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

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Question 1Aircraft General Knowledge

In a four-stroke reciprocating engine, during which stroke is the intake valve normally open and the piston moving toward bottom dead centre?

  1. Intake stroke Correct answer.
  2. Compression stroke
  3. Exhaust stroke
  4. Power stroke

Explanation

The intake stroke draws the fuel-air mixture into the cylinder. The piston travels from top dead centre toward bottom dead centre while the intake valve is open, creating a pressure drop that admits the charge.

Question 2Aircraft General Knowledge

What is the primary function of the magneto in a piston aero engine?

  1. To convert alternating current from the alternator into direct current
  2. To regulate the fuel-air mixture entering the cylinders
  3. To step down battery voltage for the starter motor
  4. To supply a high-tension voltage for the spark plugs independently of the aircraft electrical system Correct answer.

Explanation

A magneto is a self-contained generator that produces high voltage for ignition using rotating magnets and a coil. Because it needs no external power source, ignition continues even if the aircraft electrical system fails.

Question 3Aircraft General Knowledge

Why is dual ignition, with two spark plugs per cylinder, used in aircraft piston engines?

  1. It removes the need for a carburettor heat control
  2. It allows the engine to run on two different fuel grades simultaneously
  3. It provides redundancy and shortens the flame travel time, improving combustion efficiency Correct answer.
  4. It enables the propeller to reverse pitch during braking

Explanation

Two spark plugs create two flame fronts that burn the charge more rapidly and completely, which improves power and economy. The second independent magneto system also provides redundancy if one ignition circuit fails.

Question 4Aircraft General Knowledge

Which component converts the reciprocating motion of the pistons into rotational motion of the crankshaft?

  1. The camshaft
  2. The valve lifter
  3. The accessory drive gear
  4. The connecting rod Correct answer.

Explanation

The connecting rod links the piston to the crankshaft journal. As the piston moves up and down, the rod transmits the force to the offset crank throw, producing rotation of the crankshaft.

Question 5Aircraft General Knowledge

What does the octane or performance number of an aviation gasoline indicate?

  1. Its tendency to absorb water from the atmosphere
  2. Its resistance to detonation under high temperature and pressure Correct answer.
  3. Its freezing point at altitude
  4. Its lubricating quality for the valve guides

Explanation

The grade of avgas, such as 100 or 100LL, expresses its anti-knock quality. A higher performance number means the fuel can withstand greater compression and temperature before detonating.

Question 6Aircraft General Knowledge

In a simple float-type carburettor, what is the purpose of the venturi?

  1. To maintain a constant fuel level in the float chamber
  2. To filter contaminants from the incoming fuel
  3. To accelerate the airflow and create a low-pressure region that draws fuel from the discharge nozzle Correct answer.
  4. To prevent fuel from flowing when the engine is inverted

Explanation

As air passes through the narrowed throat of the venturi its velocity increases and its static pressure falls. This pressure difference between the float chamber and the venturi draws fuel out through the main discharge nozzle.

Question 7Aircraft General Knowledge

What is the primary purpose of the oil in a piston aero engine?

  1. To increase the compression ratio of the engine
  2. To reduce friction, assist cooling and carry contaminants to the filter Correct answer.
  3. To raise the octane rating of the fuel
  4. To provide the spark energy for combustion

Explanation

Oil forms a lubricating film between moving surfaces, absorbs heat from hot components and transports it to the cooler, and carries wear particles to the filter. It also helps seal the piston rings.

Question 8Aircraft General Knowledge

On a constant-speed propeller, what does the propeller governor do?

  1. It meters oil to the propeller hub to hold a selected RPM as load or airspeed changes Correct answer.
  2. It controls the position of the cowl flaps
  3. It limits the maximum manifold pressure available at full throttle
  4. It sets the mixture strength for the selected power setting

Explanation

The governor senses engine RPM and adjusts oil pressure to the propeller hub, changing blade angle so that the selected RPM is maintained. This lets the propeller absorb power efficiently across a range of airspeeds and power settings.

Question 9Aircraft General Knowledge

An engine oil temperature gauge suddenly reads high while oil pressure remains normal. Which condition is most consistent with these indications?

  1. An empty oil tank
  2. A failed oil pressure relief valve
  3. A partially blocked oil cooler or restricted cooling airflow Correct answer.
  4. A broken oil pump drive shaft

Explanation

High oil temperature with normal pressure suggests the oil is being heated faster than the cooler can reject heat. A blocked cooler matrix or restricted airflow over it fits this pattern. Loss of oil or pump failure would instead produce a pressure drop.

