Chapter 5


Structure of the Atmosphere

1. How is aircraft performance significantly affected as air becomes less dense? (FAA-H-8083-25)
As air becomes less dense, it reduces
a. Power because the engine takes in less air.
b. Thrust because the propeller is less efficient in thin air.
c. Lift because thin air exerts less force on airfoils.

2. What is the standard atmosphere at sea level? (FAA-H-8083-25)

Standard atmosphere at sea level includes a surface temperature of 59°F or 15°C, and a surface pressure of 29.92 in. Hg or 1013.2 millibars.

3. What are standard atmosphere temperature and pressure lapse rates? (FAA-H-8083-25)

A temperature lapse rate is one in which the temperature decreases at the rate of approximately 3.5°F or 2°C per 1,000 feet up to 36,000 feet. Above this point, the temperature is considered constant up to 80,000 feet. A standard pressure lapse rate is one in which pressure decreases at a rate of approximately 1 in. Hg per 1,000 feet of altitude gain to 10,000 feet.

4. Define the term “Pressure Altitude”. (FAA-H-8083-25)

Pressure altitude is the height above a standard datum plane. An altimeter is a sensitive barometer calibrated to indicate altitude in the standard atmosphere. If the altimeter is set for 29.92 in. Hg Standard Datum Plane (SDP), the altitude indicated is the pressure altitude – the altitude in the standard atmosphere corresponding to the sensed pressure.

5. Why is the pressure altitude important? (FAA-H-8083-25)

Pressure altitude is important as a basis for determining airplane performance as well as for assigning flight levels to airplane operating above 18,000 feet.

6. What are two methods of determining pressure altitude? (FAA-H-8083-25)

Pressure altitude can be determined by either of two methods.
a. By setting the barometric scale of the altimeter to 29.92 and reading the indicated altitude, or
b. By applying a correction factor to the indicated altitude according to the reported “altimeter setting”.

7. Define the term “density altitude”. (FAA-H-8083-25)

Density altitude is pressure altitude corrected for nonstandard temperature. It is the altitude in the standard atmosphere corresponding to a particular value of air density.

8. How does air density affect air performance? (FAA-H-8083-25)

As the density of the air increases (lower density altitude), airplane performance increases and conversely, as air density decreases (higher density altitude), airplane performance decreases. A decrease in air density means a high density altitude; an increase in air density means a lower density altitude.

9. How is density altitude determined? (FAA-H-8083-25)

First find pressure altitude and then correct it for nonstandard temperature variations. Because density varies directly with pressure, and inversely with temperature, a given pressure altitude may exist for a wide range of temperatures. However, a known density occurs for any one temperature and pressure altitude. Regardless of the actual altitude at which the airplane is operating, it will perform as though it were operating at an altitude equal to the exiting density altitude.

10. What factors affect air density? (FAA-H-8083-25)

Air density is affected by changes in altitude, temperature, and humidity. High density altitude refers to thin air while low density altitude refers to dense air. The condition that result in high density altitude are high elevations, low atmospheric pressures, high temperatures, high humidity, or some combination of these factors. Lower elevations, high atmospheric pressure, low temperatures, and low humidity are more indicative of low density altitude.

11. What effect does atmospheric pressure have on air density? (FAA-H-8083-25)
Air density proportional to pressure. If the pressure is doubled, the density is doubled, and if the pressure is lowered, so is the density. This statement is true only at a constant temperature.

12. What effect does temperature have on air density? (FAA-H-8083-25)

Increasing the temperature of a substance decrease its density. Conversely, decreasing the temperature increases the density. Thus, the density of air varies inversely with temperature. This statement is true only at a constant pressure.

13. Since temperature and pressure decreases with altitude, how will air density be affected over all? (FAA-H-8083-25)

The decrease in temperature and pressure have conflicting effects on density as you go up in altitude, but the fairly rapid drop in pressure with increasing altitude is usually the dominating factor. Hence, the density is likely to decrease with altitude gain.

