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NCAA PPL Aircraft General Knowledge study materials
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NCAA PPL Aircraft General Knowledge practice questions

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Question 1Aircraft General Knowledge (airframe, systems, powerplant, instruments)

In a typical light training aircraft, what is the primary function of the empennage?

  1. It absorbs landing loads transmitted through the tricycle gear
  2. It stores fuel to adjust the center of gravity
  3. It provides lift for the aircraft during slow flight
  4. It provides stability and control about the pitch and yaw axes Correct answer.

Explanation

The empennage comprises the horizontal stabilizer with elevator and the vertical stabilizer with rudder. These surfaces stabilize the aircraft and allow control about the pitch and yaw axes, complementing the ailerons that control roll.

Question 2Aircraft General Knowledge (airframe, systems, powerplant, instruments)

Which statement best describes the function of wing dihedral in a light aircraft?

  1. It increases the rate of climb at a given power setting
  2. It produces a stabilizing roll moment when the aircraft is disturbed in sideslip Correct answer.
  3. It allows the wing to carry a higher fuel load
  4. It reduces the stalling speed by increasing wing area

Explanation

With dihedral, the lower wing in a sideslip presents a greater effective angle of attack and produces more lift. This creates a rolling moment that tends to level the wings, giving lateral stability.

Question 3Aircraft General Knowledge (airframe, systems, powerplant, instruments)

What is the purpose of the fuel selector valve in a light aircraft fuel system?

  1. It regulates fuel pressure delivered to the carburetor
  2. It meters the fuel-air mixture entering the cylinders
  3. It allows the pilot to choose which tank supplies the engine Correct answer.
  4. It filters contaminants from the fuel before it reaches the engine

Explanation

The fuel selector valve directs fuel from a chosen tank to the engine, allowing the pilot to manage fuel balance and use. It is separate from pressure regulation, mixture metering, and filtration, each handled by other components.

Question 4Aircraft General Knowledge (airframe, systems, powerplant, instruments)

During a normal preflight, the pilot drains fuel from the sumps primarily to check for which condition?

  1. Improper fuel tank venting
  2. Excessive fuel pump pressure
  3. Water and sediment contamination Correct answer.
  4. Incorrect fuel octane rating

Explanation

Fuel sump drains are located at low points in the system where water and sediment collect. Sampling the fuel and inspecting it in a clear cup reveals contamination before it can reach the engine.

Question 5Aircraft General Knowledge (airframe, systems, powerplant, instruments)

In a four-stroke reciprocating engine, what occurs during the compression stroke?

  1. The intake valve opens and the fuel-air mixture enters the cylinder
  2. The exhaust valve opens and burned gases leave the cylinder
  3. The piston moves toward top dead center, reducing the volume of the trapped mixture Correct answer.
  4. The spark plug fires to ignite the mixture

Explanation

During compression, both valves are closed and the piston travels upward, reducing cylinder volume and raising the pressure and temperature of the trapped fuel-air charge. Ignition follows at the end of this stroke.

Question 6Aircraft General Knowledge (airframe, systems, powerplant, instruments)

What is the primary purpose of engine oil in an aircraft reciprocating engine?

  1. It pressurizes the fuel tanks for fuel delivery
  2. It lubricates, cools, and helps seal internal engine components Correct answer.
  3. It provides the spark needed for combustion
  4. It increases the octane rating of the fuel

Explanation

Oil forms a film between moving parts to reduce friction and wear, carries heat away from hot components, and helps seal the piston rings. It also suspends contaminants for removal by the filter.

Question 7Aircraft General Knowledge (airframe, systems, powerplant, instruments)

What is the function of the magnetos in a reciprocating engine ignition system?

  1. They charge the aircraft battery during flight
  2. They regulate the voltage supplied to the avionics
  3. They measure engine speed for the tachometer
  4. They generate high-voltage pulses that fire the spark plugs Correct answer.

Explanation

Magnetos are self-contained engine-driven generators that produce high voltage timed to the engine's rotation. This voltage is distributed to the spark plugs to ignite the fuel-air mixture independently of the aircraft electrical system.

Question 8Aircraft General Knowledge (airframe, systems, powerplant, instruments)

On a standard day at sea level, what does an altimeter set to 29.92 inHg indicate when the aircraft is on the ground at an airport with a field elevation of 1,200 feet?

