb if the temperature is rising as you approach the stream.
Fronts often have turbulence due the wind shift associated with a sharp pressure trough. Try to cross the front at right angles to minimize the time you are exposed to this turbulence.
Arctic and Tropical Weather Hazards
"Whiteout" is a visibility restricting phenomenon that occurs in the Arctic when a layer of cloudiness of uniform thickness overlies a snow or ice covered surface. Parallel rays of the sun are broken up and diffused when passing through the cloud layer so that they strike the snow surface from many angles. The diffused light then reflects back and forth between the clouds and the snow eliminating all shadows. The result is a loss of depth perception that makes takeoff or landing on snow-covered surfaces very dangerous.
"Tropical Cyclone" is the term for any low that originates over tropical oceans. Tropical cyclones are classified according to their intensity based on average one minute wind speeds. These classifications are:
Tropical Depression -- highest sustained winds up to 34 knots.
Tropical Storm -- highest sustained winds of 35 knots through 64 knots.
Hurricane or Typhoon -- highest sustained winds of 65 knots or more.
The movement of hurricanes is erratic and very difficult to predict with any degree of precision. As a general rule, hurricanes in the northern hemisphere tend to move to the northwest while they are in the lower latitudes and under the influence of the trade winds. Once they move far enough north to come under the influence of the prevailing westerlies of the mid-latitudes their track tends to curve back to the northeast.
Aviation Routine Weather Report (METAR)
An international weather reporting code (METAR) is used by all countries of the world. As of July 1, 1996, the code is used for weather reports (METAR) and forecasts (TAFs) worldwide. The reports follow the format shown in Figure 7-1-16 of the Aeronautical Information Manual.
The Weather Depiction Chart
The Weather Depiction Chart is put together from surface aviation (SA) reports to give a broad view of the weather conditions at the time of the observations. The chart shows the actual sky cover, visibility restrictions, and type of precipitation at the reporting stations. In addition, the chart groups stations that are reporting VFR, Marginal VFR or IFR weather conditions.
Stations that report a ceiling of less than 1,000 feet or a visibility of less than 3 miles are classified as IFR and included in a hatched area surrounded by a smooth line. Stations that report ceilings of 1,000 to 3,000 feet or visibilities of 3 to 5 miles are MVFR (marginal VFR) and are included in a non-hatched area surrounded by a smooth line. Stations that have a ceiling greater than 3,000 feet and visibilities greater than 5 miles are VFR and are not outlined. This chart says nothing about the weather between reporting stations.
The Terminal Aerodrome Forecast (TAF)
A Terminal Aerodrome Forecast (TAF) is a concise statement of the expected meteorological conditions at an airport during a specified period (usually 24 hours). TAFs use the same code used in the METAR weather reports (see Figure 7-1-16 of the Aeronautical Information Manual).
Enroute Forecasts
The Area Forecast (FA) is the single source reference that contains information regarding frontal movement, turbulence and icing conditions for a specific region.
A Transcribed Weather Broadcast (TWEB) route forecast provides predicted weather for a corridor 25 miles either side of a numbered cross-country route. These are broadcast over selected VORs and low frequency facilities. A pilot can also receive a TWEB from the TEL TWEB and Telephone Voice Response Systems (VRS).
A typical TWEB forecast would be "249 TWEB 252317 GFK -- MOI -- ISN, GFK VCNTY CIGS AOA 5 THSD TILL 12Z...". The translation is:
249 -- route number
TWEB -- TWEB route forecast
25 -- 25th day of the month
2317 -- valid 23Z on the 25th to 17Z on the 26th (18 hours)
GFK -- MOI -- ISN -- Route from Grand Forks (GFK) to Minot (MOI) to Williston ND (ISN)
"In the Grand Forks vicinity, ceilings at or above 5,000 feet until 1200 Z ..."
Note: Ceilings are always height above ground level.
Winds and temperatures aloft are forecast for various stations around the country. Wind directions are always relative to true north and the speed is in knots. Temperatures, in degrees Celsius, are forecast for all altitudes except for 3,000 feet. At altitudes where the wind or temperature is not forecast, a blank space is used to signify the omission. At 30,000 feet and above the minus sign is deleted from the temperature to save space.
When winds are light and variable the notation 9900 is used. When wind speeds exceed 99 knots, fifty is added to the wind direction and only the last two digits of the wind speed is printed. For example, an FD forecast of "731960" at FL390 is 230° true (73 - 50 = 23) at 119 knots with a temperature of -60°C. When winds exceed 199 knots they are coded as 199 knots. For example, winds from 280° at 205 knots are coded as 7899.
The temperature in the tropopause (36,000 feet and above) is approximately -56°C. ISA at sea level is 15°C and decreases at a rate of 2°/1,000 feet up to 36,000 feet MSL.
Forecast winds and temperatures aloft for international flights may be obtained by consulting wind and temperature aloft charts prepared by a Regional Area Forecast Center (RAFC).
Surface Analysis and Constant Pressure Charts
The Surface Analysis Chart shows pressure patterns, fronts and information on individual reporting stations. The pressure patterns are shown by lines called isobars. The isobars on a surface weather map represent lines of equal pressure reduced to sea level.
Constant pressure charts are similar in many ways to the surface analysis chart in that they show the pressure patterns and some weather conditions for reporting stations. These charts show conditions at one of five pressure levels from 850 millibars to 200 millibars. These pressure levels correspond roughly with altitudes from 5,000 feet MSL to 39,000 feet MSL. The chart is for a pressure level rather than an altitude. The altitude (in meters) of the pressure level is shown by height contours. In addition to the height contour lines, constant pressure charts can contain lines of equal temperature (isotherms) and lines of equal wind speed (isotachs). Since these are both dotted lines, be careful not to get them confused when looking at a chart. Six items of information are shown on the charts for reporting stations. These are the wind, temperature, temperature/dew point spread, height of the pressure level and the change of the height level over the previous 12 hours.
These charts can be used to locate the jet stream and its associated turbulence and wind shear. When there is a large change in wind speed over a short distance, as indicated by closely spaced isotachs, the probability of turbulence is greatly increased. Since the jet stream is associated with discontinuities in the temperature lapse rate at breaks in the tropopause, closely spaced isotherms indicate the possibility of turbulence or wind shear.
Charts can be used together to get a three dimensional view of the weather. For example, lows usually slope to the west with increasing height. If a low stops moving, it will extend almost vertically. This type of low is typical of a slow moving storm that may cause extensive and persistent cloudiness, precipitation, and generally adverse flying weather.
Prognostic Charts
A prognostic chart depicts weather conditions that are forecast to exist at a specific time in the future shown on the chart. The Low-Level Significant Prog Chart forecasts weather conditions from the surface to the 400 millibar level (about 24,000 feet). The High-Level Significant Weather Prog Chart forecasts conditions from 25,000 feet to 63,000 feet. This encompasses FL250 to FL600.
The upper two panels of the Low-Level Significant Weather Prognostic Chart are the 12-hour and the 24-hour Significant Weather Prog Charts. These two charts forecast areas of MVFR and IFR weather as well as areas of moderate or greater turbulence. In each case, the turbulence is forecast to be of moderate intensity as shown by the inverted "V" symbol. The underlined number next to the turbulence symbol indicates that the turbulence goes up to that altitude. If the turbulence started at an altitude other than the surface, a number would also appear below the line.
The lower two panels are the 12-hour and the 24-hour surface prog charts. These forecast frontal positions and areas of precipitation.
An area surrounded by a dotted and dashed line has showery precipitation. An area surrounded by a continuous line has either continuous or intermittent precipitation. If the area is shaded, the precipitation will cover more than half the area. The type of precipitation expected is shown by the symbols used within the area.
Reports and Forecasts of Hazardous Weather
The Radar Summary Chart graphically displays a collection of radar reports. It shows the types of precipitation echoes and indicates their intensity, trend, tops and bases. Shaded areas are those with significant radar returns. Areas surrounded by one line are classified as having weak to moderate echoes. Areas enclosed with two lines have strong to very strong echoes and areas inside three lines have intense to extreme echoes. The direction of an individual cell is indicated by an arrow and its speed of movement is shown by a number near the point of the arrow. Line or area movement is shown with an arrow using the "feathers" associated with wind on other charts. The wind is not shown on this chart.
A Convective Outlook (AC) describes the prospects for general thunderstorm activity during the following 24 hours. Areas in which there is a high, moderate or slight risk of severe thunderstorms are included as well as areas where thunderstorms may approach severe limits.
The Severe Weather Outlook Chart is a preliminary 24-hour outlook for thunderstorms presented in two panels. A line with an arrowhead delineates an area of probable general thunderstorm activity. An area labeled APCHG indicates probable general thunderstorm activity may approach severe intensity. "Approaching" means winds of 35 to 50 knots or hail 1/2 to 3/4 of an inch in diameter.
AIRMETs and SIGMETs are issued to alert pilots to potentially hazardous weather not adequately forecast in the current Area Forecast (FA). They are appended to the current FA and are broadcast by the FSS upon issue and at H+15 and H+45 while they are in effect. ARTCC facilities will announce that a SIGMET is in effect and the pilot can then contact the nearest FSS for the details.
AIRMET forecast:
· Moderate icing
· Moderate turbulence
· Sustained winds of 30 knots or more at the surface
· Widespread areas of ceilings less than 1,000 feet or visibilities of less than 3 miles
· Extensive mountain obscurement
SIGMET forecast:
· Severe and extreme turbulence
· Severe icing
· Widespread dust storms, sandstorms or volcanic ash lowering visibility to below three miles
Convective SIGMETs cover the following:
· Tornadoes
· Lines of thunderstorms
· Embedded thunderstorms
· Thunderstorm areas greater than or equal to intensity level 4
· Hail greater than 3/4 of an inch in diameter
Convective SIGMETs are each valid for one hour and are removed at H+40. They are reissued as necessary. On an hourly basis, an outlook is made up for each of the WST regions. This outlook covers the prospects for 2 to 6 hours.
PIREPs
A pilot weather report (PIREP) is often the most timely source of information about such weather conditions as icing and multiple cloud layers. While area forecasts and freezing level charts can give the pilot a good idea of the potential for icing, only a PIREP can let the pilot know what is happening currently. A typical PIREP appended to an SA is:
FTW UA /OV DFW 18005/TM1803/FL095/TP PA 30/SK 036 OVC 060/070 OVC 075/OVC ABV
The translation is:
FTW / UA -- PIREP from reporting station FTW.
OV DFW 18005 -- location is the DFW 180° radial at 5 miles.
TM 1803 -- time of the report is 1803.
FL095 -- altitude is 9,500 feet.
TP PA 30 -- Type of aircraft is a PA 30.
SK 036 OVC 060/070 OVC 075/OVC ABV -- Sky condition. The base of an overcast layer is at 3,600 feet with top at 6,000 feet. A second overcast layer has its base at 7,000 feet and its top is 7,500 feet. There is another overcast layer above the aircraft's altitude of 9,500 feet.
Saturday, March 22, 2008
Airline Transport Pilot Preparation : Emergencies, Hazards and Flight Physiology
Emergencies, Hazards, and Flight Physiology
Flight Emergencies and Hazards
The Pilot/Controller Glossary divides emergencies into two categories: distress and urgency. Distress is a condition of being threatened by serious and/or imminent danger and of requiring immediate assistance. Distress conditions include fire, mechanical failure or structural damage. An urgency condition is one of being concerned about safety and of requiring timely but not immediate assistance. At least an urgency condition exists the moment a pilot becomes doubtful about position, fuel endurance, weather or any other condition that could adversely affect the safety of flight. A pilot should declare an emergency when either an urgency or a distress condition exists.
When a distress or urgency condition exists, the pilot should set the radar beacon transponder to code 7700. If an aircraft is being hijacked or illegally interfered with, the pilot can alert ATC to that fact by setting the transponder to code 7500. If an aircraft has experienced a two-way communications radio failure, the pilot should set the transponder to code 7600. The pilot should also conform to the radio failure procedures of 14 CFR §91.185 (IFR operations: Two-way radio communications failure). In order to avoid false alarms, pilots should take care not to inadvertently switch through codes 7500, 7600 and 7700 when changing the transponder.
If a two-way radio failure occurs in VFR conditions, or if VFR conditions are encountered after the failure, the pilot must continue the flight under VFR and land as soon as practicable. If IFR conditions prevail, the pilot must follow the rules listed below for route, altitude and time to leave a clearance limit:
Route to be Flown
· The route assigned in the last ATC clearance received.
· If being radar vectored, fly by the direct route from the point of the radio failure to the fix, route or airway specified in the vector clearance.
· In the absence of an assigned route, fly by the route that ATC has advised may be expected in a further clearance.
· In the absence of an assigned route or expected further routing, fly by the route filed in the flight plan.
Altitude
Fly the highest of the following altitudes or flight levels for the route segment being flown:
· The altitude or flight level assigned in the last ATC clearance received.
· The minimum IFR altitude for the route segment being flown (MEA).
· The altitude or flight level that ATC has advised may be expected in a further clearance.
When to Leave a Clearance Limit
· When the clearance limit is a fix from which an approach begins, commence descent or descent and approach as close as possible to the expect further clearance (EFC) time if one has been received; or if one has not been received, as close as possible to the estimated time of arrival (ETA) as calculated from the filed or amended estimated time en route.
· If the clearance limit is not a fix from which an approach begins, leave the clearance limit at the expect further clearance (EFC) time if one has been received; or if none has been received, upon arrival over the clearance limit, and proceed to a fix from which an approach begins and commence descent or descent and approach as close as possible to the estimated time of arrival (ETA) as calculated from the filed or amended time en route.