14. What effect does humidity have on air density? (FAA-H-8083-25)

Water vapor is lighter than air, so moist air is higher than dry air. As the water content of the air increases, the air becomes less dense, increasing density altitude and decreasing performance. It is lightest or least dense when it contains the maximum amount of water vapor. Humidity alone is usually not considered an important factor in calculating density altitude and airplane performance, but it does contribute.

15. What is the definition of the term “relative humidity”? (FAA-H-8083-25)

Relative humidity refers to the amount of water vapor in the atmosphere, and is expressed as a percentage of the maximum amount of water vapor the air can hold. This amount varies with the temperature – warm air can hold more water vapor and colder air can hold less.

16. What effect does landing at high-elevation airports have on ground speed with comparable conditions relative to temperature, wind and airplane weight? (FAA-H-8083-25)

Even if you use the same indicated airspeed appropriate for sea level operations, true airspeed is faster, resulting in a faster ground speed (with a given wind condition) throughout the approach, touchdown, and landing roll. This means greater distance to clear obstacles during the approach, a longer ground roll, and consequently the need for a longer runway. All of these factors should be taken into consideration when landing at high-elevation fields, particularly if the field is short.

B. Aircraft Performance

1. What are some of the main elements of aircraft performance? (FAA-H-8083-25)

a. Takeoff and landing distance
b. Rate-of-climb
c. Ceiling
d. Payload
e. Range
f. Speed
g. Maneuverability
h. Stability
i. Fuel economy

2. What is the relationship of lift, weight, thrust and drag in steady, unaccelerated, level flight? (FAA-H-8083-25)

For the airplane to remain in steady, level flight, equilibrium must be obtained by a lift equal to the airplane weight and power plant thrust equal to the airplane drag.

3. What are the two types of drag? (FAA-H-8083-25)

Total drag may be divided into two parts: the wing drag (induced), and drag from everything but the wings (parasite).

4. Define induced drag. (FAA-H-8083-25)

Induced drag is the part of total drag created by the production of lift. Induced drag increases with a decrease in airspeed. The lower the airspeed, the greater the angle of attack required to produce lift equal to the airplane’s weight and therefore the greater the induced drag.

5. Define parasite drag. (FAA-H-8083-25)

Parasite drag is the part of total drag created by the form or shape of airplane parts. It is the sum of pressure and friction drag due to the airplane’s basic configuration and is independent of lift. It is greatest at high airspeeds and is proportional to the square of the airspeed: if the airspeed were doubled, the parasite drag would be quadrupled.

6. How much will drag increase as airplane speed increases? (FAA-H-8083-25)

If an airplane in a steady flight condition at knots is then accelerated to 200 knots, the parasite drag becomes four times as great, but the power required to overcome that drag is eight times the original value. Conversely, when the airplane is operated in steady, level flight at twice as great a speed, the induced drag is one-fourth the original value, and the power required to overcome that drag is only one-half the original value.

7. Discuss the relationship of thrust and power as it relates to airplane climb performance. (FAA-H-8083-25)

Climb depends upon the reserve power or thrust. Reserve power is the available power over and above that required to maintain horizontal flight at a given speed. This, if an airplane is equipped with an engine that produces 200 total available horsepower and the airplane requires only 130 horsepower at a certain level flight speed, the power available for climb is 70 horsepower.

8. Define the term “service ceiling”. (FAA-H-8083-25)

Service ceiling is the maximum density altitude where the best rate-of-climb airspeed will produce a 100 feet-per-minute climb at maximum weight while in a clean configuration with maximum continuous power.

9. Will an aircraft always be capable of climbing to and maintaining its service ceiling? (FAA-H-8083-25)

No. depending on the density altitude, an airplane may not be able to reach it published service ceiling on any given day.

10. What is the definition of “absolute ceiling”? (FAA-H-8083-25)

Absolute ceiling is the altitude at which a climb is no longer possible.