  1. A value that cannot be determined without the current temperature
  2. Zero feet
  3. Approximately 1,200 feet minus the standard pressure correction
  4. 1,200 feet Correct answer.

Explanation

An altimeter indicates pressure altitude when set to 29.92 inHg, which is the altitude corresponding to the standard atmosphere. On a standard sea-level day, the airport's actual elevation equals its pressure altitude, so the altimeter reads about 1,200 feet.

Question 9Aircraft General Knowledge (airframe, systems, powerplant, instruments)

A pilot notices the ammeter shows a discharge after the alternator fails in flight. Which action best conserves electrical power?

  1. Turn off nonessential electrical equipment and land as soon as practical Correct answer.
  2. Select the battery master to off while continuing the flight
  3. Reset the alternator field breaker repeatedly until output returns
  4. Increase engine RPM to maximum to restore alternator output

Explanation

When the alternator fails, the battery is the only source of electrical power and will drain over time. Shedding nonessential loads extends battery life for essential equipment and navigation, and the pilot should plan to land before power is exhausted.

Question 10Aircraft General Knowledge (airframe, systems, powerplant, instruments)

During run-up, the pilot selects the left magneto and observes no drop in RPM. What is the most likely interpretation?

  1. The left magneto circuit may be grounding improperly, so the magneto may not be shutting off Correct answer.
  2. The engine is operating at too low an RPM for a valid check
  3. The spark plugs on the left magneto are worn and should be replaced
  4. The left magneto is functioning normally and the right is faulty

Explanation

Selecting a magneto grounds the other one so that the engine runs on the selected magneto alone, producing a normal RPM drop. If no drop occurs when the left is selected, the right magneto may not be grounding, meaning the engine continues running on both magnetos.

Question 11Aircraft General Knowledge (airframe, systems, powerplant, instruments)

An aircraft with a fixed-pitch propeller is in level flight at a constant altitude, and the pilot reduces power. What happens to the angle of attack of the propeller blades if airspeed remains constant?

  1. The angle of attack becomes negative and the propeller drives the engine
  2. The angle of attack increases because the blade's rotational velocity decreases Correct answer.
  3. The angle of attack decreases because the forward velocity increases
  4. The angle of attack remains unchanged because blade angle is fixed

Explanation

The blade angle is fixed on a fixed-pitch propeller, but the angle of attack depends on the vector sum of rotational and forward velocities. Reducing power lowers rotational velocity, so the resultant relative wind angle changes and the blade's angle of attack increases.

Question 12Aircraft General Knowledge (airframe, systems, powerplant, instruments)

What is indicated by the green arc on a typical airspeed indicator?

  1. The normal operating speed range Correct answer.
  2. The stall speed range with landing gear and flaps extended
  3. The never-exceed speed range
  4. The flap operating speed range

Explanation

The green arc spans from the stall speed in the clean configuration to the maximum structural cruising speed. This is the normal operating range in smooth air, while the yellow arc indicates caution in turbulence.

Question 13Aircraft General Knowledge (airframe, systems, powerplant, instruments)

What is the purpose of the vacuum system in a light aircraft equipped with vacuum-driven gyroscopic instruments?

  1. It pressurizes the cabin for high-altitude flight
  2. It supplies air to the engine intake at high altitude
  3. It inflates the deicing boots on the wing leading edges
  4. It provides suction to spin the gyros in the attitude and heading indicators Correct answer.

Explanation

Vacuum-driven gyros require a stream of air to spin their rotors at high speed, providing rigidity in space. The vacuum system, driven by an engine-mounted pump, supplies this airflow to the attitude and heading indicators.

Question 14Aircraft General Knowledge (airframe, systems, powerplant, instruments)

During a turn, the attitude indicator of a vacuum-driven gyroscopic system may show a slight error. What is the primary cause of this error?

  1. Electrical interference from the alternator
  2. Loss of vacuum pressure during the turn
  3. Precession of the gyro caused by the forces of the turn Correct answer.
  4. Static port blockage during the turn

Explanation

Gyroscopic instruments are subject to precession, in which applied forces cause the spin axis to move. In a turn, acceleration forces can cause the attitude indicator to indicate slightly incorrectly until the turn is stabilized.

