Chapter 4

Oral Exam Preparation Questions and Answers

The following questions reference the Cessna 152 systems. Be sure to review your aircraft’s AFM or POH.
A. Aircraft and Engine Operations

1. What are the four main control surfaces and what are their functions? (FAA-H-8083-25)

Elevators – The elevators control the movement of the airplane about its lateral axis. This motion is called Pitch.
Ailerons – The ailerons control the airplane’s movement about its longitudinal axis. This motion is called Roll.
Rudder – The rudder controls movement of the airplane about its vertical axis. This motion is called Yaw.
Trim Tabs – Trim tabs are small, adjustable hinged-surface on the aileron, rudder, or elevator control surfaces. They are labor-saving devices that enable pilot to release manual pressure on the primary control.

2. How are the various flight controls operated? (AFM)

The flight control surfaces are manually actuated through use of either a rod or cable system. A control wheel actuates the ailerons and elevator, and rubber/brake pedals actuate the rudder.

3. What are flaps and what is their function? (FAA-H-8083-25)

The wing flaps are movable panels on the inboard trailing edges of the wings. They are hinged so that they may be extended downward into the flow of air beneath the wings to increase both lift and drag. Their purpose is to permit a slower airspeed and a steeper angle of descent during a landing approach. In some cases, they may also be used to shorten the takeoff distance.

4. Describe the landing gear system on this airplane. (AFM)

The landing gear consists of tricycle-type system utilizing two main wheels and a steerable nose wheel. Tubular spring steel main gear struts provide main gear shock absorption, while nose gear shock absorption is provided by a combination air/oil shock strut.

5. Describe the braking system on this aircraft. (AFM)

Hydraulically actuated disc-type brakes are utilized on each main gear wheel. A hydraulic line connects each brake to a master cylinder located on each pilot’s rudder pedals. By applying pressure to the top of either the pilot’s or copilot’s set of rudder pedals, the brakes may be applied.

6. How is steering accomplished on the ground? (AFM)

Light airplanes are generally provided with nose wheel steering capabilities through a simple system of mechanical linkage connected to the rudder pedals. When a rudder pedal is depressed, a spring-loaded bungee (push-pull rod) connected to the pivotal portion of a nose wheel strut will turn the nose wheel.

7. What type of engine does your aircraft have? (AFM)

A horizontally opposed four-cylinder, overhead-valve, air-cooled, carbureted engine. The engine is manufactured by Lycoming and rated at 110 HP.

8. What four strokes must occur in each cylinder of a typical four stroke engine in order for it to produce full power? (FAA-H-8083-25)

The four strokes are:

Intake – fuel mixture is drawn into cylinder by downward stroke
Compression – mixture is compressed by upward stroke
Power – spark ignites mixture forcing piston downward and producing power
Exhaust – burned gases pushed out of cylinder by upward stroke

9. What does the carburetor do? (FAA-H-8083-25)

Carburetion may be defined as the process of mixing fuel and air in the correct proportions so as to form a combustible mixture. The carburetor vaporizes liquid fuel into small particles and then mixes it with air. It measures the airflow and meters fuel accordingly.

10. How does the carburetor heat system work? (AFM)

A carburetor heat valve, controlled by the pilot, allows unfiltered, heated air from a shroud located around an exhaust riser or muffler to be directed to the induction air manifold prior to the carburetor. Carburetor heat should be used anytime suspected or known carburetor icing conditions exist.

11. What change occurs to the fuel / air mixture when applying carburetor heat? (FAA-H-8083-25)

Normally, the introduction of heated air into the carburetor will result in a richer mixture. Warm air is less dense, resulting in less air for the same amount of fuel.

12. What does the throttle do? (FAA-H-8083-25)

The throttle allows the pilot to manually control the amount of fuel / air charge entering the cylinders. This in turn regulates the engine speed and power.

13. What does the mixture control do? (FAA-H-8083-25)

It regulates the fuel-to-air ratio. All airplane engines incorporate a device called a mixture control, by which the fuel / air ratio can be controlled by the pilot during flight. The purpose of a mixture control is to prevent the mixture from becoming too rich at high altitudes, due to decreasing air density. It is also used to lean the mixture during cross-country flights to conserve fuel and provide optimum power.