11. What is meant by the terms “power loading” and “wing loading”? (FAA-H-8083-25)

Power loading is expressed in pounds per horsepower and is obtained by dividing the total weight of the airplane by the rated horsepower of the engine. It is a significant factor in the airplane takeoff and climb capabilities.
Wing loading is expressed in pounds per square foot and is obtained by dividing the total weight of the airplane in pounds by the wing area (including ailerons) in square feet. It is the airplane’s wing loading that determines the landing speed.

12. Define the terms “maximum range” and “maximum endurance”. (FAA-H-8083-25)

Maximum range is the maximum distance an airplane can fly for a given fuel supply and is obtained at the maximum lift/drag ratio (L/DMAX). For a given airplane configuration, the maximum lift/drag ratio occurs at a particular angle of attack and lift coefficient, and is unaffected by weight or altitude.
Maximum endurance is the maximum amount of time an airplane can fly for a given fuel supply and is obtained at the point of minimum power required since this would require the lowest fuel flow to keep the airplane in steady, level flight.

13. What is ground effect? (FAA-H-8083-25)

Ground effect occurs due to the interference of the ground surface is flown at approximately one wingspan above the surface. Especially with low-wing aircraft, it is most significant when the airplane is maintaining a constant attitude at low airspeed and low altitude. For example: during landing flare before touchdown, and during takeoff when the airplane lifts off and accelerates to climb speed. A wing in ground effect has a reduction in up wash, down wash, and tip vortices. With reduced tip vortices, induced drag is reduced. When the wing is at a height equal to one-fourth the span, the reduction in induced drag is about 25 percent, and when the wing is at a height equal to one-tenth the span, this reduction is about 50 percent.

14. What major problems can be caused by ground effect? (FAA-H-8083-25)

During landing – At a height of approximately one-tenth of a wing span above the surface, drag may be 50 percent less than when the airplane is operating out of ground effect. Therefore, any excess speed during the landing phase may result in a significant float distance. In such cases, if care is not exercised by the pilot, he/she may run out of runway and options at the same time.
During takeoff – Due to the reduced drag in ground effect, the aircraft may seem capable of takeoff well below the recommended speed. However, as the airplane rises out of ground effect with a deficiency of speed, the greater induced drag may result in very marginal climb performance, or the inability of the airplane to fly at all. In extreme conditions such as high gross weight and high density altitude, the airplane may become airborne initially with a deficiency of speed and then settle back to the runway.

15. What does “flight in the region of normal command” mean?

It means that while holding a constant altitude, a higher airspeed requires a higher power setting, and a lower airspeed requires a lower power setting. The majority of all airplane flying (climb, cruise, and maneuvers) is conducted in the region of normal command.

16. What does “flight in the region of reverse command” mean? (FAA-H-8083-25)

It means that a higher airspeed requires a lower power setting, and a lower airspeed requires a higher power setting to hold altitude. It does not imply that a decrease in power will produce lower airspeed. The region of reversed command is encountered in the low speed phases of flight. Flight speeds below the speed for maximum endurance (lowest point on the power curve) require higher power settings with a decrease in airspeed. Because the need to increase the required power setting with decreased speed is contrary to the “normal command” of flight, flight speeds between minimum required power setting (speed) and the stall speed (or minimum control speed) is termed the region of reversed command. In the region of reversed command, a decrease in airspeed must be accompanied by an increased power setting in order to maintain steady flight.

17. What are examples of where an airplane would be operating in the region of reverse command? (FAA-H-8083-25)

a. An airplane performing a low airspeed, high-pitch altitude, powered approach for a short-field landing.
b. A soft-field takeoff and climb where the pilot attempt to climb out of ground effect without first attaining normal climb pitch attitude and airspeed, is an example of inadvertently operating in the region of reversed-command at a dangerously low altitude.