Question 15Aircraft General Knowledge (airframe, systems, powerplant, instruments)

What is the function of the voltage regulator in an aircraft charging system?

  1. It protects the battery from overcharging by limiting current only
  2. It controls the engine RPM during cruise
  3. It limits the alternator output voltage to a safe value Correct answer.
  4. It converts alternating current to direct current

Explanation

The voltage regulator controls the field current to the alternator so that output voltage remains within a safe range. This protects the battery and electrical equipment from overvoltage while maintaining adequate charging.

Question 16Aircraft General Knowledge (airframe, systems, powerplant, instruments)

A pilot observes that the oil temperature is rising steadily while oil pressure is falling during cruise. What is the most appropriate interpretation?

  1. The oil cooler is operating too efficiently
  2. This is normal behavior as the engine warms up
  3. The oil level may be low or the oil pump may be failing, warranting a precautionary landing Correct answer.
  4. The oil pressure gauge is likely indicating incorrectly because pressure and temperature are unrelated

Explanation

Rising temperature combined with falling pressure can indicate insufficient oil, a failing pump, or a blockage in the lubrication system. Because lubrication is critical to engine life, the pilot should reduce power and land as soon as practical.

Question 17Aircraft General Knowledge (airframe, systems, powerplant, instruments)

How does carburetor ice most commonly form in a reciprocating engine?

  1. Moisture in the air freezes as it passes through the venturi, where pressure and temperature drop Correct answer.
  2. Ice forms in the fuel tanks when the outside air temperature is below freezing
  3. Ice forms on the spark plugs when the engine is shut down in cold weather
  4. Ice accumulates in the oil cooler when the engine is operated at low power

Explanation

As air accelerates through the carburetor venturi, its pressure and temperature drop, and fuel vaporization further cools the mixture. Moisture in the air can then freeze on the throttle plate and venturi walls, even at outside temperatures well above freezing.

Question 18Aircraft General Knowledge (airframe, systems, powerplant, instruments)

During a descent with the carburetor heat applied, the pilot may notice a slight power loss. What is the reason for this?

  1. The fuel flow is shut off by the carburetor heat control
  2. The heated air is less dense, so the mixture becomes richer and power decreases Correct answer.
  3. The magnetos are disabled when carburetor heat is applied
  4. The carburetor heat valve closes the throttle plate

Explanation

Carburetor heat directs warmed air from around the exhaust into the induction system. Warmer air is less dense, reducing the mass of air entering the engine and enriching the mixture, which produces a slight power loss.

Question 19Aircraft General Knowledge (airframe, systems, powerplant, instruments)

What is the primary purpose of the exhaust system in a reciprocating engine aircraft?

  1. It reduces the noise of the engine to acceptable levels only
  2. It provides structural support for the engine mount
  3. It carries burned gases away from the engine and, in some designs, provides cabin heat and turbocharging Correct answer.
  4. It supplies cooled air to the carburetor

Explanation

The exhaust system routes combustion gases safely overboard away from the engine and cabin. In many aircraft, exhaust heat is also used for cabin heating and carburetor heat, and exhaust energy can drive a turbocharger.

Question 20Aircraft General Knowledge (airframe, systems, powerplant, instruments)

A pilot flying a normally aspirated engine at high altitude notices a gradual loss of power and a rough-running engine. Which action is most appropriate?

  1. Lean the mixture to restore the proper fuel-air ratio Correct answer.
  2. Increase carburetor heat to full and leave it there
  3. Reduce RPM to idle to clear the engine
  4. Enrich the mixture to cool the engine

Explanation

At high altitude the air is less dense, so the mixture becomes overly rich unless leaned. Leaning restores the proper fuel-air ratio, improving power and smoothness and reducing spark plug fouling.

Question 21Aircraft General Knowledge (airframe, systems, powerplant, instruments)

What is the significance of the maximum structural cruising speed (Vno) on the airspeed indicator?

  1. It is the speed above which flaps may not be extended
  2. It is the speed above which flight should be conducted only in smooth air Correct answer.
  3. It is the speed at which the landing gear should be retracted
  4. It is the speed at which the aircraft should be rotated for takeoff

Explanation

Vno marks the upper limit of the green arc, above which the aircraft should be flown only in smooth air to avoid structural loads from turbulence. Flight in the yellow arc between Vno and Vne requires caution.