A near mid-air collision is defined as an occurrence in which the possibility of a collision existed as the result of two aircraft coming within 500 feet or less of each other.
A minimum fuel advisory is used by a pilot to inform ATC that the fuel supply has reached a state where the pilot cannot accept any undue delay upon arrival at the destination. The minimum fuel advisory is not a declaration of an emergency, nor is it a request for priority. It does indicate that an emergency situation may develop if any undue delay occurs during the rest of the flight.
Some airports have a number of wind indicators located around the perimeter of the field as well as a center field windsock. When there is a significant difference in speed or direction between the center field windsock and one or more of the boundary wind indicators, the tower can report that a wind shear condition exists.
A safety alert will be issued to pilots being controlled by ATC in either of two circumstances. A controller will issue a safety alert when, in the controller's opinion, the aircraft's altitude will put it in unsafe proximity to the surface or an obstacle. A controller will also issue an alert if he/she becomes aware of another aircraft, not controlled by him/her, that will put both aircraft in an unsafe proximity to each other.
The wake turbulence developed by large aircraft can present a significant flight hazard to other aircraft that encounter them. The main component of wake turbulence is wing-tip vortices. These are twin vortices of air trailing behind an aircraft in flight. The vortex is a byproduct of lift. The pressure under each wing is greater than the pressure above it and this induces a flow of air outward, upward and around the wing tip. This leaves two counter-rotating spirals of air trailing behind the aircraft.
The characteristics of a vortex can be altered by changing the aircraft's configuration. The most intense vortices will be produced by an airplane that is heavy, flying slowly, and with the landing gear and flaps retracted.
The vortices generated by a large aircraft will slowly sink below its flight path and dissipate by the time they have descended about 1,000 feet. They will also tend to drift away from each other at a speed of about five knots. In a light crosswind, the upwind vortex will tend to stay over the same position on the ground while the downwind vortex will move away at about twice its normal rate. It is good wake turbulence avoidance technique to stay above and on the upwind side of the flight path of a preceding large airplane.
If the vortices reach the ground before dissipating, they will move away from each other as noted above. In a light crosswind, the upwind vortex can remain on the runway long after a large airplane has taken off or landed. The most hazardous situation is a light quartering tailwind, which not only keeps a vortex on the runway but also inhibits its dissipation.
If you plan to take off behind a large airplane, try to rotate prior to that airplane's point of rotation and climb out above and on the upwind side of the other airplane's flight path. If you plan to takeoff from a runway on which a large airplane has just landed, try to plan your lift-off point to be beyond the point where that aircraft touched down.
Flight Physiology
Even small amounts of alcohol have an adverse effect on reaction and judgment. This effect is magnified as altitude increases. No one may serve as a crewmember on a civil aircraft while:
· Within 8 hours of the consumption of any alcoholic beverage.
· While having a blood alcohol level of .04% or higher.
Runway width illusion -- A runway that is narrower than usual can create the illusion that the aircraft is higher than it really is. This can cause an unwary pilot to descend too low on approach. A wide runway creates an illusion of being too low on glide slope.
Featureless terrain illusion -- An absence of ground feature, as when landing over water, darkened areas and terrain made featureless by snow can create the illusion that the aircraft is higher than it really is.
Autokinesis -- In the dark, a static light will appear to move about when stared at for a period of time.
An effective scan pattern is necessary to ensure that a pilot will see other aircraft in time to avoid potential mid-air collisions. This means that 2/3 to 3/4 of a pilot's time should be spent scanning outside the aircraft. The best method would be to look outside for about 15 seconds and then inside for about 5 seconds. It is much easier to see an aircraft which is moving relative to the observer. Unfortunately, aircraft which present a collision hazard are usually on the horizon with little or no apparent horizontal or vertical movement. The image only grows larger as the threat aircraft gets closer. Special vigilance must be exercised for this type of situation. A pilot's most acute night vision is off-center in his/her peripheral vision. When looking for other aircraft at night, scan slowly to allow sufficient time for this off-center viewing.
All pilots who fly in instrument conditions or at night are subject to spatial disorientation. This occurs when body sensations are used to interpret flight attitudes, and there is no visual reference to the horizon. The only reliable way to overcome this disorientation is to rely entirely on the indications of the flight instruments. Some types of vertigo include:
The leans -- An abrupt correction of a banked angle can create the illusion of banking in the opposite direction.
Coriolis illusion -- An abrupt head movement during a constant rate turn can create the illusion of rotation in an entirely different axis. This illusion can be overwhelming and so rapid head movements in turns should be avoided.
Inversion illusion -- An abrupt change from a climb to straight and level flight can create the illusion of tumbling backwards.
Somatogravic illusion -- A rapid acceleration during takeoff can create the illusion of being in a nose up attitude.
Hypoxia is caused by insufficient oxygen reaching the brain. The most usual reason is the low partial pressure of oxygen encountered at altitude. Carbon monoxide poisoning is similar to hypoxia in that it causes too little oxygen to reach the brain. Carbon monoxide (usually from an exhaust leak) binds with the hemoglobin in the blood, preventing its usual oxygen-carrying function. The symptoms of both are similar and include dizziness, tingling of the hands, feet and legs, loss of higher thought processes, and unconsciousness. The sufferer may not notice or react to any of the symptoms due to his degraded mental faculties. Hyperventilation is caused by a reduction of carbon dioxide in the blood, usually due to rapid breathing in a stressful situation. The symptoms of hyperventilation are similar to hypoxia, but recovery is rapid once the rate of breathing is brought under control.
Flight Emergencies and Hazards
The Pilot/Controller Glossary divides emergencies into two categories: distress and urgency. Distress is a condition of being threatened by serious and/or imminent danger and of requiring immediate assistance. Distress conditions include fire, mechanical failure or structural damage. An urgency condition is one of being concerned about safety and of requiring timely but not immediate assistance. At least an urgency condition exists the moment a pilot becomes doubtful about position, fuel endurance, weather or any other condition that could adversely affect the safety of flight. A pilot should declare an emergency when either an urgency or a distress condition exists.
When a distress or urgency condition exists, the pilot should set the radar beacon transponder to code 7700. If an aircraft is being hijacked or illegally interfered with, the pilot can alert ATC to that fact by setting the transponder to code 7500. If an aircraft has experienced a two-way communications radio failure, the pilot should set the transponder to code 7600. The pilot should also conform to the radio failure procedures of 14 CFR §91.185 (IFR operations: Two-way radio communications failure). In order to avoid false alarms, pilots should take care not to inadvertently switch through codes 7500, 7600 and 7700 when changing the transponder.
If a two-way radio failure occurs in VFR conditions, or if VFR conditions are encountered after the failure, the pilot must continue the flight under VFR and land as soon as practicable. If IFR conditions prevail, the pilot must follow the rules listed below for route, altitude and time to leave a clearance limit:
Route to be Flown
· The route assigned in the last ATC clearance received.
· If being radar vectored, fly by the direct route from the point of the radio failure to the fix, route or airway specified in the vector clearance.
· In the absence of an assigned route, fly by the route that ATC has advised may be expected in a further clearance.
· In the absence of an assigned route or expected further routing, fly by the route filed in the flight plan.
Altitude
Fly the highest of the following altitudes or flight levels for the route segment being flown:
· The altitude or flight level assigned in the last ATC clearance received.
· The minimum IFR altitude for the route segment being flown (MEA).
· The altitude or flight level that ATC has advised may be expected in a further clearance.
When to Leave a Clearance Limit
· When the clearance limit is a fix from which an approach begins, commence descent or descent and approach as close as possible to the expect further clearance (EFC) time if one has been received; or if one has not been received, as close as possible to the estimated time of arrival (ETA) as calculated from the filed or amended estimated time en route.
· If the clearance limit is not a fix from which an approach begins, leave the clearance limit at the expect further clearance (EFC) time if one has been received; or if none has been received, upon arrival over the clearance limit, and proceed to a fix from which an approach begins and commence descent or descent and approach as close as possible to the estimated time of arrival (ETA) as calculated from the filed or amended time en route.
A near mid-air collision is defined as an occurrence in which the possibility of a collision existed as the result of two aircraft coming within 500 feet or less of each other.
A minimum fuel advisory is used by a pilot to inform ATC that the fuel supply has reached a state where the pilot cannot accept any undue delay upon arrival at the destination. The minimum fuel advisory is not a declaration of an emergency, nor is it a request for priority. It does indicate that an emergency situation may develop if any undue delay occurs during the rest of the flight.
Some airports have a number of wind indicators located around the perimeter of the field as well as a center field windsock. When there is a significant difference in speed or direction between the center field windsock and one or more of the boundary wind indicators, the tower can report that a wind shear condition exists.
A safety alert will be issued to pilots being controlled by ATC in either of two circumstances. A controller will issue a safety alert when, in the controller's opinion, the aircraft's altitude will put it in unsafe proximity to the surface or an obstacle. A controller will also issue an alert if he/she becomes aware of another aircraft, not controlled by him/her, that will put both aircraft in an unsafe proximity to each other.
The wake turbulence developed by large aircraft can present a significant flight hazard to other aircraft that encounter them. The main component of wake turbulence is wing-tip vortices. These are twin vortices of air trailing behind an aircraft in flight. The vortex is a byproduct of lift. The pressure under each wing is greater than the pressure above it and this induces a flow of air outward, upward and around the wing tip. This leaves two counter-rotating spirals of air trailing behind the aircraft.
The characteristics of a vortex can be altered by changing the aircraft's configuration. The most intense vortices will be produced by an airplane that is heavy, flying slowly, and with the landing gear and flaps retracted.
The vortices generated by a large aircraft will slowly sink below its flight path and dissipate by the time they have descended about 1,000 feet. They will also tend to drift away from each other at a speed of about five knots. In a light crosswind, the upwind vortex will tend to stay over the same position on the ground while the downwind vortex will move away at about twice its normal rate. It is good wake turbulence avoidance technique to stay above and on the upwind side of the flight path of a preceding large airplane.
If the vortices reach the ground before dissipating, they will move away from each other as noted above. In a light crosswind, the upwind vortex can remain on the runway long after a large airplane has taken off or landed. The most hazardous situation is a light quartering tailwind, which not only keeps a vortex on the runway but also inhibits its dissipation.
If you plan to take off behind a large airplane, try to rotate prior to that airplane's point of rotation and climb out above and on the upwind side of the other airplane's flight path. If you plan to takeoff from a runway on which a large airplane has just landed, try to plan your lift-off point to be beyond the point where that aircraft touched down.
Flight Physiology
Even small amounts of alcohol have an adverse effect on reaction and judgment. This effect is magnified as altitude increases. No one may serve as a crewmember on a civil aircraft while:
· Within 8 hours of the consumption of any alcoholic beverage.
· While having a blood alcohol level of .04% or higher.
Runway width illusion -- A runway that is narrower than usual can create the illusion that the aircraft is higher than it really is. This can cause an unwary pilot to descend too low on approach. A wide runway creates an illusion of being too low on glide slope.
Featureless terrain illusion -- An absence of ground feature, as when landing over water, darkened areas and terrain made featureless by snow can create the illusion that the aircraft is higher than it really is.
Autokinesis -- In the dark, a static light will appear to move about when stared at for a period of time.
An effective scan pattern is necessary to ensure that a pilot will see other aircraft in time to avoid potential mid-air collisions. This means that 2/3 to 3/4 of a pilot's time should be spent scanning outside the aircraft. The best method would be to look outside for about 15 seconds and then inside for about 5 seconds. It is much easier to see an aircraft which is moving relative to the observer. Unfortunately, aircraft which present a collision hazard are usually on the horizon with little or no apparent horizontal or vertical movement. The image only grows larger as the threat aircraft gets closer. Special vigilance must be exercised for this type of situation. A pilot's most acute night vision is off-center in his/her peripheral vision. When looking for other aircraft at night, scan slowly to allow sufficient time for this off-center viewing.
All pilots who fly in instrument conditions or at night are subject to spatial disorientation. This occurs when body sensations are used to interpret flight attitudes, and there is no visual reference to the horizon. The only reliable way to overcome this disorientation is to rely entirely on the indications of the flight instruments. Some types of vertigo include:
The leans -- An abrupt correction of a banked angle can create the illusion of banking in the opposite direction.
Coriolis illusion -- An abrupt head movement during a constant rate turn can create the illusion of rotation in an entirely different axis. This illusion can be overwhelming and so rapid head movements in turns should be avoided.
Inversion illusion -- An abrupt change from a climb to straight and level flight can create the illusion of tumbling backwards.
Somatogravic illusion -- A rapid acceleration during takeoff can create the illusion of being in a nose up attitude.
Hypoxia is caused by insufficient oxygen reaching the brain. The most usual reason is the low partial pressure of oxygen encountered at altitude. Carbon monoxide poisoning is similar to hypoxia in that it causes too little oxygen to reach the brain. Carbon monoxide (usually from an exhaust leak) binds with the hemoglobin in the blood, preventing its usual oxygen-carrying function. The symptoms of both are similar and include dizziness, tingling of the hands, feet and legs, loss of higher thought processes, and unconsciousness. The sufferer may not notice or react to any of the symptoms due to his degraded mental faculties. Hyperventilation is caused by a reduction of carbon dioxide in the blood, usually due to rapid breathing in a stressful situation. The symptoms of hyperventilation are similar to hypoxia, but recovery is rapid once the rate of breathing is brought under control.
Airline Transport Pilot Preparation : Flight Operations
Flight Operations
Airspace
A turbine-powered airplane or a large airplane must enter Class D airspace at an altitude of at least 1,500 feet AGL and maintain that altitude in the traffic pattern until a lower altitude is necessary for a safe landing. When taking off, the pilot of a turbine-powered airplane or a large airplane must climb as rapidly as practicable to an altitude of 1,500 feet AGL.