18. Explain how runway surface and gradient affect performance. (FAA-H-8083-25)

a. Runway surface – Any surface that is not hard and smooth will increase the ground roll during takeoff. This is due to the inability to the tires to smoothly roll along the runway. Although muddy and wet surface conditions can reduce friction between the runway and the tires, they can also act as obstructions and reduce the landing distance.
b. Braking effectiveness – The amount of power that is applied to the brakes without skidding the tires is referred o as braking effectiveness. Ensure that runways are adequate in length for takeoff acceleration and landing deceleration when less than ideal surface conditions are being reported, as it affects braking ability.
c. Runway gradient or slope – A positive gradient indicates that the runway height increases, and a negative gradient indicates that the runway decreases in height. An up sloping runway impedes acceleration and results in a longer ground run during takeoff. However, landing on an up sloping runway typically reduces the landing roll. A down sloping runway aids in acceleration on takeoff resulting in shorter takeoff distances. The opposite is true when landing, as landing on a down sloping runway increases landing distances.

19. What factors affect the performance of an aircraft during takeoffs and landings? (FAA-H-8083-25)

a. Air density (density altitude)
b. Surface wind
c. Runway surface
d. Upslope or down slope of runway
e. Weight
f. Power plant thrust

20. What effects does wind have on aircraft performance? (FAA-H-8083-25)

Takeoff – A headwind increases airplane performance by shortening the takeoff distance and increasing the angle of climb. However, a tailwind decreases performance by increasing the takeoff distance and reducing the angle of climb. The pilot must carefully consider the decrease in airplane performance before attempting a downwind takeoff.
Landing – A headwind increases airplane performance by steepening the approach angle and reducing the landing distance. A tail wind decreases performance by decreasing the approach angle and increasing the landing distance. Again, the pilot must take the wind into consideration prior to landing.
Cruise flight – Winds aloft have a somewhat opposite effect; a headwind decreases performance by reducing ground speed, which in turn increases the fuel requirement for the flight. A tailwind increases performance by increasing the ground speed, which in turn reduces the fuel required for the flight.

21. How does weight affect takeoff and landing performance? (FAA-H-8083-25)

Increased gross weight can produce these effects:
a. Higher liftoff and landing speed required;
b. Greater mass to accelerate or decelerate (slow acceleration / deceleration);
c. Increased retarding force (drag and ground friction); and
d. Longer take off and ground roll.

The effect of gross weight in landing distance is that the airplane will require a greater speed to support the airplane at the landing angle of attack and lift coefficient resulting in an increased landing distance.

22. What effect does an increase in density altitude have on takeoff and landing performance? (FAA-H-8083-25)

An increase in density results in:
a. Increased takeoff distance (greater takeoff TAS required).
b. Reduced rate of climb (decreased thrust and reduced acceleration).
c. Increased true airspeed on approach and landing (same IAS).
d. Increased landing roll distance.
An increase in density altitude (decrease in air density) will increase the landing speed but will not alter the net retarding force. Thus, the airplane will land at the same indicated airspeed as normal but because of reduced air density the true airspeed will be greater. This will result in a longer minimum landing distance.
23. Why does the manufacturer provide various manifold pressure/prop settings for a given power output?

The various power MAP/rpm combinations are provided so the pilot has a choice between operating the aircraft at best efficiency (minimum fuel flow) or operating at best power/speed condition. An aircraft engine operated at higher rpms will produce more friction and, as a result, use more fuel. On the other hand, an aircraft operating at higher and higher altitudes will not be able to continue to produce the same constant power output due to a drop in manifold pressure. The only way to compensate for this is by operating the engine at a higher rpm.

24. What does the term 75% brake horsepower mean? (FAA-H-8083-25)

Brake horsepower (BHP) is the power delivered at the propeller shaft (main drive or main output) of an aircraft engine. 75% BHP means you are delivering 75 percent of the normally rated power or maximum continuous power available at sea level on a standard day to the propeller shaft.