14. What type of ignition system does your airplane have? (AFM)

Engine ignition is provided by two engine-driven magnetos, and two spark plugs per cylinder. The ignition system is completely independent of the aircraft electrical system. The magnetos are engine-driven self-contained units supplying electrical current without using an external source of current. However, before they can produce current, the magnetos must be actuated, as the engine crankshaft is rotated by some other means. To accomplish this, the aircraft battery furnishes electrical power to operate a starter which, through a series of gears, rotates the engine crankshaft. This in turn actuates the armature of the magneto to produce the sparks for ignition of the fuel in each cylinder. After the engine starts, the starter system is disengaged, and the battery no longer contributes to the actual operation of the engine.

15. What are the two main advantages of a dual ignition system? (FAA-H-8083-25)

a. Increased safety: in case one system fails the engine may be operated on the other until a landing is safely made.
b. More complete and even combustion of the mixture, and consequently, improved engine performance; i.e., the fuel / air mixture will be ignited on each side of the combustion chamber and burn toward the center.

16. What type of fuel system does your aircraft have? (AFM)

The fuel system is a “gravity feed” system. Using gravity, the fuel flows from two wing fuel tanks to a fuel shutoff valve which, in the “on” position, allows fuel to flow through a strainer and then to the carburetor. From there, the fuel is mixed with air and then flows into the cylinders through the intake manifold tubes.

17. What purpose do fuel tank vents have? (AFM)

As the fuel level in an aircraft fuel tank decreases, a vacuum would be created within the tank which would eventually result in a decreasing fuel flow and finally engine stoppage. Fuel system venting provides a way of replacing fuel with outside air, preventing formation of a vacuum.

18. Does your aircraft use a fuel pump? (AFM)

No, the fuel is transferred from the wing tanks to the carburetor by the “gravity feed” system. The gravity system does not require a fuel pump because the fuel is always under positive pressure to the carburetor. For some aircraft where for some reason it is not possible to place the wings above the carburetor, or for which a greater pressure is required than what gravity feed can supply, it is necessary to utilize engine-driven fuel pumps and auxiliary fuel pumps as backups.

19. What type fuel does your aircraft require (minimum octane rating and color)? (AFM)

The approved fuel grade used is 100LL and the color is blue.

20. Can other types of fuel be used if the specified grade is not available? (FAA-H-8083-25)

Airplane engines are designed to operate using a specific grade of fuel as recommended by the manufacturer. If the proper grade of fuel is not available, it is possible, but not desirable, to use the next higher grade as a substitute. Always reference the aircraft’s AFM or POH.

21. What color of dye is added to the following fuel grades: 80, 100, 100LL, Turbine? (FAA-H-8083-25)

Grade Color
80 Red
100 Green
100LL Blue
Turbine Colorless

22. What is the function of the manual primer, and how does it operate? (AFM)

The manual primer’s main function is to provide assistance in starting the engine. The primer draws fuel from the fuel strainer and injects it directly into the cylinder intake ports. This usually results in a quicker, more efficient engine start.

23. Describe the electrical system on your aircraft.

Electrical energy is provided by a 28-volt, direct-current system powered by an engine-driven 60-amp alternator and a 24-volt battery.

24. How are the circuits for the various electrical accessories within the aircraft protected? (AFM)

Most of the electrical circuits in an airplane are protected from an overload condition by wither circuit breakers or fuses except that when an overload occurs, a circuit breaker can be reset.

25. The electrical system provides power for what equipment in an airplane? (AFM)

Normally, the following:
a. Radio equipment
b. Turn coordinator
c. Fuel gauges
d. Pilot heat
e. Landing light
f. Taxi light
g. Strobe lights
h. Interior lights
i. Instrument lights
j. Position lights
k. Flaps (may be)
l. Stall warning system (may be)
m. Oil temperature gauge
n. Electric fuel pump (may be)

26. What does the ammeter indicate? (AFM)

The ammeter indicates the flow of current, in amperes, from the alternator to the battery or from the battery to the electrical system. With the engine running and master switch on, the ammeter will indicate the charging rate to the battery. If the alternator has gone off-line and is no longer functioning, or the electrical load exceeds the output of the alternator, the ammeter indicates the discharge rate of the battery.