No person may operate an aircraft within Class B airspace unless a proper authorization from ATC has been received prior to entry. An IFR clearance is not necessarily required. Unless otherwise authorized by ATC, every person flying a large turbine-engine-powered airplane to or from the primary airport in Class B airspace must operate at or above the floor of Class B airspace.
All Class C airspace has the same dimensions with minor site variations. They are composed of two circles both centered on the primary airport. The surface area has a radius of 5 nautical miles and extends from the surface up to 4,000 feet above the airport. The shelf area has a radius of 10 nautical miles and extends vertically from 1,200 feet AGL up to 4,000 feet above the primary airport. In addition to the Class C airspace proper, there is an outer area with a radius of 20 nautical miles and vertical coverage from the lower limits of the radio/radar coverage up to the top of the approach control facility's delegated airspace.
The only equipment requirements for an aircraft to operate within Class C airspace are a two-way radio and a transponder. No specific pilot certification is required.
The following services are provided within Class C airspace:
· Sequencing of all arriving aircraft to the primary airport.
· Standard IFR separation between IFR aircraft.
· Between IFR and VFR aircraft -- traffic advisories and conflict resolution so that radar targets do not touch, or 500 feet vertical separation.
· Between VFR aircraft, traffic advisories and as appropriate, safety alerts.
The same services are provided in the outer area when two-way radio and radar contact is established. There is no requirement for VFR participation in the outer area.
No one may operate an aircraft below 10,000 feet MSL at an indicated speed greater than 250 knots. No one may operate an aircraft within Class D airspace at an indicated airspeed of more than 200 knots. There is no special speed limit for operations within Class B airspace other than the 250-knot limit when below 10,000 feet MSL. When operating beneath the lateral limits of Class B airspace, the indicated airspeed cannot exceed 200 knots. If the minimum safe airspeed for any particular operation is greater than the maximum speed prescribed by 14 CFR §91.117, the aircraft may be operated at that minimum speed.
Warning Areas are so designated because they are located in international (and therefore uncontrolled) airspace and have invisible hazards to flight. The purpose of a Military Operating Area (MOA) is to separate IFR traffic from military training activities. Normally, ATC will not clear an IFR flight into an MOA if it is in use by the military. In an MOA, the individual pilots are responsible for collision avoidance. VR Military Training Routes which extend above 1,500 feet AGL, and IR Training Routes are depicted on IFR Enroute Low Altitude Charts.
When a flight is to penetrate an Air Defense Identification Zone (ADIZ), it must be on either an IFR or a DVFR flight plan. The flight must penetrate the ADIZ within +/-5 minutes of the flight plan estimate and within 10 miles when over land or within 20 miles when over water. These were formerly referred to as domestic and coastal ADIZs in the AIM.
A VFR-On-Top clearance is an IFR authorization to fly the cleared route at the VFR altitude of the pilot's choice. To request VFR-On-Top, the flight must be able to maintain the minimum VFR visibility and cloud clearances appropriate for the airspace and altitude. This may be done above, below or between the clouds, if any. While the pilot is expected to comply with all IFR rules, ATC will provide traffic advisories only. VFR-On-Top will not be authorized in Class A airspace. VFR weather minimums must be observed when operating under a VFR-On-Top clearance.
An air carrier flight may conduct day Over-the-Top operations below the minimum IFR altitude if the following are observed:
· The flight must be at least 1,000 feet above the top of a broken or overcast layer.
· The top of the clouds are generally uniform and level.
· The flight visibility is at least five miles.
· The base of any higher ceiling is at least 1,000 feet above the minimum IFR altitude.
OROCA is an off-route altitude which provides obstruction clearance with a 1,000-foot buffer in nonmountainous terrain area, and a 2,000-foot buffer in designated mountainous areas within the U.S. Minimum Vectoring Altitudes (MVAs) are established for use by ATC when radar is exercised; MVA charts are prepared by air traffic facilities at locations where there are many different minimum IFR altitudes. Minimum Safe/Sector Altitudes (MSAs) are published for emergency use on IAP charts; they are expressed in MSL and normally have a 25 NM radius. However, this radius may be expanded to 30 NM if necessary to encompass the airport landing surfaces.
NOTAMs (NOtices To AirMen)
NOTAMs are time-critical information notices which are either temporary in nature or not known about far enough in advance to permit publication in charts and other such data. NOTAM information includes such things as airport or primary runway closures, changes in the status of navigational aids, ILS's, radar service availability and other information essential to planned en route, terminal or landing operations. There are three types of NOTAMs:
· The FDC NOTAM covers things such as amendments to published instrument approach procedures and aeronautical charts, and are considered to be regulatory in nature.
· NOTAM (D)s are disseminated for all navigational facilities that are part of the national airspace system. The information is available nationwide and is appended to the hourly weather reports.
· A NOTAM (L) includes such information as taxiway closures, personnel and equipment near or crossing runways, airport rotating beacon outages and airport lighting aids that do not affect instrument approaches. NOTAM (L)s receive only local area distribution.
Items on the Flight Plan
An IFR flight plan should be filed at least 30 minutes prior to the departure time, and pilots should request their IFR clearance no more than 10 minutes prior to taxi.
In a composite flight plan, one portion of the flight is IFR and the other is VFR. Both the VFR and IFR boxes of the flight plan form should be checked and the route defined in the route of flight box as with any other flight plan. The flight plan should also note where the switch from one type of clearance to the other is planned. If the first part of the flight is IFR, the pilot should cancel with ATC and open the VFR portion with the nearest Flight Service Station by radio. If the first portion is VFR, the pilot should close the VFR portion with the nearest Flight Service Station and request the IFR clearance at least five minutes prior to the IFR portion of the flight.
If the flight is to be flown on established airways, the route should be defined using the airways or jet routes with transitions. Intermediate VORs and fixes on an airway need not be listed. If filing for an off-airway direct route, list all the radio fixes over which the flight will pass. Pilots of appropriately equipped aircraft may file for random RNAV routes. The following rules must be observed:
· Radar monitoring by ATC must be available along the entire proposed route.
· Plan the random route portion to begin and end over appropriate departure and arrival transition fixes or navigation aids appropriate for the altitude structure used for the flight. Use of DPs and STARs, where available, is recommended.
· Define the random route by waypoints. Use degree-distance fixes based on navigational aids appropriate for the altitude structure used. Above FL390 latitude/longitude fixes may be used to define the route.
· List at least one waypoint for each Air Route Traffic Control Center through which the flight will pass. The waypoint must be within 200 NM of the preceding Center's boundary.
A pilot may file a flight plan to an airport containing a special or privately-owned instrument approach procedure only upon approval of the owner.
Air ambulance flights and air carrier flights responding to medical emergencies will receive expedited handling by ATC when necessary. When appropriate, the word "Lifeguard" should be entered in the remarks section of the flight plan. It should also be used in the flight's radio call sign as in, "Lifeguard Delta Thirty-Seven."
Alternate Airport Planning
Alternate Airport for Destination -- Domestic Air Carriers: Unless the weather at the destination meets certain criteria, an alternate must be listed in the dispatch release (and flight plan) for each destination airport. If the weather at the first listed alternate is marginal (as defined by the operations specifications) at least one additional alternate must be listed.
Alternate Airport for Destination -- Flag Carriers: An alternate airport must be listed in the dispatch release (and flight plan) for all flag air carrier flights longer than 6 hours. An alternate is not required for a flag air carrier flight if it is scheduled for less than 6 hours and the weather forecast for the destination meets certain criteria. For the period from 1 hour before to 1 hour after the estimated time of arrival:
· The ceiling must be forecast to be at least 1,500 feet above the lowest minimums or 2,000 feet, whichever is higher; and
· The visibility must be forecast to be 3 miles, or 2 miles greater than the lowest applicable visibility minimum, whichever is greater.
Alternate Airport for Destination -- Supplemental Air Carriers and Commercial Operators: Except for certain operations, a supplemental air carrier or commercial operator must always list an alternate airport regardless of existing or forecast weather conditions.
An airport cannot be listed as an alternate in the dispatch or flight release unless the appropriate weather reports and forecasts indicate that the weather conditions will be at or above the alternate weather minimums specified in the certificate holder's operations specifications for that airport, when the flight arrives. Alternate weather minimums are for planning purposes only and do not apply to actual operations. If an air carrier flight actually diverts to an alternate airport, the crew may use the actual weather minimums shown on the IAP (Instrument Approach Procedure) Chart for that airport.
If the weather conditions at the departure airport are below landing minimums in the airline's operations specifications, a departure alternate must be listed in the dispatch or the flight release. Weather at alternate airports must meet the conditions for alternates in the operations specifications. The maximum distance to the departure alternate for a two-engine airplane cannot be more than 1 hour from the departure airport in still air with one engine operating. The distance to the departure alternate for an airplane with three or more engines cannot be more than 2 hours from the departure airport in still air with one engine inoperative.
ATC Clearances
No one may operate an aircraft in Class A, B, C, D or E airspace under Instrument Flight Rules (IFR) unless he/she has filed an IFR flight plan and received an appropriate ATC clearance. No flight plan or clearance is required for IFR operations in Class G airspace.
IFR clearances always contain:
· A clearance limit (usually the destination);
· Route of flight;
· Altitude assignment; and
· Departure instructions (could be a DP).
The words "cleared as filed" replace only the route of flight portion of a normal clearance. The controller will still state the destination airport, the enroute altitude (or initial altitude and expected final altitude) and DP if appropriate. If a STAR is filed on the flight plan, it is considered part of the enroute portion of the flight plan and is included in the term "cleared as filed."
When an ATC clearance has been received, you may not deviate from it (except in an emergency) unless an amended clearance is received. If you are uncertain of the meaning of an ATC clearance or the clearance appears to be contrary to a regulation, you should immediately request a clarification. When you receive a clearance you should always read back altitude assignments, altitude restrictions, and vectors. A Departure Procedure (DP) may contain these elements but they need not be included in the readback unless the ATC controller specifically states them.
At airports with pretaxi clearance delivery, a pilot should call for the clearance 10 minutes prior to the desired taxi time. After receiving clearance on the clearance delivery frequency, the pilot should call ground control for taxi when ready.
Occasionally, an aircraft with an IFR release will be held on the ground for traffic management reasons. The traffic may be too heavy or weather may be causing ATC delays. If this happens to an aircraft waiting for takeoff, it will be given a hold for release instruction.
When ATC can anticipate long delays for IFR aircraft, they will establish gate hold procedures. The idea is to hold aircraft at the gate rather than cause congestion and unnecessary fuel burn on the taxiways while waiting for an IFR release. Ground control will instruct aircraft when to start engines. ATC expects that turbine-powered aircraft will be ready for takeoff as soon as they reach the runway after having been released from gate hold.
When departing uncontrolled airports, IFR flights will often receive a void time with their clearance. The void time is a usually a 30-minute window of time during which the aircraft must takeoff for its IFR clearance to be valid. If unable to comply with the void time, a pilot must receive another clearance with an amended void time.
The flight plan of an airborne IFR aircraft may only be canceled when the aircraft is in VFR weather conditions and outside of Class A airspace.
Takeoff Procedures
Unless otherwise authorized by the FAA, an air carrier flight may not takeoff unless the weather meets the prescribed takeoff minimums for that airport. If takeoff minimums are not published for the airport, the following visibility is required for takeoff:
· For aircraft having two engines or less: 1 statute mile visibility.
· For aircraft having three or more engines: 1/2 statute mile visibility.
If an air carrier flight is going to takeoff from an airport that is not listed in its operations specifications, the pilot must observe the takeoff weather minimums published for that airport. If no takeoff weather minimums are published for that airport, then the pilot must be sure that the ceiling and visibility meet a sliding scale requirement of 800-2 or 900-1-1/2 or 1,000 -1.
Instrument Approaches
This section is limited to rules and procedures common to most, or all approaches, or procedures that may be used in connection with published instrument approaches.
Contact and visual approaches are both IFR authorizations to proceed to an airport visually. A visual approach may be authorized by ATC to reduce pilot or controller workload and to expedite traffic by shortening flight paths to the airport. The weather must be VFR and the pilot must report either the airport or the preceding aircraft in sight. Either the pilot or ATC may initiate a visual approach. A contact approach may be initiated only by the pilot. The weather need not be VFR but the aircraft must be clear of the clouds, have at least 1 mile visibility and be able to proceed to the landing airport visually.
When an airport has ILS or MLS approaches to parallel runways at least 4,300 feet apart, ATC may conduct approaches to both runways simultaneously. The pilots will be informed if simultaneous approaches are in progress. To ensure safe separation between aircraft, radar monitoring is provided on the tower frequency. A pilot must report any malfunctioning aircraft receivers if he/she has been informed that simultaneous approaches are in progress.
Occasionally, a pilot will be asked to fly an instrument approach to a runway and then fly a visual "sidestep" maneuver to land on a parallel runway. This sidestep maneuver should be executed as soon as possible after the runway environment is in sight.
If a pilot is being radar vectored when an approach clearance is received, he/she must maintain the last assigned altitude until the aircraft is established on a segment of a published route or approach procedure unless a different altitude is assigned by ATC. If a flight is being radar vectored to the final approach course and intercepts a published portion of the course, the pilot may not descend to the published altitudes until cleared for the approach. If a flight has not been cleared for approach while on a radar vector and it becomes apparent that the current vector will take it across the final approach course, the pilot should advise ATC of the situation. Do not turn to intercept the approach course unless cleared to do so.