Question 10Aircraft General Knowledge

During a descent with the throttle closed, the carburettor air temperature gauge shows a fall toward the yellow arc. What is the appropriate pilot action?

  1. Reduce RPM by selecting a coarser propeller pitch
  2. Lean the mixture to raise combustion temperature
  3. Apply carburettor heat and expect the gauge reading to rise Correct answer.
  4. Increase throttle to wide open to warm the induction air

Explanation

Carburettor heat supplies warmer induction air, so the carburettor air temperature indication should rise. Use heat in accordance with the aircraft's AFM/POH. A temporary RPM or power reduction may occur, particularly as ice clears, but this should not be confused with a falling carburettor air temperature indication.

Question 11Aircraft General Knowledge

An engine is running rough and the pilot performs a magneto check. Selecting the left magneto produces no change in RPM, while selecting the right magneto causes a large drop. What is the most likely explanation?

  1. The right magneto is producing excessive spark advance
  2. The mixture is too lean at high altitude
  3. The propeller governor is slipping
  4. The left magneto circuit is not firing, so the engine was running on the right magneto alone Correct answer.

Explanation

When a magneto is switched off, RPM should drop as the engine runs on one plug per cylinder. No drop when selecting left indicates the left magneto was already not contributing, so the engine was running on the right magneto. This must be investigated before flight because no ignition redundancy remains.

Question 12Aircraft General Knowledge

What is the effect of opening the throttle on manifold pressure in a normally aspirated engine at a constant altitude?

  1. Manifold pressure rises toward ambient pressure Correct answer.
  2. Manifold pressure rises above ambient pressure
  3. Manifold pressure falls toward zero
  4. Manifold pressure remains unchanged

Explanation

With the throttle closed, manifold pressure is well below ambient because the pistons draw against a restriction. Opening the throttle reduces that restriction, so manifold pressure rises and approaches, but cannot exceed, ambient pressure at that altitude.

Question 13Aircraft General Knowledge

Why does detonation damage an aircraft piston engine?

  1. The fuel ignites before the spark, causing a loss of power only
  2. The mixture becomes too rich and fouls the spark plugs
  3. The charge burns explosively after normal ignition, producing extreme pressure peaks and high temperatures Correct answer.
  4. The spark plug fires too early, advancing the timing beyond specification

Explanation

Detonation occurs when part of the charge auto-ignites after normal combustion has begun, creating shock waves and very high peak pressures. Sustained detonation can overheat and erode pistons, rings and valves.

Question 14Aircraft General Knowledge

A pilot notices that cylinder head temperature is rising while oil temperature remains normal during a climb. Which action best addresses this?

  1. Enrich the mixture and increase airspeed or open cowl flaps to improve cooling Correct answer.
  2. Reduce airspeed to decrease ram air drag
  3. Close the cowl flaps to retain cooling air
  4. Lean the mixture further to reduce fuel consumption

Explanation

Rising cylinder head temperature with normal oil temperature suggests the cylinders are not being cooled adequately. Enriching the mixture adds fuel cooling and opening cowl flaps or increasing airspeed improves airflow through the fins.

Question 15Aircraft General Knowledge

What is the function of the exhaust gas temperature gauge in mixture management?

  1. It shows the cylinder head temperature directly
  2. It measures the temperature of the oil leaving the cooler
  3. It indicates the mixture strength by showing the temperature peak as mixture is leaned Correct answer.
  4. It indicates the manifold pressure at the throttle plate

Explanation

As the mixture is leaned from rich, exhaust gas temperature rises to a peak near stoichiometric mixture and then falls as the mixture becomes leaner. The gauge therefore lets the pilot identify the peak and set the mixture to a chosen value relative to it.

Question 16Aircraft General Knowledge

Why must the fuel selector be positioned to a tank with adequate fuel before take-off rather than relying on both tanks being selected?

  1. Both positions are only permitted during descent
  2. Many light aircraft fuel selectors have no both position, and an empty selected tank causes fuel starvation Correct answer.
  3. A single tank selection prevents vapour lock in the lines
  4. Selecting both tanks doubles the fuel pressure to the carburettor

Explanation

In many light aircraft the selector offers left, right and off, so the engine draws only from the selected tank. If that tank runs dry the engine stops even though the other tank is full, so the pilot must manage selection and quantity deliberately.

Question 17Aircraft General Knowledge

What is the purpose of the pressure relief valve in a dry-sump engine oil system?