25. Explain how 75%BHP can be obtained from your engine. (FAA-H-8083-25)

Set the throttle (manifold pressure) and propeller (rpm) to the recommended values found in the cruise performance chart of your POH.

26. When would a pilot lean a normally-aspirated direct drive engine? (FAA-P-8740-13)

a. Lean anytime the power setting is 75 percent or less at any altitude.
b. At high-altitude airports, lean for taxi, takeoff, traffic pattern entry and landing.
c. When the density altitude is high (Hot, High, Humid).
d. For landings at airports below 5,000 feet density altitude, adjust the mixture for descent, but only as required.
e. Always consult the POH for proper leaning procedures.

27. What are the different methods available for learning aircraft engines? (FAA-P-8740-13)

Tachometer Method – For best economy operation, the mixture is first leaned from full rich to maximum power (peak rpm), then the leaning process is slowly continued until the engine starts to run rough. Then, enrich the mixture sufficiently to obtain a smoothly firing engine.
Fuel Flow meter Method – Aircraft equipped with fuel flow meters require that you lean the mixture to the published (POH) or marked fuel flow to achieve the correct mixture.
Exhaust Gas Temperature Method – Lean the mixture slowly to establish peak EGT then enrich the mixture by 50° rich (cooler) of peak EGT. This will provide the recommended lean condition for the established power setting.

28. Define the following airplane performance speeds. (FAA-H-8083-25)
Vso – The calibrated power-off stalling speed or the minimum steady flight speed at which the airplane is controllable in the landing configuration.
Vs – The calibrated power-off stalling speed or the minimum steady flight speed at which the airplane is controllable in a specified configuration.
Vy – The calibrated airspeed at which the airplane will obtain the maximum increase in altitude per unit of time. This best rate-of-climb speed normally decreases slightly with altitude.
Vx – The calibrated airspeed at which the airplane will obtain the highest altitude in a given horizontal distance. This best angle-of-climb speed normally increases with altitude.
VLE – The maximum calibrated airspeed at which the airplane can be safely flown with the landing gear extended. This is a problem involving stability and controllability.
VLO – The maximum calibrated airspeed at which the landing gear can be safely extended or retracted. This is a problem involving the air loads imposed on the operating mechanism during extension or retraction of the gear.
VFE – The highest calibrated airspeed permissible with the wing flaps in a prescribed extended position. This is a problem involving the air loads imposed on the structure of the flaps.
VA – The calibrated design maneuvering airspeed. This is the maximum speed at which the limit load can be imposed (either by gusts or full deflection of the control surfaces) without causing structural damage.
VNO –The maximum calibrated airspeed for normal operation or the maximum structural cruise speed. This is the speed above which exceeding the limit load factor may cause permanent deformation of the airplane structure.
VNE – The calibrated airspeed which should never be exceeded. If flight is attempted above this speed, structural damage or structural failure may result.

C. Weight and Balance

1. What performance characteristics will be adversely affected when an aircraft has been overloaded? (FAA-H-8083-25)

a. Higher takeoff speed.
b. Longer takeoff run.
c. Reduced rate and angle of climb.
d. Lower maximum altitude.
e. Shorter range.
f. Reduced cruising speed.
g. Reduced maneuverability.
h. Higher stalling speed.
i. Higher landing speed.
j. Longer landing roll.
k. Excessive weight on the nose wheel.

2. If the weight and balance of an aircraft has changed due to the addition or removal of fixed equipment in the aircraft, what responsibility does the owner or operator have?

The owner or operator of the aircraft should ensure that maintenance personnel make appropriate entries in the aircraft records when repairs or modifications have been accomplished. Weight changes must be accounted for and proper notations made in weight and balance records. The appropriate form for these changes is “Major Repairs and Alterations”. (FAA Form 337).