Unless ATC issues a clearance otherwise, no pilot may make a procedure turn on an instrument approach if any of the following apply:
· The flight is radar vectored to the final approach course or fix
· The flight makes a timed approach from a holding fix
· The approach procedure specifies "No PT"
When the approach procedure involves a procedure turn, a maximum speed of not greater than 200 KIAS should be observed from first overheading the course reversal IAF through the procedure turn maneuver, to ensure containment with the obstruction clearance area.
Except for Category II and III approaches, if RVR minimums for takeoff or landing are prescribed in an instrument approach procedure, but the RVR is not reported for the runway intended, the ground visibilities may be substituted. These may be found in FAA Legend 7.
A pilot may not continue an approach past the final approach fix or on to the final approach segment unless the latest weather report for the airport indicates that the visibility is equal to, or greater than, the visibility required for the approach procedure. If a pilot has begun the final approach segment and then receives a report of below minimum conditions, he/she may continue the approach to the DH or MDA.
To descend below the published DH or MDA on an instrument approach, one of the following must be distinctly visible and identifiable to the pilot:
· Approach light system, except that the pilot may not descend below 100 feet above the touchdown zone elevation using the approach lights as a reference unless the red terminating bars or red side row bars are also distinctly visible and identifiable.
· Threshold
· Threshold markings
· Threshold lights
· Runway end identifier lights
· Visual approach slope indicator
· Touchdown zone or touchdown zone markings
· Touchdown zone lights
· Runway or runway markings
· Runway lights
A pilot must initiate a missed approach from an ILS upon arrival at the DH on the glide slope if none of the required visual references is distinctly visible. If visual contact is lost anytime after descending below the DH but before touchdown, the pilot must start a missed approach.
If a pilot loses visual reference while circling to land from an instrument approach, he/she should follow the missed approach procedure published for the approach used. The pilot should make an initial climbing turn toward the landing runway to establish the aircraft on the missed approach course.
An Airport Surveillance Radar (ASR) approach is one in which an ATC radar controller provides directional guidance and distance to the runway information to the pilot. The only airborne equipment required is an operating radio receiver. The controller will tell the pilot when the aircraft is at the missed approach point and give missed approach instructions as required. If the pilot desires to execute a missed approach prior to the missed approach point, he/she should inform the controller, who will then issue missed approach instructions.
Landing
Except for emergencies, the landing priority of aircraft arriving at a tower controlled airport is on "first-come, first-served" basis. When landing at a tower controlled airport, an aircraft should exit the runway at the first suitable taxiway and remain on the tower frequency until instructed to do otherwise. The aircraft should not turn onto any other taxiway unless a clearance to do so has been received.
If a flight is making an IFR approach at an uncontrolled airport, radar service will be terminated when the aircraft lands or when the controller tells the pilot to change to advisory frequency. After changing to the advisory frequency, the pilot should broadcast his/her intentions and continually update position reports. The advisory frequency will be an FSS frequency, or if there is no FSS on the field, a UNICOM frequency.
ATC furnishes pilots' braking action reports using the terms "good," "fair," "poor" and "nil." If you give a braking action report to ATC, you should use the same terminology.
Communications
The "Sterile Cockpit" Rule: Regulations say only those duties required for the safe operation of the aircraft are allowed during critical phases of flight. Critical phases of flight are defined as climb and descent when below 10,000 feet, taxi, takeoff, and landing. Excluded from the definition of critical phase of flight are any operations at or above 10,000 feet and cruise flight below 10,000 feet. Activities which are prohibited during critical phases of flight include filling out logs, ordering galley supplies, making passenger announcements or pointing out sights of interest. Activities such as eating meals or engaging in nonessential conversations are also prohibited.
The following should be reported without ATC request.
· Vacating a previously assigned altitude for a newly assigned one.
· An altitude change when operating under a VFR-On-Top clearance.
· When unable to climb or descend at a rate of at least 500 feet per minute.
· When an approach has been missed.
· A change in cruising true airspeed of 10 knots or 5%, whichever is greater.
· The time and altitude (or Flight Level) upon reaching a holding fix or clearance limit.
· When leaving an assigned holding fix or point.
· The malfunction of navigation, approach or communication equipment.
· Any information pertaining to the safety of flight.
In addition to the reports listed above, when not in radar contact a pilot must report:
· When over designated compulsory reporting points.
· When leaving the final approach fix inbound on an instrument approach.
· When it becomes apparent that an estimate of arrival time over a fix is in error by more than 3 minutes.
Occasionally an ATC controller will query a pilot about the aircraft's altitude or course. For example, a controller says "Verify 9000," meaning he/she wants confirmation that the aircraft is at 9,000 feet altitude. If the aircraft is not at that altitude, the pilot should reply, "Negative, maintaining 8,000 as assigned." No climb or descent should be started unless specifically assigned by the controller.
Pilots should notify controllers on initial contact that they have received the ATIS broadcast by repeating the alphabetical code word appended to the broadcast. For example, "Information Sierra received."
Speed Adjustments
ATC controllers often issue speed adjustments to radar controlled aircraft to achieve or maintain the desired separation. The following minimum speeds are usually observed:
· Turbine-powered aircraft below 10,000 feet: 210 knots.
· Turbine-powered aircraft departing an airport: 230 knots.
If an ATC controller assigns a speed which is too fast or too slow for the operating limitations of the aircraft under the existing circumstances, the pilot should advise ATC of the speed that will be used. The controller will then issue instructions based on that speed.
Because of the great differences in speed and operating characteristics of helicopters and airplanes, they are usually assigned different routing. Occasionally, larger/faster helicopters are integrated with fixed-wing aircraft. These situations could occur on IFR flights, routes that avoid noise-sensitive areas, or when the helicopter is assigned runways or taxiways to avoid downwash in congested areas.
Holding
Holding may be necessary when ATC is unable to clear a flight to its destination. VORs, non-directional beacons, airway intersections, and DME fixes may all be used as holding points. Flying a holding pattern involves two turns and two straight-and-level legs.
At and below 14,000 feet MSL (no wind), the aircraft flies the specified course inbound to the fix, turns to the right 180°, flies a parallel course outbound for 1 minute, again turns 180° to the right, and flies 1 minute inbound to the fix. Above 14,000 feet MSL, the inbound leg length is 1-1/2 minutes. If a nonstandard pattern is to be flown, ATC will specify left turns.
When 3 minutes or less from the holding fix, the pilot is expected to start a speed reduction so as to cross the fix at or below the maximum holding airspeed. For all aircraft between MHA (minimum holding altitude) and 6,000 feet MSL, holding speed is 200 KIAS. For all aircraft between 6,001 and 14,000 feet MSL, holding speed is 230 KIAS. For all aircraft 14,000 feet MSL and above, holding speed is 265 KIAS. Exceptions to these speeds will be indicated by an icon.
The aircraft is in a holding pattern as of the initial time of arrival over the fix, and that time should be reported to ATC. The initial outbound leg is flown for 1 minute at or below 14,000 feet MSL. Subsequently, timing of the outbound leg should be adjusted as necessary to arrive at the proper inbound leg length. Timing of the outbound leg begins over or abeam the fix, whichever occurs later. If the abeam position cannot be determined, start timing when the turn to outbound is completed. The same entry and holding procedures apply to DME holding, except distance in nautical miles are used to establish leg length.
The FAA has three recommended methods for entering a holding pattern. An aircraft approaching from within sector (A) would fly a parallel entry by turning left to parallel the outbound course, making another left turn to remain in protected airspace, and returning to the holding fix. Aircraft approaching from sector (B) would fly a teardrop entry, by flying outbound on a track of 30° or less to the holding course, and then making a right turn to intercept the holding course inbound to the fix. Those approaching from within sector (C) would fly a direct entry by turning right to fly the pattern.
If the holding pattern is charted, the controller may omit all holding instructions, except the holding direction and the statement "as published." Pilots are expected to hold in the pattern depicted even if it means crossing the clearance limit. If the holding pattern to be used is not depicted on charts, ATC will issue general holding instructions. The holding clearance will include the following information: direction of holding from the fix in terms of the eight cardinal compass points; holding fix; radial, course, bearing, airway, or route on which the aircraft is to hold; leg length in miles if DME or RNAV is to be used; direction of turn if left turns are to be made; time to expect further clearance and any pertinent additional delay information.
Charts
The pilot-in-command must ensure that the appropriate aeronautical charts are on board the aircraft for each flight.
There are a number of questions that require reference to a segment of the Airport/Facility Directory. The legend for this publication is available in the FAA Legends 13 through 19.
Most of the questions concerning interpretation of Approach Charts, DPs and STARs can be answered by referring to the appropriate legend. These legends are available during the test in FAA Legend 40.
There are a few questions that require you to interpret the symbology on Enroute Charts. Unlike the other charts, no legend is available in the test book.
Departure Procedures (DPs) are depicted in one of two basic forms. Pilot Navigation (Pilot NAV) DPs are established where the pilot is primarily responsible for navigation on the DP route. Vector DPs are established where ATC will provide radar navigational guidance to an assigned route or fix. A vector DP will often include procedures to be followed in the event of a two-way communication radio failure.
Standard Terminal Arrival Routes (STARs) are ATC-coded IFR arrival routes established for certain airports. STARs purpose is to simplify clearance delivery procedures. ATC will assign a STAR to a civil aircraft whenever they deem it appropriate.
A few RNAV approaches based on LORAN-C have been established around the country. This approach is flown just like any other nonprecision instrument approach procedure.
The Jet Route system consists of jet routes established from 18,000 feet MSL to FL450 inclusive.
The GPS Approach Overlay Program permits pilots to use GPS avionics under IFR for flying existing instrument approach procedures, except localizer (LOC), localizer directional aid (LDA), and simplified directional facility (SDF) procedures. Aircraft navigating by GPS are considered to be RNAV aircraft. Therefore, the appropriate equipment suffix must be included in the ATC flight plan. The word "or" in the approach title indicates that approach is in Phase III of the GPS Overlay Program. This allows the approach to be flown without reference of any kind to the ground-based NAVAIDs associated with the approach. When using GPS for the approach at the destination airport, the alternate must be an approach other than a GPS or LORAN-C.
Airspace
A turbine-powered airplane or a large airplane must enter Class D airspace at an altitude of at least 1,500 feet AGL and maintain that altitude in the traffic pattern until a lower altitude is necessary for a safe landing. When taking off, the pilot of a turbine-powered airplane or a large airplane must climb as rapidly as practicable to an altitude of 1,500 feet AGL.
No person may operate an aircraft within Class B airspace unless a proper authorization from ATC has been received prior to entry. An IFR clearance is not necessarily required. Unless otherwise authorized by ATC, every person flying a large turbine-engine-powered airplane to or from the primary airport in Class B airspace must operate at or above the floor of Class B airspace.
All Class C airspace has the same dimensions with minor site variations. They are composed of two circles both centered on the primary airport. The surface area has a radius of 5 nautical miles and extends from the surface up to 4,000 feet above the airport. The shelf area has a radius of 10 nautical miles and extends vertically from 1,200 feet AGL up to 4,000 feet above the primary airport. In addition to the Class C airspace proper, there is an outer area with a radius of 20 nautical miles and vertical coverage from the lower limits of the radio/radar coverage up to the top of the approach control facility's delegated airspace.
The only equipment requirements for an aircraft to operate within Class C airspace are a two-way radio and a transponder. No specific pilot certification is required.
The following services are provided within Class C airspace:
· Sequencing of all arriving aircraft to the primary airport.
· Standard IFR separation between IFR aircraft.
· Between IFR and VFR aircraft -- traffic advisories and conflict resolution so that radar targets do not touch, or 500 feet vertical separation.
· Between VFR aircraft, traffic advisories and as appropriate, safety alerts.
The same services are provided in the outer area when two-way radio and radar contact is established. There is no requirement for VFR participation in the outer area.
No one may operate an aircraft below 10,000 feet MSL at an indicated speed greater than 250 knots. No one may operate an aircraft within Class D airspace at an indicated airspeed of more than 200 knots. There is no special speed limit for operations within Class B airspace other than the 250-knot limit when below 10,000 feet MSL. When operating beneath the lateral limits of Class B airspace, the indicated airspeed cannot exceed 200 knots. If the minimum safe airspeed for any particular operation is greater than the maximum speed prescribed by 14 CFR §91.117, the aircraft may be operated at that minimum speed.
Warning Areas are so designated because they are located in international (and therefore uncontrolled) airspace and have invisible hazards to flight. The purpose of a Military Operating Area (MOA) is to separate IFR traffic from military training activities. Normally, ATC will not clear an IFR flight into an MOA if it is in use by the military. In an MOA, the individual pilots are responsible for collision avoidance. VR Military Training Routes which extend above 1,500 feet AGL, and IR Training Routes are depicted on IFR Enroute Low Altitude Charts.
When a flight is to penetrate an Air Defense Identification Zone (ADIZ), it must be on either an IFR or a DVFR flight plan. The flight must penetrate the ADIZ within +/-5 minutes of the flight plan estimate and within 10 miles when over land or within 20 miles when over water. These were formerly referred to as domestic and coastal ADIZs in the AIM.
A VFR-On-Top clearance is an IFR authorization to fly the cleared route at the VFR altitude of the pilot's choice. To request VFR-On-Top, the flight must be able to maintain the minimum VFR visibility and cloud clearances appropriate for the airspace and altitude. This may be done above, below or between the clouds, if any. While the pilot is expected to comply with all IFR rules, ATC will provide traffic advisories only. VFR-On-Top will not be authorized in Class A airspace. VFR weather minimums must be observed when operating under a VFR-On-Top clearance.