Question 22Aircraft General Knowledge (airframe, systems, powerplant, instruments)

Why are fuel tanks in many light aircraft vented to the atmosphere?

  1. To pressurize the tank and force fuel to the engine
  2. To allow air to enter and replace fuel as it is consumed, preventing a vacuum Correct answer.
  3. To provide a source of air for the cabin
  4. To allow fuel vapor to escape and increase the octane rating

Explanation

As fuel is drawn from a tank, air must enter to replace the volume; otherwise a partial vacuum would form and could stop fuel flow. Vent lines also allow the tanks to equalize pressure during climbs and descents.

Question 23Aircraft General Knowledge (airframe, systems, powerplant, instruments)

A pilot notices that the turn coordinator shows a standard rate turn but the ball is displaced to the outside of the turn. What does this indicate?

  1. The aircraft is in coordinated flight and no action is needed
  2. The turn coordinator is inoperative and should be disregarded
  3. The aircraft is in a skidding turn and the bank should be increased
  4. The aircraft is in a slipping turn and rudder pressure should be adjusted Correct answer.

Explanation

The ball in the inclinometer indicates the coordination of the turn. If the ball is displaced to the outside, the aircraft is slipping, and the pilot should apply rudder toward the ball to coordinate the turn.

Question 24Aircraft General Knowledge (airframe, systems, powerplant, instruments)

Why is it important to avoid abrupt throttle movements in an aircraft equipped with a constant-speed propeller?

  1. Abrupt changes cause the magnetos to lose timing
  2. Abrupt changes increase the voltage output of the alternator
  3. Abrupt changes can cause the propeller governor to overspeed or the engine to overboost Correct answer.
  4. Abrupt changes cause the fuel tanks to vent excessively

Explanation

A constant-speed propeller governor adjusts blade pitch to maintain a selected RPM. Abrupt throttle changes can momentarily cause the propeller to overspeed or the engine to overboost, so smooth power changes protect the engine and propeller.

Question 25Aircraft General Knowledge (airframe, systems, powerplant, instruments)

During a climb in an aircraft with a turbocharged engine, the pilot observes that manifold pressure remains constant as altitude increases. What does this indicate about the turbocharger operation?

  1. The turbocharger has failed and the wastegate is fully open
  2. The engine is operating at maximum continuous power without limitation
  3. The mixture is too lean and the engine is detonating
  4. The turbocharger is maintaining sea-level manifold pressure by compressing intake air Correct answer.

Explanation

A turbocharger compresses intake air to maintain manifold pressure as altitude increases and air density decreases. Constant manifold pressure in the climb indicates the turbocharger is functioning as designed, subject to its altitude and temperature limits.

Question 26Aircraft General Knowledge (airframe, systems, powerplant, instruments)

Which structural component of a semi-monocoque fuselage carries the primary bending and shear loads along its length?

  1. The bulkheads only
  2. The stringers and longerons Correct answer.
  3. The outer skin alone
  4. The fabric covering

Explanation

In semi-monocoque construction the skin carries part of the load, but the longitudinal stringers and longerons provide the stiffness and strength needed to resist bending and shear along the fuselage. Bulkheads and frames hold the shape and transfer concentrated loads rather than carrying the main longitudinal loads.

Question 27Aircraft General Knowledge (airframe, systems, powerplant, instruments)

What is the function of a wing spar in a light aircraft wing?

  1. It controls the position of the aileron trim tab
  2. It acts as the main longitudinal beam that carries lift-induced bending loads Correct answer.
  3. It houses the fuel tank vent lines
  4. It provides the airfoil's camber shape at the trailing edge

Explanation

The spar is the principal structural beam of the wing, running spanwise and carrying the bending moments generated by lift. Ribs attach to the spar to form the airfoil shape, and skin attached to the structure carries torsional and shear loads.

Question 28Aircraft General Knowledge (airframe, systems, powerplant, instruments)

Which control surface produces the yawing motion used to keep a turn coordinated?