3. Define the term “ center of gravity” (FAA-H-8083-25)

The center of gravity (CG) is the point about which an aircraft would balance if it were possible to support the aircraft at that point. It is the mass center of the aircraft, or the theoretical point at which the entire weight of the aircraft is assumed to be concentrated. The CG must be within specific limits for safe flight.

4. What effect does a forward center of gravity have on an aircraft’s flight characteristics? (FAA-H-8083-25)

Higher stall speed – Stalling angle of attack reached at a higher speed due to increased wing loading.
Slower cruise speed – Increased drag, greater angle of attack required to maintain altitude.
More stable – The center of gravity is further forward from the center of pressure, which increases longitudinal stability.
Greater back elevator pressure required – Longer takeoff roll, higher approach speeds and problems with the landing flare.

5. What effect does an aft center of gravity have on an aircraft’s flight characteristics? (FAA-H-8083-25)

Lower stall speed – Less wing loading.
Higher cruise speed – Reduced drag, smaller angle of attack required to maintain altitude.
Less stable – Stall and spin recovery more difficult; when angle of attack is increased it tends to result in additional increased angle of attack.

6. Define the following : (FAA-H-8083-25)

Arm – The horizontal distance in inches from the reference datum line to the center of gravity of the item.
Basic empty weight (GAMA) – The standard empty weight plus optional and special equipment that has been installed.
Basic operating weight –The weight of the aircraft, including the crew, ready for flight but without payload and fuel. This term is only applicable to transport aircraft.
Center of gravity – The point about which an aircraft would balance if it were possible to suspend it at that point. Expressed in inches from datum.
Center of gravity limits – The specified forward and aft or lateral points beyond which the CG must not be located during takeoff, flight or landing.
Center of gravity range – The distance between the forward and aft CG limits indicated on pertinent aircraft specifications.
Datum – An imaginary vertical plane or line from which all measurements of arm are taken. Established by the manufacturer.
Empty weight – The airframe, engines, and all items of operating equipment that have fixed locations and are permanently installed in the aircraft. Includes hydraulic fluid, unusable fuel, and un-drainable oil.
Floor load limit – The maximum weight the floor can sustain per square inch / foot as provided by the manufacturer.
Fuel load – The expendable part of the load of the aircraft. It includes only usable fuel, not fuel required to fill the lines or that which remains trapped in the tank sumps.
LEMAC – The leading edge of the mean aerodynamic chord.
Licensed empty weight – The empty weight that consists of the airframe, engine(s), unusable fuel, and un drainable oil plus standard and optional equipment as specified in the equipment list. Some manufacturers used this term prior to GAMA standardization.
Maximum allowable zero fuel weight – The maximum weight authorized for the aircraft not including fuel load. Zero fuel weight for each particular flight is the operating weight plus the payload.
Maximum landing weight – The maximum weight at which the aircraft may normally be landed. The maximum landing weight may be limited to a lesser weight when runway length or atmospheric conditions are adverse.
Maximum ramp weight – The total weight of a loaded aircraft, and includes all fuel. It is greater than the takeoff weight due to the fuel that will be burned during the taxi and run up operations. Ramp weight may also be referred to as taxi weight.
Maximum takeoff weight – The maximum allowable weight at the start of the takeoff run. Some aircraft are approved for loading to a greater weight (ramp or taxi) only to allow for fuel burn off during ground operation. The takeoff weight for a particular flight may be limited to a lesser weight when runway length, atmospheric conditions, or other variables are adverse.
Maximum weight – The maximum authorized weight of the aircraft and all of its equipment as specified in the Type Certificate Data Sheets (TCDS) for the aircraft.
Maximum zero fuel weight (GAMA) – The maximum weight, exclusive of usable fuel.
Mean aerodynamic chord (MAC – The average distance from the leading edge to the trailing edge of the wing. The MAC is specified for the aircraft by determining the average chord of an imaginary wing which has the same aerodynamic characteristics as the actual wing.
Moment – The product of the weight of an item multiplied by its arm. Moments are expressed in pound-inches.
Moment index – A moment divided by a constant such as 100, 1,000, or 10,000. The purpose of using a moment index is to simplify weight and balance computations of large aircraft where heavy items and long arms result in large, unmanageable numbers.
Payload (GAMA) – The weight of occupants, cargo, and baggage.
Ramp or taxi weight – The maximum takeoff gross weight plus fuel to be burned during taxi and run-up.
Standard empty weight (GAMA) – The airframe, engines, and all items of operating equipment that have fixed locations and are permanently installed in the airplane; including fixed ballast, hydraulic fluid, unusable fuel, and full engine oil.
Station – A location in the aircraft which is identified by a number designating its distance in inches from the datum. The datum is, therefore, identified as station zero. The station and arm are usually identical. An item located at station +50 would have an arm of 50 inches.
Useful load – The weight of the pilot, copilot, passengers, baggage, usable fuel and drainable oil. It is the empty weight subtracted from the maximum allowable takeoff weight. The term applied to general aviation aircraft only.
7. What basic equation is used in all weight and balance problems to find the center of gravity location of an airplane and/or its components? (FAA-H-8083-25)