An air carrier flight may conduct day Over-the-Top operations below the minimum IFR altitude if the following are observed:
· The flight must be at least 1,000 feet above the top of a broken or overcast layer.
· The top of the clouds are generally uniform and level.
· The flight visibility is at least five miles.
· The base of any higher ceiling is at least 1,000 feet above the minimum IFR altitude.
OROCA is an off-route altitude which provides obstruction clearance with a 1,000-foot buffer in nonmountainous terrain area, and a 2,000-foot buffer in designated mountainous areas within the U.S. Minimum Vectoring Altitudes (MVAs) are established for use by ATC when radar is exercised; MVA charts are prepared by air traffic facilities at locations where there are many different minimum IFR altitudes. Minimum Safe/Sector Altitudes (MSAs) are published for emergency use on IAP charts; they are expressed in MSL and normally have a 25 NM radius. However, this radius may be expanded to 30 NM if necessary to encompass the airport landing surfaces.
NOTAMs (NOtices To AirMen)
NOTAMs are time-critical information notices which are either temporary in nature or not known about far enough in advance to permit publication in charts and other such data. NOTAM information includes such things as airport or primary runway closures, changes in the status of navigational aids, ILS's, radar service availability and other information essential to planned en route, terminal or landing operations. There are three types of NOTAMs:
· The FDC NOTAM covers things such as amendments to published instrument approach procedures and aeronautical charts, and are considered to be regulatory in nature.
· NOTAM (D)s are disseminated for all navigational facilities that are part of the national airspace system. The information is available nationwide and is appended to the hourly weather reports.
· A NOTAM (L) includes such information as taxiway closures, personnel and equipment near or crossing runways, airport rotating beacon outages and airport lighting aids that do not affect instrument approaches. NOTAM (L)s receive only local area distribution.
Items on the Flight Plan
An IFR flight plan should be filed at least 30 minutes prior to the departure time, and pilots should request their IFR clearance no more than 10 minutes prior to taxi.
In a composite flight plan, one portion of the flight is IFR and the other is VFR. Both the VFR and IFR boxes of the flight plan form should be checked and the route defined in the route of flight box as with any other flight plan. The flight plan should also note where the switch from one type of clearance to the other is planned. If the first part of the flight is IFR, the pilot should cancel with ATC and open the VFR portion with the nearest Flight Service Station by radio. If the first portion is VFR, the pilot should close the VFR portion with the nearest Flight Service Station and request the IFR clearance at least five minutes prior to the IFR portion of the flight.
If the flight is to be flown on established airways, the route should be defined using the airways or jet routes with transitions. Intermediate VORs and fixes on an airway need not be listed. If filing for an off-airway direct route, list all the radio fixes over which the flight will pass. Pilots of appropriately equipped aircraft may file for random RNAV routes. The following rules must be observed:
· Radar monitoring by ATC must be available along the entire proposed route.
· Plan the random route portion to begin and end over appropriate departure and arrival transition fixes or navigation aids appropriate for the altitude structure used for the flight. Use of DPs and STARs, where available, is recommended.
· Define the random route by waypoints. Use degree-distance fixes based on navigational aids appropriate for the altitude structure used. Above FL390 latitude/longitude fixes may be used to define the route.
· List at least one waypoint for each Air Route Traffic Control Center through which the flight will pass. The waypoint must be within 200 NM of the preceding Center's boundary.
A pilot may file a flight plan to an airport containing a special or privately-owned instrument approach procedure only upon approval of the owner.
Air ambulance flights and air carrier flights responding to medical emergencies will receive expedited handling by ATC when necessary. When appropriate, the word "Lifeguard" should be entered in the remarks section of the flight plan. It should also be used in the flight's radio call sign as in, "Lifeguard Delta Thirty-Seven."
Alternate Airport Planning
Alternate Airport for Destination -- Domestic Air Carriers: Unless the weather at the destination meets certain criteria, an alternate must be listed in the dispatch release (and flight plan) for each destination airport. If the weather at the first listed alternate is marginal (as defined by the operations specifications) at least one additional alternate must be listed.
Alternate Airport for Destination -- Flag Carriers: An alternate airport must be listed in the dispatch release (and flight plan) for all flag air carrier flights longer than 6 hours. An alternate is not required for a flag air carrier flight if it is scheduled for less than 6 hours and the weather forecast for the destination meets certain criteria. For the period from 1 hour before to 1 hour after the estimated time of arrival:
· The ceiling must be forecast to be at least 1,500 feet above the lowest minimums or 2,000 feet, whichever is higher; and
· The visibility must be forecast to be 3 miles, or 2 miles greater than the lowest applicable visibility minimum, whichever is greater.
Alternate Airport for Destination -- Supplemental Air Carriers and Commercial Operators: Except for certain operations, a supplemental air carrier or commercial operator must always list an alternate airport regardless of existing or forecast weather conditions.
An airport cannot be listed as an alternate in the dispatch or flight release unless the appropriate weather reports and forecasts indicate that the weather conditions will be at or above the alternate weather minimums specified in the certificate holder's operations specifications for that airport, when the flight arrives. Alternate weather minimums are for planning purposes only and do not apply to actual operations. If an air carrier flight actually diverts to an alternate airport, the crew may use the actual weather minimums shown on the IAP (Instrument Approach Procedure) Chart for that airport.
If the weather conditions at the departure airport are below landing minimums in the airline's operations specifications, a departure alternate must be listed in the dispatch or the flight release. Weather at alternate airports must meet the conditions for alternates in the operations specifications. The maximum distance to the departure alternate for a two-engine airplane cannot be more than 1 hour from the departure airport in still air with one engine operating. The distance to the departure alternate for an airplane with three or more engines cannot be more than 2 hours from the departure airport in still air with one engine inoperative.
ATC Clearances
No one may operate an aircraft in Class A, B, C, D or E airspace under Instrument Flight Rules (IFR) unless he/she has filed an IFR flight plan and received an appropriate ATC clearance. No flight plan or clearance is required for IFR operations in Class G airspace.
IFR clearances always contain:
· A clearance limit (usually the destination);
· Route of flight;
· Altitude assignment; and
· Departure instructions (could be a DP).
The words "cleared as filed" replace only the route of flight portion of a normal clearance. The controller will still state the destination airport, the enroute altitude (or initial altitude and expected final altitude) and DP if appropriate. If a STAR is filed on the flight plan, it is considered part of the enroute portion of the flight plan and is included in the term "cleared as filed."
When an ATC clearance has been received, you may not deviate from it (except in an emergency) unless an amended clearance is received. If you are uncertain of the meaning of an ATC clearance or the clearance appears to be contrary to a regulation, you should immediately request a clarification. When you receive a clearance you should always read back altitude assignments, altitude restrictions, and vectors. A Departure Procedure (DP) may contain these elements but they need not be included in the readback unless the ATC controller specifically states them.
At airports with pretaxi clearance delivery, a pilot should call for the clearance 10 minutes prior to the desired taxi time. After receiving clearance on the clearance delivery frequency, the pilot should call ground control for taxi when ready.
Occasionally, an aircraft with an IFR release will be held on the ground for traffic management reasons. The traffic may be too heavy or weather may be causing ATC delays. If this happens to an aircraft waiting for takeoff, it will be given a hold for release instruction.
When ATC can anticipate long delays for IFR aircraft, they will establish gate hold procedures. The idea is to hold aircraft at the gate rather than cause congestion and unnecessary fuel burn on the taxiways while waiting for an IFR release. Ground control will instruct aircraft when to start engines. ATC expects that turbine-powered aircraft will be ready for takeoff as soon as they reach the runway after having been released from gate hold.
When departing uncontrolled airports, IFR flights will often receive a void time with their clearance. The void time is a usually a 30-minute window of time during which the aircraft must takeoff for its IFR clearance to be valid. If unable to comply with the void time, a pilot must receive another clearance with an amended void time.
The flight plan of an airborne IFR aircraft may only be canceled when the aircraft is in VFR weather conditions and outside of Class A airspace.
Takeoff Procedures
Unless otherwise authorized by the FAA, an air carrier flight may not takeoff unless the weather meets the prescribed takeoff minimums for that airport. If takeoff minimums are not published for the airport, the following visibility is required for takeoff:
· For aircraft having two engines or less: 1 statute mile visibility.
· For aircraft having three or more engines: 1/2 statute mile visibility.
If an air carrier flight is going to takeoff from an airport that is not listed in its operations specifications, the pilot must observe the takeoff weather minimums published for that airport. If no takeoff weather minimums are published for that airport, then the pilot must be sure that the ceiling and visibility meet a sliding scale requirement of 800-2 or 900-1-1/2 or 1,000 -1.
Instrument Approaches
This section is limited to rules and procedures common to most, or all approaches, or procedures that may be used in connection with published instrument approaches.
Contact and visual approaches are both IFR authorizations to proceed to an airport visually. A visual approach may be authorized by ATC to reduce pilot or controller workload and to expedite traffic by shortening flight paths to the airport. The weather must be VFR and the pilot must report either the airport or the preceding aircraft in sight. Either the pilot or ATC may initiate a visual approach. A contact approach may be initiated only by the pilot. The weather need not be VFR but the aircraft must be clear of the clouds, have at least 1 mile visibility and be able to proceed to the landing airport visually.
When an airport has ILS or MLS approaches to parallel runways at least 4,300 feet apart, ATC may conduct approaches to both runways simultaneously. The pilots will be informed if simultaneous approaches are in progress. To ensure safe separation between aircraft, radar monitoring is provided on the tower frequency. A pilot must report any malfunctioning aircraft receivers if he/she has been informed that simultaneous approaches are in progress.
Occasionally, a pilot will be asked to fly an instrument approach to a runway and then fly a visual "sidestep" maneuver to land on a parallel runway. This sidestep maneuver should be executed as soon as possible after the runway environment is in sight.
If a pilot is being radar vectored when an approach clearance is received, he/she must maintain the last assigned altitude until the aircraft is established on a segment of a published route or approach procedure unless a different altitude is assigned by ATC. If a flight is being radar vectored to the final approach course and intercepts a published portion of the course, the pilot may not descend to the published altitudes until cleared for the approach. If a flight has not been cleared for approach while on a radar vector and it becomes apparent that the current vector will take it across the final approach course, the pilot should advise ATC of the situation. Do not turn to intercept the approach course unless cleared to do so.
Unless ATC issues a clearance otherwise, no pilot may make a procedure turn on an instrument approach if any of the following apply:
· The flight is radar vectored to the final approach course or fix
· The flight makes a timed approach from a holding fix
· The approach procedure specifies "No PT"
When the approach procedure involves a procedure turn, a maximum speed of not greater than 200 KIAS should be observed from first overheading the course reversal IAF through the procedure turn maneuver, to ensure containment with the obstruction clearance area.
Except for Category II and III approaches, if RVR minimums for takeoff or landing are prescribed in an instrument approach procedure, but the RVR is not reported for the runway intended, the ground visibilities may be substituted. These may be found in FAA Legend 7.
A pilot may not continue an approach past the final approach fix or on to the final approach segment unless the latest weather report for the airport indicates that the visibility is equal to, or greater than, the visibility required for the approach procedure. If a pilot has begun the final approach segment and then receives a report of below minimum conditions, he/she may continue the approach to the DH or MDA.
To descend below the published DH or MDA on an instrument approach, one of the following must be distinctly visible and identifiable to the pilot:
· Approach light system, except that the pilot may not descend below 100 feet above the touchdown zone elevation using the approach lights as a reference unless the red terminating bars or red side row bars are also distinctly visible and identifiable.
· Threshold
· Threshold markings
· Threshold lights
· Runway end identifier lights
· Visual approach slope indicator
· Touchdown zone or touchdown zone markings
· Touchdown zone lights
· Runway or runway markings
· Runway lights
A pilot must initiate a missed approach from an ILS upon arrival at the DH on the glide slope if none of the required visual references is distinctly visible. If visual contact is lost anytime after descending below the DH but before touchdown, the pilot must start a missed approach.
If a pilot loses visual reference while circling to land from an instrument approach, he/she should follow the missed approach procedure published for the approach used. The pilot should make an initial climbing turn toward the landing runway to establish the aircraft on the missed approach course.
An Airport Surveillance Radar (ASR) approach is one in which an ATC radar controller provides directional guidance and distance to the runway information to the pilot. The only airborne equipment required is an operating radio receiver. The controller will tell the pilot when the aircraft is at the missed approach point and give missed approach instructions as required. If the pilot desires to execute a missed approach prior to the missed approach point, he/she should inform the controller, who will then issue missed approach instructions.
Landing
Except for emergencies, the landing priority of aircraft arriving at a tower controlled airport is on "first-come, first-served" basis. When landing at a tower controlled airport, an aircraft should exit the runway at the first suitable taxiway and remain on the tower frequency until instructed to do otherwise. The aircraft should not turn onto any other taxiway unless a clearance to do so has been received.
If a flight is making an IFR approach at an uncontrolled airport, radar service will be terminated when the aircraft lands or when the controller tells the pilot to change to advisory frequency. After changing to the advisory frequency, the pilot should broadcast his/her intentions and continually update position reports. The advisory frequency will be an FSS frequency, or if there is no FSS on the field, a UNICOM frequency.
ATC furnishes pilots' braking action reports using the terms "good," "fair," "poor" and "nil." If you give a braking action report to ATC, you should use the same terminology.