  1. The elevator
  2. The ailerons
  3. The rudder Correct answer.
  4. The flaps

Explanation

The rudder is hinged to the vertical stabilizer and deflects airflow sideways, generating a horizontal force about the vertical axis that yaws the aircraft. Yaw control is used to counteract adverse yaw and to coordinate turns with the ailerons.

Question 29Aircraft General Knowledge (airframe, systems, powerplant, instruments)

In a hydraulically actuated landing gear system, what is the purpose of the selector valve?

  1. It filters contaminants from the hydraulic fluid
  2. It stores hydraulic fluid under pressure for emergency use
  3. It limits the maximum system pressure
  4. It directs hydraulic pressure to extend or retract the gear Correct answer.

Explanation

The selector valve is operated by the pilot and routes pressurized fluid to the appropriate side of the actuating cylinders to raise or lower the gear. A check valve, relief valve, and filter perform separate functions within the same system.

Question 30Aircraft General Knowledge (airframe, systems, powerplant, instruments)

What is the purpose of the shimmy damper on a nosewheel assembly?

  1. It absorbs vertical landing loads
  2. It locks the nosewheel straight for takeoff
  3. It dampens rapid side-to-side oscillation of the nosewheel Correct answer.
  4. It provides nosewheel steering input

Explanation

A shimmy damper uses hydraulic resistance to suppress the rapid oscillatory motion of the nosewheel that can occur at certain speeds on the ground. It does not steer the wheel, lock it, or carry vertical loads, which are handled by the strut and steering linkages.

Question 31Aircraft General Knowledge (airframe, systems, powerplant, instruments)

What does the yellow arc on a typical airspeed indicator represent?

  1. The caution range, to be entered only in smooth air Correct answer.
  2. The normal operating range
  3. The flap operating range
  4. The never-exceed speed

Explanation

The yellow arc marks the caution range between maximum structural cruising speed and never-exceed speed, where the aircraft should be flown only in smooth air. The green arc is the normal range, the white arc is the flap range, and the red line is Vne.

Question 32Aircraft General Knowledge (airframe, systems, powerplant, instruments)

What does the white arc on an airspeed indicator define?

  1. The caution range
  2. The flap operating range Correct answer.
  3. The normal operating range
  4. The never-exceed speed

Explanation

The white arc spans from the stall speed in the landing configuration to the maximum speed at which flaps may be extended. It tells the pilot the safe speed band for flap operations during approach and landing.

Question 33Aircraft General Knowledge (airframe, systems, powerplant, instruments)

Which instrument in a light aircraft directly displays the rate of climb or descent in feet per minute?

  1. The altimeter
  2. The attitude indicator
  3. The vertical speed indicator Correct answer.
  4. The airspeed indicator

Explanation

The vertical speed indicator senses the rate of change of static pressure and displays it as a climb or descent rate in feet per minute. It lags briefly during changes because of the calibrated leak in its case.

Question 34Aircraft General Knowledge (airframe, systems, powerplant, instruments)

What causes the lag in a vertical speed indicator immediately after a climb or descent begins?

  1. Gyroscopic precession of the internal rotor
  2. Expansion of the static line due to temperature
  3. The calibrated leak between the case and the instrument diaphragm Correct answer.
  4. Friction in the pitot tube

Explanation

The VSI compares pressure inside a diaphragm with case pressure through a calibrated leak, and that leak takes a few seconds to equalize, producing the familiar lag. This is why the needle stabilizes after a short delay when the rate of climb changes.

Question 35Aircraft General Knowledge (airframe, systems, powerplant, instruments)

Which instrument uses a gyroscope that depends on rigidity in space rather than on the Earth's rotation?

  1. The magnetic compass
  2. The vertical speed indicator
  3. The altimeter
  4. The attitude indicator Correct answer.

Explanation

The attitude indicator uses a gyroscope whose rotor stays fixed in space, so the instrument case moves around it to show pitch and bank. The magnetic compass and the pitot-static instruments do not rely on gyroscopic rigidity.

Question 36Aircraft General Knowledge (airframe, systems, powerplant, instruments)

What is the primary purpose of the engine primer in a light aircraft with a reciprocating engine?