27. What function does the voltage regulator have?

The voltage regulator is a device which monitors system voltage, detects changes, and makes the required adjustments in the output of the alternator to maintain a constant regulated system voltage. It must do this at low RPM, such as during taxi, as well as at high RPM in flight. In a 28-volt system, it will maintain 28 volts + / – 0.5 volts.

28. Why is the generator / alternator voltage output slightly higher than the battery voltage? (FAA-H-8083-25)

The difference in voltage keeps the battery charged. For example, a 12-volt battery would be supplied with 14 volts.

29. How does the aircraft cabin heat work? (AFM)

Fresh air, heated by an exhaust shroud, is directed to the cabin through a series of ducts.

30. How does the pilot control temperature in the cabin? (AFM)

Temperature is controlled by mixing outside air (cabin air control) with heated air (cabin heat control) in a manifold near the cabin firewall. This air is then ducted to vents located on the cabin floor.

31. What are the two types of oil available for use in your airplane?

Mineral Oil – Also known as no detergent oil. It contains no additives. This type oil is normally used after an engine overhaul or when an aircraft engine is new, for engine break-in purposes.

Ash less dispersant – Mineral oil with additives. It has high anti-wear properties along with multi-viscosity (ability to perform in a wide range of temperatures). It also picks up contamination and carbon particles and keeps them suspended so that buildings and sludge do not form in the engine.

B. System and Equipment Malfunctions

1. What causes “carburetor icing”, and what are the first indications of its presence? (FAA-H-8083-25)

The vaporization of fuel, combined with the expansion of air as it passes through the carburetor, causes a sudden cooling of the mixture. The temperature of the air passing through the carburetor may drop as much as 60°F within a fraction of a second. Water vapor is squeezed only by this cooling, and if the temperature in the carburetor reaches 32°F or below, the moisture will be deposited as frost or ice inside the carburetor. For airplanes with a fixed-pitch propeller, the first indication of carburetor icing is loss of RPM. For airplanes with controllable-pitch (constant-speed) propellers, the first indication is usually a drop in manifold pressure.

2. What method is used to determine that carburetor ice has been eliminated? (FAA-H-8083-25)

When heat is first applied, there will be a drop in RPM in airplanes equipped with a fixed-pitch propeller; there will be a drop in manifold pressure in airplanes equipped with a controllable-pitch propeller. If ice is present there will be a rise in RPM or manifold pressure after the initial drop (often accompanied by intermittent engine roughness); and then, when the carburetor heat is turned “off”, the RPM or manifold pressure will rise to a setting greater than that before application of heat. The engine should run more smoothly after the ice has been removed.

3. What conditions are favorable for carburetor icing? (FAA-H-8083-25)

Carburetor ice is most likely to occur when temperatures are below 70°F (21°C) and the relative humidity is above 80 percent. However, due to the sudden cooling that takes place in the carburetor, icing can occur even with temperatures as high as 100°F (38°C) and humidity as low as 50 percent. This temperature drop can be as much as 60° to 70° F.

4. What is “Detonation”? (FAA-H-8083-25)

Detonation is an uncontrolled, explosive ignition of the fuel / air mixture within the cylinder’s combustion chamber. It causes excessive temperature and pressure which, if not corrected, can quickly lead to failure of the piston, cylinder, or valves. In less severe cases, detonation causes engine overheating, roughness, or loss of power. Detonation is characterized by high cylinder head temperatures, and is most likely to occur when operating at high power settings.

5. What action should be taken if detonation is suspected? (FAA-H-8083-25)

Corrective action for detonation may be accomplished by adjusting any of the engine controls which will reduce both temperature and pressure of the fuel air charge.
a. Reduce power.
b. Reduce the climb rate for better cooling
c. Enrich the fuel/air mixture.
d. Open cowl flaps if available.
Also, ensure that the airplane has been serviced with the proper grade of fuel.