Communications
The "Sterile Cockpit" Rule: Regulations say only those duties required for the safe operation of the aircraft are allowed during critical phases of flight. Critical phases of flight are defined as climb and descent when below 10,000 feet, taxi, takeoff, and landing. Excluded from the definition of critical phase of flight are any operations at or above 10,000 feet and cruise flight below 10,000 feet. Activities which are prohibited during critical phases of flight include filling out logs, ordering galley supplies, making passenger announcements or pointing out sights of interest. Activities such as eating meals or engaging in nonessential conversations are also prohibited.
The following should be reported without ATC request.
· Vacating a previously assigned altitude for a newly assigned one.
· An altitude change when operating under a VFR-On-Top clearance.
· When unable to climb or descend at a rate of at least 500 feet per minute.
· When an approach has been missed.
· A change in cruising true airspeed of 10 knots or 5%, whichever is greater.
· The time and altitude (or Flight Level) upon reaching a holding fix or clearance limit.
· When leaving an assigned holding fix or point.
· The malfunction of navigation, approach or communication equipment.
· Any information pertaining to the safety of flight.
In addition to the reports listed above, when not in radar contact a pilot must report:
· When over designated compulsory reporting points.
· When leaving the final approach fix inbound on an instrument approach.
· When it becomes apparent that an estimate of arrival time over a fix is in error by more than 3 minutes.
Occasionally an ATC controller will query a pilot about the aircraft's altitude or course. For example, a controller says "Verify 9000," meaning he/she wants confirmation that the aircraft is at 9,000 feet altitude. If the aircraft is not at that altitude, the pilot should reply, "Negative, maintaining 8,000 as assigned." No climb or descent should be started unless specifically assigned by the controller.
Pilots should notify controllers on initial contact that they have received the ATIS broadcast by repeating the alphabetical code word appended to the broadcast. For example, "Information Sierra received."
Speed Adjustments
ATC controllers often issue speed adjustments to radar controlled aircraft to achieve or maintain the desired separation. The following minimum speeds are usually observed:
· Turbine-powered aircraft below 10,000 feet: 210 knots.
· Turbine-powered aircraft departing an airport: 230 knots.
If an ATC controller assigns a speed which is too fast or too slow for the operating limitations of the aircraft under the existing circumstances, the pilot should advise ATC of the speed that will be used. The controller will then issue instructions based on that speed.
Because of the great differences in speed and operating characteristics of helicopters and airplanes, they are usually assigned different routing. Occasionally, larger/faster helicopters are integrated with fixed-wing aircraft. These situations could occur on IFR flights, routes that avoid noise-sensitive areas, or when the helicopter is assigned runways or taxiways to avoid downwash in congested areas.
Holding
Holding may be necessary when ATC is unable to clear a flight to its destination. VORs, non-directional beacons, airway intersections, and DME fixes may all be used as holding points. Flying a holding pattern involves two turns and two straight-and-level legs.
At and below 14,000 feet MSL (no wind), the aircraft flies the specified course inbound to the fix, turns to the right 180°, flies a parallel course outbound for 1 minute, again turns 180° to the right, and flies 1 minute inbound to the fix. Above 14,000 feet MSL, the inbound leg length is 1-1/2 minutes. If a nonstandard pattern is to be flown, ATC will specify left turns.
When 3 minutes or less from the holding fix, the pilot is expected to start a speed reduction so as to cross the fix at or below the maximum holding airspeed. For all aircraft between MHA (minimum holding altitude) and 6,000 feet MSL, holding speed is 200 KIAS. For all aircraft between 6,001 and 14,000 feet MSL, holding speed is 230 KIAS. For all aircraft 14,000 feet MSL and above, holding speed is 265 KIAS. Exceptions to these speeds will be indicated by an icon.
The aircraft is in a holding pattern as of the initial time of arrival over the fix, and that time should be reported to ATC. The initial outbound leg is flown for 1 minute at or below 14,000 feet MSL. Subsequently, timing of the outbound leg should be adjusted as necessary to arrive at the proper inbound leg length. Timing of the outbound leg begins over or abeam the fix, whichever occurs later. If the abeam position cannot be determined, start timing when the turn to outbound is completed. The same entry and holding procedures apply to DME holding, except distance in nautical miles are used to establish leg length.
The FAA has three recommended methods for entering a holding pattern. An aircraft approaching from within sector (A) would fly a parallel entry by turning left to parallel the outbound course, making another left turn to remain in protected airspace, and returning to the holding fix. Aircraft approaching from sector (B) would fly a teardrop entry, by flying outbound on a track of 30° or less to the holding course, and then making a right turn to intercept the holding course inbound to the fix. Those approaching from within sector (C) would fly a direct entry by turning right to fly the pattern.
If the holding pattern is charted, the controller may omit all holding instructions, except the holding direction and the statement "as published." Pilots are expected to hold in the pattern depicted even if it means crossing the clearance limit. If the holding pattern to be used is not depicted on charts, ATC will issue general holding instructions. The holding clearance will include the following information: direction of holding from the fix in terms of the eight cardinal compass points; holding fix; radial, course, bearing, airway, or route on which the aircraft is to hold; leg length in miles if DME or RNAV is to be used; direction of turn if left turns are to be made; time to expect further clearance and any pertinent additional delay information.
Charts
The pilot-in-command must ensure that the appropriate aeronautical charts are on board the aircraft for each flight.
There are a number of questions that require reference to a segment of the Airport/Facility Directory. The legend for this publication is available in the FAA Legends 13 through 19.
Most of the questions concerning interpretation of Approach Charts, DPs and STARs can be answered by referring to the appropriate legend. These legends are available during the test in FAA Legend 40.
There are a few questions that require you to interpret the symbology on Enroute Charts. Unlike the other charts, no legend is available in the test book.
Departure Procedures (DPs) are depicted in one of two basic forms. Pilot Navigation (Pilot NAV) DPs are established where the pilot is primarily responsible for navigation on the DP route. Vector DPs are established where ATC will provide radar navigational guidance to an assigned route or fix. A vector DP will often include procedures to be followed in the event of a two-way communication radio failure.
Standard Terminal Arrival Routes (STARs) are ATC-coded IFR arrival routes established for certain airports. STARs purpose is to simplify clearance delivery procedures. ATC will assign a STAR to a civil aircraft whenever they deem it appropriate.
A few RNAV approaches based on LORAN-C have been established around the country. This approach is flown just like any other nonprecision instrument approach procedure.
The Jet Route system consists of jet routes established from 18,000 feet MSL to FL450 inclusive.
The GPS Approach Overlay Program permits pilots to use GPS avionics under IFR for flying existing instrument approach procedures, except localizer (LOC), localizer directional aid (LDA), and simplified directional facility (SDF) procedures. Aircraft navigating by GPS are considered to be RNAV aircraft. Therefore, the appropriate equipment suffix must be included in the ATC flight plan. The word "or" in the approach title indicates that approach is in Phase III of the GPS Overlay Program. This allows the approach to be flown without reference of any kind to the ground-based NAVAIDs associated with the approach. When using GPS for the approach at the destination airport, the alternate must be an approach other than a GPS or LORAN-C.
Airline transport Pilot Preparation : Weight and Balance
Weight and Balance
Center of Gravity Computation
The first step in the solution of any weight and balance problem is the calculation of the total weight of the aircraft (gross weight) and the total moment. All weight and balance problems on the ATP-121 test use a moment index rather than the actual moment. The moment index is the actual moment divided by 1,000. Questions 8697 through 8711 require the calculation of the total weight and moment index for a Boeing 727-type aircraft. To determine the total weight and moment index, a separate weight and moment must be calculated for the Basic Operating Weight, the passenger loads in the forward and aft passenger compartments, the cargo loads in the forward and aft cargo compartments, and the fuel loads in fuel tanks 1, 2, and 3. The following example references Question 8697.
Basic Operating Weight (BOW) is defined as the empty weight of the aircraft plus the weight of the required crew, their baggage and other standard items such as meals and potable water. The BOW and the Basic Operating Index (Moment/1,000) are the same for all questions. The BOW is 105,500 pounds and the Basic Operating Index is 92,837. See FAA Figure 79.
The number of passengers is stated for each question. For example, Question 8697 refers to Load Condition WT-1. (See FAA Figure 76.) Load Condition WT-1 states that there are 18 passengers in the forward compartment and 95 passengers in the aft compartment. The weight of the passengers can be determined by use of the Passenger Loading Table in the upper left-hand corner of FAA Figure 80. Since neither 18 passengers for the forward compartment nor 95 passengers for the aft compartment is listed in the table, the weight must be calculated by multiplying the number of passengers times the average weight per passenger. A quick examination of the table reveals that the average passenger weight is 170 pounds. The weights are:
FWD Comp = 18 x 170 lbs = 3,060 lbs
AFT Comp = 95 x 170 lbs = 16,150 lbs
The Moment Index (MOM/1,000) is calculated by using the formula:
Weight x Arm/1,000 = MOM/1,000
The arms for the passenger compartments are listed at the top of each of the compartment loading tables after the words, "Forward Compartment Centroid" and "Aft Compartment Centroid." The arm for the forward compartment is 582.0 inches, and the aft compartment arm is 1028.0 inches. The easiest way to apply the 1,000 reduction factor is to move the decimal on the arm three places to the left (i.e., 582.0"/1,000 = .582). In the example used, the Moment/1,000 for the forward and aft passengers compartments (rounded to the nearest whole number) are:
FWD Comp Moment/1,000 = 3,060 x .582 = 1,781
AFT Comp Moment/1,000 = 16,150 x 1.028 = 16,602
The weights for the forward and aft cargo holds are stated for each question. For example, Load Condition WT-1 states that there is 1,500 pounds in the forward hold and 2,500 pounds in the aft hold. The Moment/1,000 can be determined from the tables in the upper right-hand corner of FAA Figure 80. For example, the Moment/1,000 for 1,500 pounds in the forward cargo hold is determined by adding the Moment/1,000 for 1,000 pounds (680) and the Moment/1,000 for 500 pounds (340). If necessary, the Moment/1,000 can also be determined by multiplying weight times arm (divided by 1,000). The Moment/1,000 for the cargo holds are:
FWD Hold = 1,020
AFT Hold = 2,915
Fuel tanks 1 and 3 are the wing tanks and are always loaded with the same weight of fuel. They will always have the Moment/1,000 as well. The number 2 tank is the center fuselage tank and will often have a fuel weight different from tanks 1 and 3. It will always have a different Moment/1,000. For example, Load Condition WT-1 states that the fuel load in tanks 1 and 3 is 10,500 pounds each and that the load in tank 2 is 28,000 pounds. The Moment/1,000 for each tank is determined from the table in the bottom portion of FAA Figure 80. The Moment/1,000 can be calculated, if necessary, by multiplying weight times arm (divided by 1,000). Notice that the arm varies with the fuel load in each tank. The Moment/1,000 for each tank is:
Tank 1 Moment/1,000 = 10,451
Tank 3 Moment/1,000 = 10,451
Tank 2 Moment/1,000 = 25,589
The total weight and total Moment/1,000 is the sum of all the items discussed above. The Total Weight and Moment/1,000 for Load Condition WT-1 is:
Weight Moment/1,000
BOW 105,500 92,837
18 PAX FWD 3,060 1,781
95 PAX AFT 16,150 16,602
FWD Cargo 1,500 1,020
AFT Cargo 2,500 2,915
Fuel Tank 1 10,500 10,451
Fuel Tank 3 10,500 10,451
Fuel Tank 2 + 28,000 + 25,589
Total 177,710 161,646
The Center of Gravity (CG) in inches aft of the Datum line can be determined by using the formula:
CG = Total Moment / Total Weight
Since these questions use a Moment Index instead of Moment, it is necessary to modify this formula by multiplying the (Total Moment/Total Weight) by the reduction factor (1,000). The formula then becomes:
CG = (Total Moment Index / Total Weight) x 1,000
Using the weight and Moment/1,000 we calculated above:
CG = (161,646/177,710) x 1,000 = 909.6 inches
The Center of Gravity of a properly loaded airplane must always fall somewhere along the Mean Aerodynamic Chord (MAC). The CG is often expressed as a percent of MAC. If the CG was at the Leading Edge of MAC (LEMAC), it would be at 0% of MAC. If it were at the Trailing Edge of MAC (TEMAC), it would be at 100% of MAC. The CG's percent of MAC is calculated by:
1. Determine the CG in inches aft of LEMAC by subtracting the distance Datum to LEMAC from the CG in inches aft of Datum. The distance from Datum to LEMAC is given in FAA Figure 79 as 860.5 inches. This is used for all calculations of percent of MAC for the 727. The CG in inches aft of Datum is calculated in the previous paragraph. Using those numbers:
CG (inches aft of LEMAC) = 909.6" - 860.5" = 49.1 inches
2. Determine the CG in percent of MAC by dividing the CG in inches aft of LEMAC by the length of MAC. The length of MAC is distance in inches from LEMAC to TEMAC. It is given in FAA Figure 79 and is 180.9 inches. The formula is:
CG (% of MAC) = (CG in inches aft of LEMAC ÷ MAC) x 100%
Using the numbers from above:
CG (% of MAC) = (49.1" ÷ 180.9") x 100% = 27.1%
Stabilizer Trim Setting
The correct horizontal stabilizer trim setting is very critical for proper takeoff performance of jet aircraft. The main determinants are the CG location and possibly the flap setting. Some aircraft, such as the DC-9, have their stabilizer trim indicators calibrated in percent of MAC, so it is necessary to calculate the CG to know the trim setting. Other aircraft (such as the B-737 and B-727) have their trim indicators marked off in units of nose up trim. In such cases it is necessary to refer to the trim table to determine the proper setting for a given CG. See FAA Figure 55.