  1. It delivers a small quantity of fuel directly to the cylinders for starting Correct answer.
  2. It increases fuel pressure to the carburetor during cruise
  3. It purges vapor from the fuel lines in flight
  4. It enriches the mixture automatically at high altitude

Explanation

The primer pump injects fuel directly into the intake ports or cylinders to provide the rich mixture needed for a cold start. It is operated only briefly before start and is not used to manage mixture or fuel pressure in normal operation.

Question 37Aircraft General Knowledge (airframe, systems, powerplant, instruments)

What is the purpose of the carburetor heat system in a light aircraft?

  1. It warms the fuel before it enters the float bowl
  2. It heats the intake air to improve cruise fuel economy
  3. It supplies heated air to the carburetor to melt or prevent ice Correct answer.
  4. It prevents vapor lock in the fuel lines

Explanation

Carburetor heat routes air that has been warmed by the exhaust or a heat muff into the carburetor, raising the temperature enough to melt existing ice or prevent its formation. A side effect is a slightly richer mixture and reduced power because the heated air is less dense.

Question 38Aircraft General Knowledge (airframe, systems, powerplant, instruments)

A pilot notices the fuel pressure gauge fluctuating rapidly during climb with the electric boost pump off. What is the most likely cause?

  1. The fuel quantity gauge is reading incorrectly
  2. The engine-driven fuel pump is drawing air or vapor Correct answer.
  3. The oil pressure relief valve is stuck open
  4. The magneto timing is too advanced

Explanation

Rapid fuel pressure fluctuations with the boost pump off often indicate the engine-driven pump is intermittently picking up air or vapor, which can lead to power loss. Selecting the boost pump on and checking for a loose fuel line or low tank level is the appropriate response.

Question 39Aircraft General Knowledge (airframe, systems, powerplant, instruments)

What is the function of the propeller governor in a constant-speed propeller system?

  1. It regulates oil pressure to the propeller hub to maintain the selected RPM Correct answer.
  2. It controls the engine throttle valve position
  3. It sets the ignition timing advance
  4. It adjusts the fuel mixture at altitude

Explanation

The governor senses engine RPM and meters oil pressure to the propeller hub, changing blade angle to hold the RPM selected by the pilot. When RPM rises, the governor increases oil pressure to increase blade angle and load the engine.

Question 40Aircraft General Knowledge (airframe, systems, powerplant, instruments)

Why does a constant-speed propeller allow the engine to operate at a selected RPM independent of airspeed changes?

  1. The propeller diameter changes with airspeed
  2. The blade angle automatically changes to absorb the available power Correct answer.
  3. The ignition timing advances with RPM
  4. The throttle valve is adjusted by the governor

Explanation

As airspeed or power changes, the governor changes blade angle so the propeller absorbs the engine's power at the selected RPM. This keeps the engine in an efficient operating range and reduces pilot workload.

Question 41Aircraft General Knowledge (airframe, systems, powerplant, instruments)

What is the primary function of the alternator in a light aircraft electrical system?

  1. It converts alternating current to direct current for the battery
  2. It generates electrical power to run the electrical loads and charge the battery Correct answer.
  3. It provides the high voltage for the spark plugs
  4. It regulates the voltage supplied to the bus

Explanation

The alternator is driven by the engine and produces electrical power for the aircraft's loads while charging the battery. The rectifier converts its AC output to DC, and the voltage regulator controls the output level.

Question 42Aircraft General Knowledge (airframe, systems, powerplant, instruments)

What happens to the electrical system if the alternator fails in flight while the battery remains connected?

  1. The magnetos stop producing spark immediately
  2. The engine stops because the fuel pump loses power
  3. The electrical loads continue at full power indefinitely
  4. The battery supplies the electrical loads until it is depleted Correct answer.

Explanation

With the alternator offline, the battery becomes the only source of electrical power and will discharge as it supplies the loads. The engine continues to run because magnetos are independent of the electrical system.

Question 43Aircraft General Knowledge (airframe, systems, powerplant, instruments)

What is the purpose of the vacuum pump in an aircraft with vacuum-driven gyroscopic instruments?

  1. It provides suction to the fuel system
  2. It draws air through the instrument gyros to spin them Correct answer.
  3. It pressurizes the cabin for high-altitude flight
  4. It cools the avionics during flight

Explanation

The vacuum pump creates suction that draws air through the gyro instrument cases, spinning the rotors that provide rigidity in space. A vacuum gauge lets the pilot monitor the system pressure.