6. What is “pre-ignition”? (FAA-H-8083-25)

Pre-ignition occurs when the fuel/air mixture ignites prior to the engine’s normal ignition event resulting in reduced engine power and high operating temperatures. Premature burning is usually caused by a residual hot spot in the combustion chamber, often created by a small carbon deposit on a spark plug, a cracked spark plug insulator, or other damage in the cylinder that causes a part to heat sufficiently to ignite the fuel / air charge. As with detonation, pre-ignition may also cause severe engine damage, because the expanding gases exert excessive pressure on the piston while still on its compression stroke.

7. What action should be taken if pre-ignition is suspected? (FAA-H-8083-25)

Corrective actions for pre-ignition include any type of engine operation which would promote cooling such as:
a. Reduce power.
b. Reduce the climb rte of better cooling.
c. Enrich the fuel / air mixture.
d. Open cowl flaps if available.

8. During the before-takeoff run-up, you switch the magnetos from the “BOTH” position to the “RIGHT” position and notice there is no RPM drop. What condition does this indicate?

The left P-lead is not grounding, or the engine has been running only on the right magneto because the left magneto has totally failed.

9. Interpret the following ammeter indications.

a. Ammeter indicates a right deflection (positive).
• After starting – Power from the battery used for starting is being replenished by the alternator; or, if a full-scale charge is indicated for more than 1 minute, the starter is still engaged and a shutdown is indicated.
• During flight – A faulty voltage regulator is causing the alternator to overcharge the battery. Reset the system and if the condition continues, terminate the flight as soon as possible.

b. Ammeter indicates a left deflection (negative).
• After starting – It is normal during start. At other times this indicates the alternator is not functioning or an overload condition exists in the system. The battery is not receiving a charge.
• During flight – The alternator is not functioning or an overload exists in the system. The battery is not receiving a charge. Possible causes: the master switch was accidentally shut off, or the alternator circuit breaker tripped.

10. What action should be taken if the ammeter indicates a continuous discharge while in flight?

The alternate has quit producing a charge, so the alternator circuit breaker should be checked and reset if necessary. If this does not correct the problem, the following should be accomplished:
a. The alternator should be turned off: pull the circuit breaker (the field circuit will continue to draw power from the battery).
b. All electrical equipment not essential to flight should be turned off (the battery is now the only source of electrical power).
c. The flight should be terminated and a landing made as soon as possible.

11. What action should be taken if the ammeter indicates a continuous charge while in flight (more than two needle widths)?

If a continuous excessive rate of charge were allowed for any extended period of time, the battery would overheat and evaporate the electrolyte at an excessive rate. A possible explosion of the battery could be adversely affected by higher than normal voltage. Protection is provided by an over voltage sensor which will shut the alternator down if an excessive voltage is detected. If this should occur the following should be done:
a. The alternator should be turned off; pull the circuit breaker (the field circuit will continue to draw power from the battery).
b. All electrical equipment not essential to flight should be turned off (the battery is now the only source of electrical power).
c. The flight should be terminated and a landing made as soon as possible.

12. During a cross-country flight you notice that the oil pressure is low, but the oil temperature is normal. What is the problem and what action should be taken?

A low oil pressure in flight could be the result of any one of several problems, the most common being that of insufficient oil. If the oil temperature continues to remain normal, a clogged oil pressure relief valve or an oil pressure gauge malfunction could be the culprit. In any case, a landing at the nearest airport is advisable to check for the cause of trouble.

13. What procedures should be followed concerning a partial loss of power in flight? (AFM)

If a partial loss of power occurs, the first priority is to establish and maintain a suitable airspeed (best glide airspeed if necessary). Then, select an emergency landing area and remain within gliding distance. As time allows, attempt to determine the cause and correct it.

Complete the following checklist:
a. Check the carburetor heat.
b. Check the amount of fuel in each tank and switch fuel tanks if necessary.
c. Check the fuel selector valve’s current position.
d. Check the mixture control.
e. Check that the primer control is all the way in and locked.
f. Check the operation of the magnetos in all three positions; both, left or right.

14. What procedures should be followed if an engine fore develops in flight? (AFM)

In the event of an engine fire in flight, the following procedures should be used:
a. Set the mixture control to “Idle cutoff”.
b. Set the fuel selector valve to “Off”.
c. Turn the master switch to “Off”.
d. Set the cabin heat and air vents to “Off”; leave the overhead vents “On”.
e. Establish an airspeed of 100 KIAS and increase the descent, if necessary, to find an airspeed that will provide for an incombustible mixture.
f. Execute a forced landing procedures checklist.