The Stab Trim Setting Table at the bottom left side of FAA Figure 55 is used to determine the takeoff trim setting for a B-737. CG location in percent of MAC is used to determine the setting. For example, if the CG is at 8.0% of MAC, the stab trim setting is 7-3/4 units ANU (Airplane Nose Up).
The Stab Trim Setting Table at the left side of FAA Figure 83 is used to determine the takeoff trim setting for a B-727. Flap setting and CG location in percent of MAC are used to determine the setting. For example, if the CG is at 28% of MAC and the flaps are set at 15°, the stab trim setting is 4-1/2 units ANU.
Changing Loading Conditions
Anytime weight is either added to or subtracted from a loaded airplane, both the gross weight and the center of gravity location will change. The solution of such a problem is really a simplified loading problem. Instead of calculating a weight and moment for every section of the aircraft, it is only necessary to compute the original weight and moment and then the effect the change in weight had. Often in these problems the original CG is expressed in percent of MAC and it is necessary to convert this to an arm for the entire aircraft. The following example references Question 8578.
It is sometimes necessary to convert a CG position expressed in percent of MAC to the CG in inches aft of Datum. This is just the reverse of the process described above. This is done in two steps.
1. Convert the CG in percent of MAC to CG in inches aft of LEMAC. This is done by using the formula:
CG (inches aft of LEMAC) = (CG % of MAC ÷ 100%) x MAC.
Load Condition WS-1 (FAA Figure 44) gives a CG of 22.5% and a length of MAC of 141.5 inches. The formula is:
CG (inches aft of LEMAC) = (22.5% ÷ 100%) x 141.5" = 31.84 inches.
2. Add the CG in inches aft of LEMAC to the Distance from Datum to LEMAC. In FAA Figure 44, LEMAC is 549.13 inches aft of Datum.
CG (inches aft of Datum) = 549.13" + 31.84" = 580.97 inches.
Use Question 8578 and Conditions WS-1 (FAA Figure 44) for this example. Use the original weight and CG to calculate the original Moment/1,000. Next use the weight change and station to determine the Moment/1,000 change.
Weight Moment/1,000
Original Weight 90,000 52,287.08
Weight Change - 2,500 - 880.25
New Weight 87,500 51,406.83
Note: A reduction in weight results in a reduction in Moment/1,000. An increase in weight results in an increase in Moment/1,000.
Determine the new CG:
CG = (51,406.83 ÷ 87,500) x 1,000 = 587.51 inches
Convert CG to percent of MAC:
CG (inches aft of LEMAC) = 587.51" - 549.13" = 38.38"
CG (% of MAC) = (38.38" ÷ 141.5") x 100% = 27.1%
When a portion of an aircraft's load is shifted from one location to another, the CG of the loaded aircraft will change as well. Also, the CG will follow the weight. That is, if weight is shifted rearward, the CG will move rearward as well; and if weight is shifted forward, the CG will move forward. To calculate the effect of a weight shift on CG position, three numbers must be known: the weight shifted, the distance the weight was moved, and the total weight of the aircraft. The formula used is:
Change in CG = (Weight Shifted x Distance Shifted) ÷ Total Weight
Question 8573 asks what the effect on CG is if weight is shifted from the forward to aft cargo compartment under Load Condition WS-1 (See FAA Figure 44). Load Condition WS-1 gives the total weight as 90,000 pounds and the weight shifted as 2,500 pounds. The distance shifted is the difference between the forward compartment centroid (352.1 inches) and the aft compartment centroid (724.9 inches), which is 372.8 inches (724.9 - 352.1).
Note: These centroids are distances aft of the Datum line. The index arms are distances from the CG Index and will be discussed in a later example. Notice however, that the difference between the two index arms is also 372.8 inches (144.9 - (-227.9) = 372.8). The solution is:
Change in CG = (2,500 lbs x 372.8") ÷ 90,000 lbs = 10.4"
If weight is shifted forward, the CG will move forward as well. This is expressed by writing the distance shifted as a negative number. If weight is shifted from the aft to the forward cargo compartment, the distance shifted is -372.8 inches. For example, Question 8574 asks about such a shift of 1,800 pounds with an aircraft total weight of 85,000 pounds. The formula is:
Change in CG = (1,800 lbs x (-372.8)) ÷ 85,000 lbs = -7.89"
Questions 8573 and 8576 require an answer in percent of MAC. The change in CG can be converted to a percent of MAC by using the formula:
Change in CG (% of MAC) = (Change in CG/MAC) x 100%
Questions 8577 through 8581 express CG as an Index Arm. Index Arm is the distance, in inches, from an index set at a point close to the normal CG location. A positive Index Arm is a point aft of the index and a negative Index Arm is a point forward of the index. For example, FAA Figure 44 shows LEMAC as having an Index Arm of -30.87 inches or 30.87 inches forward of the index. The index point for all questions on this test is 580.0 inches. CG in Index Arm is calculated by the formula:
CG (Index Arm) = CG (inches aft of Datum) - 580 inches
Using the data from Load Condition WS-5, the formula is:
CG (Index Arm) = 585.21" - 580" = +5.21 inches
Questions 8429 through 8433 require calculation of the maximum weight that can be carried on a pallet. The limiting factor is the amount of weight that the aircraft floor can support per square foot. The calculation refers to FAA legends and involves the following steps:
1. Determine the area covered by the pallet. This is done by multiplying the pallet width by length. Since the pallet dimensions are in inches and the floor load limit is expressed in square feet, it is necessary to convert the pallet area from square inches to square feet. This is done by dividing by 144 (there are 144 square inches in a square foot). The formula is:
Pallet Area (square feet) = (Width x Length) ÷ 144
Using the example of Question 8429 which is a pallet 76" x 76", the area covered is:
Pallet Area = (76" x 76") ÷ 144 = 40.11 square feet
2. Determine the floor load limit by multiplying the pallet area in square feet times the floor load limit per square foot. Again using the example of Question 8429, if the floor load limit is 186 lbs/sq ft:
Floor Load Limit = 40.11 sq ft x 186 lbs/sq ft = 7,460.7 pounds
3. Determine the cargo weight which can be placed on the pallet by subtracting the weight of the pallet and tie-down devices. Since the floor has to support the pallet and tiedown weight, this reduces the total cargo which can be placed on the pallet. Once again, using the example of Question 8429, where the pallet weighs 93 pounds and the tiedown devices weigh 39 pounds (132 pounds total):
Allowable Weight = 7,460.7 lbs - 132 lbs = 7,328.7 pounds
Beech 1900 Weight and Balance
Note: By definition, "Basic Empty Weight" does not include crew weight, so you must include crew in the calculation. By definition, "Basic Operating Weight" includes crew weight so you do not include crew in the calculation.
Helicopter Weight and Balance: CG Shifts
These questions require a re-computation of CG based on a shift of weight only, i.e., CG will change but total weight does not change. AC 91-23A, Chapter 5 gives us a formula for working this type of problem.
Weight Shifted Change of CG
Total Weight = Distance of Shift
These problems may also be worked with a flight computer as shown in AC 91-23A, Chapter 5 in the following manner:
1. Set Weight Shifted (mile scale) over Total Weight (minute scale).
2. Find the Change in CG on the mile scale over the distance shifted on the minute scale.
Question 8518 is solved using both methods.
Helicopter Weight and Balance: Load Limits
In these questions, it will be necessary to compute both a takeoff and a landing weight and balance. Since the stations (CG) for fuel vary with weight, the most simple method of solving these problems is to compute the zero fuel weight for the given conditions, then perform a separate weight and balance for takeoff and landing. Some moments are given; others are not and therefore must be computed. Also, the fuel is stated in gallons, not pounds, which can be converted using the Jet A Table (FAA Figure 33).
Helicopter Weight and Balance: Lateral CG
These questions are answered by using the formula given in AC 91-23A.
1. For shifted weight:
Weight Shifted (WS) CG Shift (CS)
Total Weight (TW) = Distance Shifted (DS)
2. For added/removed weight (WA or WR):
(WA or WR) CG Shift (CS)
New Total Weight (NTW) = Distance shifted (DS)
Refer to answers to Questions 8523 through 8527 for total weights.
Floor Loading Limits
In addition to ensuring that an aircraft is loaded within its weight and balance limits, it is important to make sure that the floor of a cargo compartment is not overloaded. The load limit of a floor is stated in pounds per square foot. The questions on the test require you to determine the maximum load that can be placed on a pallet of certain dimensions.
For example: what is the maximum weight that may be carried on a pallet which has the dimensions of 37 x 39 inches, when the floor load limit is 115 pounds per square foot, the pallet weight is 37 pounds, and the weight of the tiedown devices is 21 pounds?
The first step is to determine the area of the floor (in square feet) covered by the pallet. This is done by multiplying the given dimensions (which calculates the area in square inches) and dividing by 144 (which converts the area to square feet).
37 inches x 39 inches ÷ 144 square inches = 10.02 square feet.
The next step is to determine the total weight that the floor under the pallet can support, by multiplying the area times the floor load limit given in the question.
10.02 square feet x 115 pounds per square foot = 1,152.39 pounds.
The final step is to determine the maximum weight which can be placed on the pallet by subtracting the weight of the pallet and the tiedown devices from the total load limit.
1,152.39 pounds - 58 pounds = 1,094.39 pounds.
The weight on the pallet must be equal to or less than this number (1,094.39, in this example). If it is more than this number, the combination of cargo, pallet, and tiedown weight would exceed the floor load limit. A review of the test questions reveals that the closest answer choice is always equal to or slightly less than the floor limit. All the calculations in this section were performed with a calculator carrying all digits to the right of the decimal point forward for the next step of the problem. The explanations show only two places to the right of the decimal.
A variation of the pallet loading problem is to determine the minimum floor load limit (in pounds per square foot) required to carry a particular loaded pallet. For example: what is the minimum floor load limit to carry a pallet of cargo with a pallet dimension of 78.9 inches x 98.7 inches, and a combination weight of pallet, cargo, and tiedown devices of 9,896.5 pounds?
The first step is to determine the floor area, multiplying the dimensions and dividing by 144 (78.9 x 98.7 ÷ 144 = 54.08 square feet). The second step is to determine the minimum required floor limit by dividing the total weight of the pallet, cargo, and tiedowns by the pallet area (9,896.5 ÷ 54.08 = 183.00 pounds). The correct answer must be at or above this weight (183.00 pounds, in this example).
Center of Gravity Computation
The first step in the solution of any weight and balance problem is the calculation of the total weight of the aircraft (gross weight) and the total moment. All weight and balance problems on the ATP-121 test use a moment index rather than the actual moment. The moment index is the actual moment divided by 1,000. Questions 8697 through 8711 require the calculation of the total weight and moment index for a Boeing 727-type aircraft. To determine the total weight and moment index, a separate weight and moment must be calculated for the Basic Operating Weight, the passenger loads in the forward and aft passenger compartments, the cargo loads in the forward and aft cargo compartments, and the fuel loads in fuel tanks 1, 2, and 3. The following example references Question 8697.
Basic Operating Weight (BOW) is defined as the empty weight of the aircraft plus the weight of the required crew, their baggage and other standard items such as meals and potable water. The BOW and the Basic Operating Index (Moment/1,000) are the same for all questions. The BOW is 105,500 pounds and the Basic Operating Index is 92,837. See FAA Figure 79.