Question 44Aircraft General Knowledge (airframe, systems, powerplant, instruments)

What does a high reading on the vacuum gauge indicate in a light aircraft with vacuum-driven gyros?

  1. A normal condition during climb
  2. Insufficient suction and unreliable gyro indications
  3. Excessive suction that may damage the gyro instruments Correct answer.
  4. A failure of the engine-driven fuel pump

Explanation

The vacuum gauge indicates the suction level; too little suction makes the gyros unreliable, while excessive suction can cause wear or damage to the instruments. The pilot should check the gauge against the manufacturer's normal range.

Question 45Aircraft General Knowledge (airframe, systems, powerplant, instruments)

What is the function of the exhaust gas temperature gauge in a reciprocating engine aircraft?

  1. It measures the oil temperature
  2. It indicates the cylinder head temperature
  3. It helps the pilot set the fuel mixture for efficient operation Correct answer.
  4. It shows the manifold pressure

Explanation

The EGT gauge shows the temperature of the exhaust gases, and the pilot uses it to lean the mixture by reference to peak EGT. It is a mixture-management tool rather than a direct measure of cylinder head temperature.

Question 46Aircraft General Knowledge (airframe, systems, powerplant, instruments)

What is indicated by the manifold pressure gauge in a normally aspirated engine when the throttle is fully closed during a descent?

  1. The same reading as the oil pressure
  2. A pressure below ambient atmospheric pressure Correct answer.
  3. A pressure above ambient atmospheric pressure
  4. Zero pressure at all altitudes

Explanation

With the throttle closed, the engine acts as a pump and the intake pressure falls below ambient, so the manifold pressure gauge reads less than the surrounding atmospheric pressure. The gauge is calibrated so that ambient pressure is the upper limit for a normally aspirated engine.

Question 47Aircraft General Knowledge (airframe, systems, powerplant, instruments)

What is the purpose of the cylinder head temperature gauge in an air-cooled engine?

  1. It indicates the exhaust gas mixture setting
  2. It shows the oil pressure in the engine
  3. It measures the temperature of the induction air
  4. It warns of excessive cylinder temperatures that could damage the engine Correct answer.

Explanation

The CHT gauge monitors the temperature of the cylinder heads, which is critical in air-cooled engines where cooling depends on airflow. Excessive CHT can lead to detonation or cylinder damage, so the pilot reduces power or enriches the mixture if it rises too high.

Question 48Aircraft General Knowledge (airframe, systems, powerplant, instruments)

What is the effect of detonation on an aircraft engine if it continues unchecked?

  1. It improves engine efficiency at high power settings
  2. It has no effect on engine temperatures
  3. It can cause rapid overheating and mechanical damage to the engine Correct answer.
  4. It only affects the exhaust system

Explanation

Detonation is uncontrolled, explosive combustion that raises cylinder pressures and temperatures sharply, potentially damaging pistons, valves, and bearings. The pilot should reduce power, enrich the mixture, and increase airspeed to improve cooling.

Question 49Aircraft General Knowledge (airframe, systems, powerplant, instruments)

What is the purpose of the oil cooler in an aircraft reciprocating engine installation?

  1. It increases oil pressure at high altitude
  2. It stores oil for the engine during inverted flight
  3. It regulates oil temperature by transferring heat to the airflow Correct answer.
  4. It filters contaminants from the oil

Explanation

The oil cooler is a heat exchanger that dissipates heat from the oil into the air stream to keep oil temperature within limits. In some installations a vernatherm valve bypasses the cooler when the oil is cold.

Question 50Aircraft General Knowledge (airframe, systems, powerplant, instruments)

Why does an aircraft with a fixed-pitch propeller typically use a mixture control that must be leaned as altitude increases?

  1. The throttle valve closes as altitude increases
  2. Fuel pressure increases with altitude, so the mixture becomes leaner
  3. Air density decreases with altitude, so less fuel is needed for the same air mass Correct answer.
  4. The carburetor automatically enriches the mixture at altitude

Explanation

As altitude rises, air density falls, so the carburetor delivers less air mass for a given throttle setting while the fuel flow remains relatively fixed. Leaning the mixture restores the correct fuel-to-air ratio, improving efficiency and reducing fouling.