15. What procedures should be followed if an engine fire develops on the ground during starting? (AFM)

Continue to attempt an engine start as a start will cause flames and excess fuel to be sucked back through the carburetor.
a. If the engine starts:
• Increase the power to a higher RPM for a few moments; and
• Shut down the engine and inspect it.
b. If the engine does not start:
• Set the throttle to the “Full” position.
• Set the mixture control to “Idle cutoff”.
• Continue to try an engine start in an attempt to put out the fire by vacuum.
c. If the fire continues:
• Turn the ignition switch to “Off”.
• Turn the master switch to “Off”.
• Set the fuel selector to “Off”.

In all cases, evacuate the aircraft and obtain a fire extinguisher and / or assistance.

C. Pitot / Static Flight Instruments

1. What instruments operate off of the pitot / static system? (FAA-H-8083-15)

Altimeter, Vertical Speed, and Airspeed Indicator.

2. How does an altimeter work? (FAA-H-8083-15)

Aneroid wafers expand and contract as atmospheric pressure changes, and through a shaft and gear linkage, rotate pointers on the dial of the instrument.

3. What are the limitations of a pressure altimeter? (FAA-H-8083-15)

Non standard pressure and temperature; temperature variations expand or contract the atmosphere and raise or lower pressure levels that the altimeter senses.

On a warm day – The pressure level is higher than on a standard day. The altimeter indicates lower than actual altitude.
On a cold day – The pressure level is lower than on a standard day. The altimeter indicates higher than actual altitude.

Changes in surface pressure also affect pressure levels at altitude.

Higher than standard pressure – The pressure level is higher than on a standard day. The altimeter indicates lower than actual altitude.
Lower than standard pressure – The pressure level is lower than on a standard day. The altimeter indicates higher than actual altitude.

Remember : High to low or hot to cold, look out below!

4. Define and state how you would determine the following altitudes. (FAA-H-8083-25)

Indicated Altitude
Pressure Altitude
True Altitude
Density Altitude
Absolute Altitude

Absolute altitude – the vertical distance of an aircraft above the terrain.
Indicated altitude – the altitude read directly from the altimeter (uncorrected) after it is set to the current altimeter setting.
Pressure altitude – the altitude when the altimeter setting window is adjusted to 29.92. Pressure altitude is used for computer solutions to determine density altitude, true altitude, true airspeed, etc.
True altitude – the true vertical distance of the aircraft above sea level. Airport, terrain, and obstacle elevations found on aeronautical charts are true altitudes.
Density altitude – pressure altitude corrected for non-standard temperature variations. Directly related to an aircraft’s take off, climb, and landing performance.

5. How does the airspeed indicator operate? (FAA-H-8083-25)

The airspeed indicator is a sensitive, differential pressure gauge which measures the difference between impact pressure from the pilot head and undisturbed atmospheric pressure from the static source. The difference is registered by the airspeed pointer on the face of the instrument.

6. What is the limitation of the airspeed indicator? (FAA-H-8083-15)

The airspeed indicator is subject to proper flow of air in the pitot / static system.

7. What are the errors of the airspeed indicator?

Position error – Caused by the static ports sensing erroneous static pressure; slipstream flow causes disturbances at the static port preventing actual atmospheric pressure measurement. It varies with airspeed, altitude and configuration, and may be a plus or minus value.

Density error – Changes in altitude and temperature are not compensated for by the instrument.

Compressibility error – Caused by the packing of air into the pitot tube at high airspeeds, resulting in higher than normal indications. It is usually not a factor at slower speeds.

8. What are the different types of aircraft speeds? (FAA-H-8083-15)

Indicated airspeed (IAS) – read off the instrument.
Calibrated airspeed (CAS) – IAS corrected for instrument and position errors; obtained from the Pilot’s Operating Handbook or off the face of the instrument.
Equivalent airspeed (EAS) – CAS corrected for adiabatic compressible flow at altitude.
True airspeed (TAS) – CAS corrected for nonstandard temperature and pressure; obtained from the flight computer. POH or A/S indicator slide computer.
Ground speed (GS) – TAS corrected for wind; speed across ground; use the flight computer.