The number of passengers is stated for each question. For example, Question 8697 refers to Load Condition WT-1. (See FAA Figure 76.) Load Condition WT-1 states that there are 18 passengers in the forward compartment and 95 passengers in the aft compartment. The weight of the passengers can be determined by use of the Passenger Loading Table in the upper left-hand corner of FAA Figure 80. Since neither 18 passengers for the forward compartment nor 95 passengers for the aft compartment is listed in the table, the weight must be calculated by multiplying the number of passengers times the average weight per passenger. A quick examination of the table reveals that the average passenger weight is 170 pounds. The weights are:
FWD Comp = 18 x 170 lbs = 3,060 lbs
AFT Comp = 95 x 170 lbs = 16,150 lbs
The Moment Index (MOM/1,000) is calculated by using the formula:
Weight x Arm/1,000 = MOM/1,000
The arms for the passenger compartments are listed at the top of each of the compartment loading tables after the words, "Forward Compartment Centroid" and "Aft Compartment Centroid." The arm for the forward compartment is 582.0 inches, and the aft compartment arm is 1028.0 inches. The easiest way to apply the 1,000 reduction factor is to move the decimal on the arm three places to the left (i.e., 582.0"/1,000 = .582). In the example used, the Moment/1,000 for the forward and aft passengers compartments (rounded to the nearest whole number) are:
FWD Comp Moment/1,000 = 3,060 x .582 = 1,781
AFT Comp Moment/1,000 = 16,150 x 1.028 = 16,602
The weights for the forward and aft cargo holds are stated for each question. For example, Load Condition WT-1 states that there is 1,500 pounds in the forward hold and 2,500 pounds in the aft hold. The Moment/1,000 can be determined from the tables in the upper right-hand corner of FAA Figure 80. For example, the Moment/1,000 for 1,500 pounds in the forward cargo hold is determined by adding the Moment/1,000 for 1,000 pounds (680) and the Moment/1,000 for 500 pounds (340). If necessary, the Moment/1,000 can also be determined by multiplying weight times arm (divided by 1,000). The Moment/1,000 for the cargo holds are:
FWD Hold = 1,020
AFT Hold = 2,915
Fuel tanks 1 and 3 are the wing tanks and are always loaded with the same weight of fuel. They will always have the Moment/1,000 as well. The number 2 tank is the center fuselage tank and will often have a fuel weight different from tanks 1 and 3. It will always have a different Moment/1,000. For example, Load Condition WT-1 states that the fuel load in tanks 1 and 3 is 10,500 pounds each and that the load in tank 2 is 28,000 pounds. The Moment/1,000 for each tank is determined from the table in the bottom portion of FAA Figure 80. The Moment/1,000 can be calculated, if necessary, by multiplying weight times arm (divided by 1,000). Notice that the arm varies with the fuel load in each tank. The Moment/1,000 for each tank is:
Tank 1 Moment/1,000 = 10,451
Tank 3 Moment/1,000 = 10,451
Tank 2 Moment/1,000 = 25,589
The total weight and total Moment/1,000 is the sum of all the items discussed above. The Total Weight and Moment/1,000 for Load Condition WT-1 is:
Weight Moment/1,000
BOW 105,500 92,837
18 PAX FWD 3,060 1,781
95 PAX AFT 16,150 16,602
FWD Cargo 1,500 1,020
AFT Cargo 2,500 2,915
Fuel Tank 1 10,500 10,451
Fuel Tank 3 10,500 10,451
Fuel Tank 2 + 28,000 + 25,589
Total 177,710 161,646
The Center of Gravity (CG) in inches aft of the Datum line can be determined by using the formula:
CG = Total Moment / Total Weight
Since these questions use a Moment Index instead of Moment, it is necessary to modify this formula by multiplying the (Total Moment/Total Weight) by the reduction factor (1,000). The formula then becomes:
CG = (Total Moment Index / Total Weight) x 1,000
Using the weight and Moment/1,000 we calculated above:
CG = (161,646/177,710) x 1,000 = 909.6 inches
The Center of Gravity of a properly loaded airplane must always fall somewhere along the Mean Aerodynamic Chord (MAC). The CG is often expressed as a percent of MAC. If the CG was at the Leading Edge of MAC (LEMAC), it would be at 0% of MAC. If it were at the Trailing Edge of MAC (TEMAC), it would be at 100% of MAC. The CG's percent of MAC is calculated by:
1. Determine the CG in inches aft of LEMAC by subtracting the distance Datum to LEMAC from the CG in inches aft of Datum. The distance from Datum to LEMAC is given in FAA Figure 79 as 860.5 inches. This is used for all calculations of percent of MAC for the 727. The CG in inches aft of Datum is calculated in the previous paragraph. Using those numbers:
CG (inches aft of LEMAC) = 909.6" - 860.5" = 49.1 inches
2. Determine the CG in percent of MAC by dividing the CG in inches aft of LEMAC by the length of MAC. The length of MAC is distance in inches from LEMAC to TEMAC. It is given in FAA Figure 79 and is 180.9 inches. The formula is:
CG (% of MAC) = (CG in inches aft of LEMAC ÷ MAC) x 100%
Using the numbers from above:
CG (% of MAC) = (49.1" ÷ 180.9") x 100% = 27.1%
Stabilizer Trim Setting
The correct horizontal stabilizer trim setting is very critical for proper takeoff performance of jet aircraft. The main determinants are the CG location and possibly the flap setting. Some aircraft, such as the DC-9, have their stabilizer trim indicators calibrated in percent of MAC, so it is necessary to calculate the CG to know the trim setting. Other aircraft (such as the B-737 and B-727) have their trim indicators marked off in units of nose up trim. In such cases it is necessary to refer to the trim table to determine the proper setting for a given CG. See FAA Figure 55.
The Stab Trim Setting Table at the bottom left side of FAA Figure 55 is used to determine the takeoff trim setting for a B-737. CG location in percent of MAC is used to determine the setting. For example, if the CG is at 8.0% of MAC, the stab trim setting is 7-3/4 units ANU (Airplane Nose Up).
The Stab Trim Setting Table at the left side of FAA Figure 83 is used to determine the takeoff trim setting for a B-727. Flap setting and CG location in percent of MAC are used to determine the setting. For example, if the CG is at 28% of MAC and the flaps are set at 15°, the stab trim setting is 4-1/2 units ANU.
Changing Loading Conditions
Anytime weight is either added to or subtracted from a loaded airplane, both the gross weight and the center of gravity location will change. The solution of such a problem is really a simplified loading problem. Instead of calculating a weight and moment for every section of the aircraft, it is only necessary to compute the original weight and moment and then the effect the change in weight had. Often in these problems the original CG is expressed in percent of MAC and it is necessary to convert this to an arm for the entire aircraft. The following example references Question 8578.
It is sometimes necessary to convert a CG position expressed in percent of MAC to the CG in inches aft of Datum. This is just the reverse of the process described above. This is done in two steps.
1. Convert the CG in percent of MAC to CG in inches aft of LEMAC. This is done by using the formula:
CG (inches aft of LEMAC) = (CG % of MAC ÷ 100%) x MAC.
Load Condition WS-1 (FAA Figure 44) gives a CG of 22.5% and a length of MAC of 141.5 inches. The formula is:
CG (inches aft of LEMAC) = (22.5% ÷ 100%) x 141.5" = 31.84 inches.
2. Add the CG in inches aft of LEMAC to the Distance from Datum to LEMAC. In FAA Figure 44, LEMAC is 549.13 inches aft of Datum.
CG (inches aft of Datum) = 549.13" + 31.84" = 580.97 inches.
Use Question 8578 and Conditions WS-1 (FAA Figure 44) for this example. Use the original weight and CG to calculate the original Moment/1,000. Next use the weight change and station to determine the Moment/1,000 change.
Weight Moment/1,000
Original Weight 90,000 52,287.08
Weight Change - 2,500 - 880.25
New Weight 87,500 51,406.83
Note: A reduction in weight results in a reduction in Moment/1,000. An increase in weight results in an increase in Moment/1,000.
Determine the new CG:
CG = (51,406.83 ÷ 87,500) x 1,000 = 587.51 inches
Convert CG to percent of MAC:
CG (inches aft of LEMAC) = 587.51" - 549.13" = 38.38"
CG (% of MAC) = (38.38" ÷ 141.5") x 100% = 27.1%
When a portion of an aircraft's load is shifted from one location to another, the CG of the loaded aircraft will change as well. Also, the CG will follow the weight. That is, if weight is shifted rearward, the CG will move rearward as well; and if weight is shifted forward, the CG will move forward. To calculate the effect of a weight shift on CG position, three numbers must be known: the weight shifted, the distance the weight was moved, and the total weight of the aircraft. The formula used is:
Change in CG = (Weight Shifted x Distance Shifted) ÷ Total Weight
Question 8573 asks what the effect on CG is if weight is shifted from the forward to aft cargo compartment under Load Condition WS-1 (See FAA Figure 44). Load Condition WS-1 gives the total weight as 90,000 pounds and the weight shifted as 2,500 pounds. The distance shifted is the difference between the forward compartment centroid (352.1 inches) and the aft compartment centroid (724.9 inches), which is 372.8 inches (724.9 - 352.1).
Note: These centroids are distances aft of the Datum line. The index arms are distances from the CG Index and will be discussed in a later example. Notice however, that the difference between the two index arms is also 372.8 inches (144.9 - (-227.9) = 372.8). The solution is:
Change in CG = (2,500 lbs x 372.8") ÷ 90,000 lbs = 10.4"
If weight is shifted forward, the CG will move forward as well. This is expressed by writing the distance shifted as a negative number. If weight is shifted from the aft to the forward cargo compartment, the distance shifted is -372.8 inches. For example, Question 8574 asks about such a shift of 1,800 pounds with an aircraft total weight of 85,000 pounds. The formula is:
Change in CG = (1,800 lbs x (-372.8)) ÷ 85,000 lbs = -7.89"
Questions 8573 and 8576 require an answer in percent of MAC. The change in CG can be converted to a percent of MAC by using the formula:
Change in CG (% of MAC) = (Change in CG/MAC) x 100%
Questions 8577 through 8581 express CG as an Index Arm. Index Arm is the distance, in inches, from an index set at a point close to the normal CG location. A positive Index Arm is a point aft of the index and a negative Index Arm is a point forward of the index. For example, FAA Figure 44 shows LEMAC as having an Index Arm of -30.87 inches or 30.87 inches forward of the index. The index point for all questions on this test is 580.0 inches. CG in Index Arm is calculated by the formula:
CG (Index Arm) = CG (inches aft of Datum) - 580 inches
Using the data from Load Condition WS-5, the formula is:
CG (Index Arm) = 585.21" - 580" = +5.21 inches
Questions 8429 through 8433 require calculation of the maximum weight that can be carried on a pallet. The limiting factor is the amount of weight that the aircraft floor can support per square foot. The calculation refers to FAA legends and involves the following steps:
1. Determine the area covered by the pallet. This is done by multiplying the pallet width by length. Since the pallet dimensions are in inches and the floor load limit is expressed in square feet, it is necessary to convert the pallet area from square inches to square feet. This is done by dividing by 144 (there are 144 square inches in a square foot). The formula is:
Pallet Area (square feet) = (Width x Length) ÷ 144
Using the example of Question 8429 which is a pallet 76" x 76", the area covered is:
Pallet Area = (76" x 76") ÷ 144 = 40.11 square feet
2. Determine the floor load limit by multiplying the pallet area in square feet times the floor load limit per square foot. Again using the example of Question 8429, if the floor load limit is 186 lbs/sq ft:
Floor Load Limit = 40.11 sq ft x 186 lbs/sq ft = 7,460.7 pounds
3. Determine the cargo weight which can be placed on the pallet by subtracting the weight of the pallet and tie-down devices. Since the floor has to support the pallet and tiedown weight, this reduces the total cargo which can be placed on the pallet. Once again, using the example of Question 8429, where the pallet weighs 93 pounds and the tiedown devices weigh 39 pounds (132 pounds total):
Allowable Weight = 7,460.7 lbs - 132 lbs = 7,328.7 pounds
Beech 1900 Weight and Balance
Note: By definition, "Basic Empty Weight" does not include crew weight, so you must include crew in the calculation. By definition, "Basic Operating Weight" includes crew weight so you do not include crew in the calculation.
Helicopter Weight and Balance: CG Shifts
These questions require a re-computation of CG based on a shift of weight only, i.e., CG will change but total weight does not change. AC 91-23A, Chapter 5 gives us a formula for working this type of problem.
Weight Shifted Change of CG
Total Weight = Distance of Shift
These problems may also be worked with a flight computer as shown in AC 91-23A, Chapter 5 in the following manner:
1. Set Weight Shifted (mile scale) over Total Weight (minute scale).
2. Find the Change in CG on the mile scale over the distance shifted on the minute scale.
Question 8518 is solved using both methods.
Helicopter Weight and Balance: Load Limits
In these questions, it will be necessary to compute both a takeoff and a landing weight and balance. Since the stations (CG) for fuel vary with weight, the most simple method of solving these problems is to compute the zero fuel weight for the given conditions, then perform a separate weight and balance for takeoff and landing. Some moments are given; others are not and therefore must be computed. Also, the fuel is stated in gallons, not pounds, which can be converted using the Jet A Table (FAA Figure 33).
Helicopter Weight and Balance: Lateral CG
These questions are answered by using the formula given in AC 91-23A.
1. For shifted weight:
Weight Shifted (WS) CG Shift (CS)
Total Weight (TW) = Distance Shifted (DS)
2. For added/removed weight (WA or WR):
(WA or WR) CG Shift (CS)
New Total Weight (NTW) = Distance shifted (DS)
Refer to answers to Questions 8523 through 8527 for total weights.
Floor Loading Limits
In addition to ensuring that an aircraft is loaded within its weight and balance limits, it is important to make sure that the floor of a cargo compartment is not overloaded. The load limit of a floor is stated in pounds per square foot. The questions on the test require you to determine the maximum load that can be placed on a pallet of certain dimensions.
For example: what is the maximum weight that may be carried on a pallet which has the dimensions of 37 x 39 inches, when the floor load limit is 115 pounds per square foot, the pallet weight is 37 pounds, and the weight of the tiedown devices is 21 pounds?
The first step is to determine the area of the floor (in square feet) covered by the pallet. This is done by multiplying the given dimensions (which calculates the area in square inches) and dividing by 144 (which converts the area to square feet).
37 inches x 39 inches ÷ 144 square inches = 10.02 square feet.
The next step is to determine the total weight that the floor under the pallet can support, by multiplying the area times the floor load limit given in the question.
10.02 square feet x 115 pounds per square foot = 1,152.39 pounds.
The final step is to determine the maximum weight which can be placed on the pallet by subtracting the weight of the pallet and the tiedown devices from the total load limit.
1,152.39 pounds - 58 pounds = 1,094.39 pounds.
The weight on the pallet must be equal to or less than this number (1,094.39, in this example). If it is more than this number, the combination of cargo, pallet, and tiedown weight would exceed the floor load limit. A review of the test questions reveals that the closest answer choice is always equal to or slightly less than the floor limit. All the calculations in this section were performed with a calculator carrying all digits to the right of the decimal point forward for the next step of the problem. The explanations show only two places to the right of the decimal.
A variation of the pallet loading problem is to determine the minimum floor load limit (in pounds per square foot) required to carry a particular loaded pallet. For example: what is the minimum floor load limit to carry a pallet of cargo with a pallet dimension of 78.9 inches x 98.7 inches, and a combination weight of pallet, cargo, and tiedown devices of 9,896.5 pounds?
The first step is to determine the floor area, multiplying the dimensions and dividing by 144 (78.9 x 98.7 ÷ 144 = 54.08 square feet). The second step is to determine the minimum required floor limit by dividing the total weight of the pallet, cargo, and tiedowns by the pallet area (9,896.5 ÷ 54.08 = 183.00 pounds). The correct answer must be at or above this weight (183.00 pounds, in this example).
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