  1. To limit maximum oil pressure by bypassing excess oil back to the sump or pump inlet Correct answer.
  2. To cool the oil before it reaches the bearings
  3. To filter metal particles from the oil
  4. To maintain a minimum oil pressure at idle

Explanation

The relief valve opens when oil pressure exceeds a set value, often when the oil is cold and viscous, and bypasses excess oil. This protects seals, hoses and the oil cooler from over-pressure.

Question 18Aircraft General Knowledge

During a run-up magneto check, the RPM drop on one magneto exceeds the manufacturer's limit and the engine runs rough. What is the most appropriate interpretation?

  1. The drop is normal and the check may be disregarded
  2. A fault exists in the ignition system and the aircraft should not be flown until it is rectified Correct answer.
  3. The propeller is out of balance and needs tracking
  4. The mixture is too rich and should be leaned for take-off

Explanation

An excessive drop or rough running on one magneto indicates a fault such as a fouled plug, faulty harness or weak magneto. Because ignition redundancy and performance are affected, the defect must be corrected before flight.

Question 19Aircraft General Knowledge

How does a turbocharger increase the power output of a piston engine at altitude?

  1. It compresses induction air using exhaust-driven turbine energy, restoring manifold pressure as ambient pressure falls Correct answer.
  2. It cools the fuel before it enters the carburettor
  3. It reduces the propeller load at high altitude
  4. It increases the compression ratio by altering the piston stroke

Explanation

An exhaust-driven turbine spins a compressor that raises the pressure of the induction air. This maintains manifold pressure and therefore power as altitude reduces ambient pressure, up to the system's critical altitude.

Question 20Aircraft General Knowledge

An engine with a fixed-pitch propeller is at full throttle and the mixture is leaned for cruise. What happens to engine RPM if the mixture is leaned beyond the best power setting?

  1. RPM decreases as power falls with the weakening mixture Correct answer.
  2. RPM increases because less fuel allows faster burning
  3. RPM rises then falls to zero immediately
  4. RPM stays constant regardless of mixture

Explanation

Leaning beyond best power reduces the energy released per cycle, so brake power and therefore RPM fall. This is why leaning in cruise is normally done to a target exhaust gas temperature rather than arbitrarily.

Question 21Aircraft General Knowledge

A pilot applies carburettor heat during cruise and observes a rise in manifold pressure with rough running that then smooths out. What does this sequence most likely indicate?

  1. The oil pressure relief valve has stuck open
  2. Carburettor ice was present and is being melted and ingested Correct answer.
  3. The magneto switch was selected to the off position
  4. The mixture control was accidentally moved to idle cut-off

Explanation

Applying heat bypasses warm air around the venturi, which initially reduces power and may cause roughness as melted ice passes through the engine. Recovery of smooth running and restored power indicates the ice has cleared.

Question 22Aircraft General Knowledge

Why is pre-ignition more dangerous than detonation when it persists?

  1. The charge ignites before the spark, so peak pressure occurs while the piston is still rising, causing severe overheating and possible mechanical failure Correct answer.
  2. It only occurs at low power settings and is self-limiting
  3. It has no effect on engine components because the spark still occurs
  4. It reduces cylinder head temperature by burning the charge earlier

Explanation

Pre-ignition occurs when a hot spot such as a glowing plug or carbon deposit ignites the charge before the spark. The early pressure rise opposes the rising piston, rapidly raising temperatures and loads and potentially causing burnt valves or holes in pistons.

Question 23Aircraft General Knowledge

An aircraft with a constant-speed propeller is climbing at a fixed throttle setting and the pilot increases propeller RPM. What is the immediate effect on engine load and manifold pressure?

  1. Blade angle decreases, engine load decreases and manifold pressure tends to rise Correct answer.
  2. Blade angle decreases and manifold pressure remains exactly constant
  3. Blade angle increases, engine load increases and manifold pressure tends to fall
  4. Blade angle increases and RPM falls further

Explanation

Selecting a higher RPM causes the governor to reduce blade angle so the propeller absorbs less torque per revolution. With the throttle unchanged, the reduced load allows the engine to accelerate and manifold pressure to rise slightly.

Question 24Aircraft General Knowledge

During a descent, a pilot reduces throttle and the manifold pressure gauge reads below the idle range while the engine runs roughly. What is the most likely cause?

  1. The throttle is closed so far that the engine is being driven by the propeller with insufficient charge, and the mixture should be adjusted or throttle opened slightly Correct answer.
  2. The magnetos have both failed simultaneously
  3. The oil pump has failed
  4. The fuel tanks are both empty

Explanation

At very low throttle settings the descending propeller drives the engine while the induction charge is small, producing rough running. Slight throttle opening or appropriate mixture adjustment restores smooth operation.