9. Name several important airspeed limitations not marked on the face of the airspeed indicator. (FAA-H-8083-25)

Maneuvering speed (VA) – the “rough air” speed and the maximum speed for abrupt maneuvers. If rough air or severe turbulence is encountered during flight, the airspeed should be reduced to maneuvering speed or less to minimize the stress on the airplane structure.
Landing Gear Operating speed (VLO)- the maximum speed for extending or retracting the landing gear if using aircraft equipped with retractable landing gear.
Best Angle-of-Climb speed (VX) – important when a short-field takeoff to clear an obstacle is required.
Best Rate-of-Climb speed (Vy) – the airspeed that will give the pilot the most altitude in a given period of time.

10. What airspeed limitations apply to the color-coded marking system of the airspeed indicator? (FAA-H-8083-25)

White Arc Flap operating range
Lower A/S Limit White Arc VSO (stall speed landing configuration)
Upper A/S Limit White Arc VFE(maximum flap extension speed)
Green Arc normal operating range
Lower A/S Limit Green Arc VS1(stall speed clean or specified configuration)
Upper A/S Limit Green Arc VNO(normal operations speed or maximum structural cruise speed)
Yellow Arc Caution Range (operations in smooth air only)
Red Line VNE (maximum speed for operations in smooth air only)

11. How does the vertical speed indicator work? (FAA-H-8083-15)

The vertical speed indicator is a pressure differential instrument. Inside the instrument case is an aneroid very much like the one in an airspeed indicator. Both the inside of this aneroid and the inside of the instrument case are vented to the static system, but the case is vented through a calibrated orifice that causes the pressure inside the case to change more slowly than the pressure inside the aneroid. As the aircraft ascends, the static pressure becomes lower and the pressure inside the case compresses the aneroid, moving the pointer upward, showing a climb and indicating the number of feet per minute the aircraft is ascending.

12. What are the limitations of the vertical speed indicator? (FAA-H-8083-25)

The VSI is not accurate until the aircraft is stabilized. Because of the restriction in airflow to the static line, a 6 to 9 second lag is required to equalize or stabilize the pressures. Sudden or abrupt changes in aircraft attitude will cause erroneous instrument readings as airflow fluctuates over the static port. Both rough control technique and turbulent air result in unreliable needle indications.

D. Gyroscopic Flight Instruments

1. What instruments contain gyroscopes? (FAA-H-8083-25)

a. The turn coordinator
b. The heading indicator (directional gyro)
c. The attitude indicator (artificial horizon)

2. What are the two fundamental properties of a gyroscope? (FAA-H-8083-25)

Rigidity in space – a gyroscope remains in a fixed position if the plane in which it is spinning.
Precession – the tilting or turning of a gyro in response to a deflective force. The reaction to this force does not occur at the point where it was applied; rather, it occurs at a point that is 90° later in the direction of rotation. The rate at which the gyro precesses is inversely proportional to the speed of the rotor and proportional to the deflective force.

3. What are the various power sources that may be used to power the gyroscopic instruments in an airplane? (FAA-H-8083-25)

In some airplanes, all the gyros are vacuum, pressure, or electrically operated: in others, vacuum or pressure systems provide the power for the heading and altitude indicators, while the electrical system provides the power for the turn coordinator. Most airplanes have at least two sources of power to ensure at least one source of bank information if one power source fails.

4. How does the vacuum system operate? (FAA-H-8083-25)

An engine-driven vacuum pump provides suction which pulls air from the instrument case. Normal pressure entering the case is directed against rotor vanes to turn the rotor (gyro) at high speed, much like a water wheel or turbine operates. Air is drawn into the instrument through a filter from the cockpit and eventually vented outside. Vacuum values vary between manufacturers (usually between 4.5 and 5.5 in Hg.(, but provide rotor speeds from 8,000 to 18,000 RPM.

5. How does the attitude indicator work? (FAA-H-8083-25)

The gyro in the attitude indicator is mounted on a horizontal plane and depends upon the rigidity in space for its operation. The horizon bar represents the true horizon. This bar is fixed to the gyro and remains in a horizontal plane as the airplane is pitched or banked about its lateral or longitudinal axis, indicating the attitude of the airplane relative to the true horizon.