Weight * Arm = Moment

By rearrangement of this equation to the forms:

Weight = Moment / Arm

Arm = Moment / Weight

CG = Moment / Weight

With any two known values, the third value can be found.

Remember : W A M

(Weight * Arm = Moment)

8. What basic equation is used to determine center of gravity? (FAA-H-8083-25)

Center of gravity is determined by dividing total moments by total weight.

9. Explain the term percent of mean aerodynamic chord (MAC). (FAA-H-8083-1)

Expression of the CG relative to the MAC is a common practice in larger aircraft. The CG position is expressed as a percent MAC (percent of mean aerodynamic chord), and the CG limits are expressed in the same manner. Normally, an aircraft will have acceptable flight characteristics if the CG is located somewhere near the 25% average chord point. This means the CG is located one-fourth of the total distance back from the leading edge of the average wing section.

10. If the weight of an aircraft is within takeoff limits but the CG limit has been exceeded, what actions can the pilot take to correct the situation? (FAA-H-8083-25)

The most satisfactory solution to this type of problem is to shift baggage, passengers, or both in an effort to make the aircraft CG fall within limits.

11. What simple and fundamental weight check can e made by all pilots before flight? (FAA-H-8083-25)

A useful load check can be made to determine if the useful load limit has been exceeded. This check may be a mental calculation if the pilot is familiar with the aircraft’s limits and knows that unusually heavy loads are not abroad. The pilot needs to know the useful load limit of the particular aircraft. This information may be found in the latest weight and balance report, in a logbook, or on a Major Repair and Alteration Form located in the aircraft. If the useful load limit is not stated directly, simply subtract the empty weight from the maximum takeoff weight.

12. What factors would contribute to a change in center of gravity location during flight?

The operator’s flight manual should show procedures which fully account for variations in CG travel during flight caused by variables such as the movement of passengers and the effect of the CG travel due to fuel used.

13. If actual weights for weight and balance computations are unknown, what weights may be assumed for weight and balance computations? (FAA-H-8083-1)

Some standard weights used in general aviation are:
Crew and Passengers 170 lbs. /person
Gasoline 6lbs./
Oil 7.5lbs./
Water 8.35lbs./
Note : These weights are not to be used in lieu of available actual weights!

14. How is the CG affected during flight as fuel is used? (FAA-H-8083-25)

As fuel is burned during flight, the weight of the fuel tanks will change and as a result the CG will change. Most aircraft, however, are designed with the fuel tanks positioned close to the CG; therefore, the consumption of fuel does not affect the CG to any great extent. Also, the lateral balance can be upset by uneven fuel loading or burn-off. The position of the lateral CG is not normally computed for an airplane, but the pilot must be aware of the adverse effects that will result from a laterally unbalanced condition.