6. What are the limitations of an attitude indicator? (FAA-H-8083-25)

The pitch and bank limits depend upon the make and model of the instrument. Limits in the banking plane are usually from 100 degrees to 110 degrees, and the pitch limits are usually from 60 to 70 degrees. If either limit is exceeded, the instrument will tumble or spill and will give incorrect indications until reset. A number of modern attitude indicators will not tumble.

7. What are the errors of the attitude indicator? (FAA-H-8083-15)

Attitude indicators are free from most errors, but depending upon the speed with which the erection system functions, there may be a slight nose-up indication during a rapid acceleration and a nose-down indication during a rapid deceleration. There is also a possibility of a small bank angle and pitch error after a 180° turn. These inherent errors are small and correct themselves within a minute or so after returning to straight-and-level flight.

8. How does the heading indicator operate? (FAA-H-8083-25)

The operation of the heading indicator uses the principle of rigidity in space. The rotor turns in a vertical plane, and the compass card is fixed to the rotor. Since the rotor remains rigid in space, the points on the card hold the same position in space relative to the vertical plane. As the instrument case and the airplane revolve around the vertical axis, the card provides clear and accurate heading information.

9. What are the limitations of the heading indicator? (FAA-H-8083-25)

The bank and pitch limits of the heading indicator vary with the particular design and make of instrument. On some heading indicators found in light airplanes, the limits are approximately 55 degrees of pitch and 55 degrees of bank. When either of these attitude limits is exceeded, the instrument “tumbles” or “spills” and no longer gives the correct indication until reset. After spilling, it may be reset with the caging knob. Many of the modern instruments used are designed in such a manner that they will not tumble.

10. What error is the heading indicator subject to? (FAA-H-8083-25)

Because of precession, caused chiefly by friction, the heading indicator will creep or drift from a heading to which it is set. Among other factors, the amount of drift depends largely upon the condition of the instrument. The heading indicator may indicate as much as 15° error per every hour of operation.

11. How does the turn coordinator operate? (FAA-H-8083-15)

The turn part of the instrument uses precession to indicate direction and approximate rate of turn. A gyro reacts by trying to move in reaction to the force applied thus moving the needle or miniature aircraft in proportion to the rate of turn. The slip / skid indicator is a liquid-filled tube with a ball that reacts to centrifugal force and gravity.

12. What information does the turn coordinator provide? (FAA-H-8083-25)

The turn coordinator shows the yaw and roll of the aircraft around the vertical and longitudinal axes.
The miniature airplane will indicate direction of the turn as well as rate of turn. When aligned with the turn index, it represents a standard rate of turn of 3° per second. The inclinometer of the turn coordinator indicates the coordination of aileron and rudder. The ball indicates whether the airplane is in coordinated flight or is in a slip or skid.

13. What will the turn indicator indicate when the aircraft is in a “skidding” or a “slipping” turn? (FAA-H-8083-25)

Slip – The ball in the tube will be on the inside of the turn; not enough rate of turn for the amount of bank.
Skid – The ball in the tube will be to the outside of the turn; too much rate of turn for the amount of bank.

E. Magnetic Compass

1. How does the magnetic compass work? (FAA-H-8083-25)

Magnetized needles fastened to a float assembly, around which is mounted a compass card, align themselves parallel to the earth’s lines of magnetic force. The float assembly is housed in a bowl filled with acid-free white kerosene.

2. What limitations does the magnetic compass have? (FAA-H-8083-15)

The float assembly of the compass is balanced on a pivot, which allows free rotation of the card, and allows it to tilt at an angle up to 18 degrees.

3. What are the various compass errors? (FAA-H-8083-15)

Oscillation error – Erratic movement of the compass card caused by turbulence or rough control technique.

Deviation error – Due to electrical and magnetic disturbances in the aircraft.

Variation error – Angular difference between true and magnetic north; reference isogonic lines of variation.

Dip errors :
Acceleration error – On east or west headings, while accelerating the magnetic compass shows a turn to the north, and when decelerating, it shows a turn to the south.

Remember : ANDS


Northerly turning error – The compass leads in the south half of a turn, and lags in the north of the turn.

Remember : UNOS