Question 25Aircraft General Knowledge

A turbocharged engine is operated above its critical altitude with the throttle fully open. What limits further increases in manifold pressure?

  1. The propeller governor increases blade angle to limit RPM
  2. The wastegate is fully closed and the turbocharger reaches its maximum compressor output for the conditions Correct answer.
  3. The mixture control automatically leans to reduce power
  4. The throttle plate is partially closed by the automatic controller

Explanation

At and above critical altitude the wastegate is fully closed and the turbocharger is producing its maximum available boost. Manifold pressure can no longer be maintained and falls as altitude increases further.

Question 26Aircraft General Knowledge

In a piston aero engine ignition system, what is the function of the magneto's breaker points?

  1. They interrupt the primary current at the correct moment to collapse the magnetic field and induce a high voltage in the secondary winding Correct answer.
  2. They advance and retard the ignition timing automatically as manifold pressure changes
  3. They rectify the alternating secondary current so the spark plugs receive direct current
  4. They regulate the voltage supplied to the spark plugs to a constant value across the RPM range

Explanation

The magneto generates its own electricity, so the primary circuit must be interrupted at the correct instant for the collapsing field to induce a high voltage in the secondary winding. The breaker points perform that switching function, and their opening moment sets ignition timing.

Question 27Aircraft General Knowledge

Which statement best describes the purpose of the engine air filter or induction air screen on a piston aircraft?

  1. It removes dust and foreign matter from induction air while allowing an alternate heated or unfiltered source if the filter blocks Correct answer.
  2. It cools the induction air to increase its density before it reaches the carburettor
  3. It meters the quantity of air entering the engine in proportion to throttle movement
  4. It prevents fuel vapour from escaping the induction system during shutdown

Explanation

The induction filter protects the engine from abrasive dust and debris; a blocked filter is bypassed through an alternate air door so the engine can keep running. Air metering is done by the throttle and fuel metering unit, not the filter.

Question 28Aircraft General Knowledge

What is the primary function of the engine cowling and its baffles on an air-cooled horizontally opposed engine?

  1. To increase the compression ratio by containing crankcase pressure
  2. To support the engine mount and carry flight loads into the firewall
  3. To store a reserve of cooling oil around the cylinder barrels
  4. To direct cooling air around the cylinders and fins in a controlled path and to reduce aerodynamic drag Correct answer.

Explanation

The cowling smooths airflow over the engine for drag reduction, while internal baffles force cooling air to flow through the cylinder fins rather than around them. Without baffling, much of the cooling air would bypass the hot surfaces.

Question 29Aircraft General Knowledge

In a light aircraft fuel system, what does the fuel strainer or gascolator primarily do?

  1. It pressurises the fuel line to the carburettor
  2. It collects water and sediment at a low point where they can be drained during the pre-flight check Correct answer.
  3. It measures fuel flow so the pilot can lean the mixture
  4. It prevents fuel from flowing back to the tank after shutdown

Explanation

The gascolator is placed at the lowest point of the fuel system so water and sediment settle where a drain valve can remove them before flight. It is a filter-and-settling device, not a pump or measuring instrument.

Question 30Aircraft General Knowledge

What is the purpose of the propeller reduction gearbox on many light aircraft engines?

  1. It allows the engine to turn faster than the propeller so the engine can develop useful power while the propeller stays within efficient tip speeds Correct answer.
  2. It allows the propeller to freewheel when the engine stops in flight
  3. It increases propeller RPM above engine RPM to improve take-off thrust
  4. It converts the reciprocating motion of the pistons into rotation of the crankshaft

Explanation

Direct-drive engines turn the propeller at engine speed, but geared engines let the crankshaft spin faster than the propeller. This keeps propeller tip speed below the range where compressibility losses and noise become severe while letting the engine operate at a power-producing RPM.

Question 31Aircraft General Knowledge

What does the red line on an engine tachometer represent?

  1. The minimum RPM for sustained cruise flight
  2. The maximum continuous or maximum permissible engine RPM established by the manufacturer Correct answer.
  3. The RPM at which the magneto check must be performed
  4. The RPM above which the propeller governor begins to feather the blades

Explanation

The red radial line on the tachometer marks the maximum RPM limit the engine may be operated at, and exceeding it risks overstress and overheating. It is a limitation, not a check or cruise reference.

Question 32Aircraft General Knowledge

What is the function of the aircraft battery in a typical light aircraft electrical system?

  1. It regulates the charging voltage supplied to the electrical bus
  2. It supplies high voltage directly to the magnetos for spark generation
  3. It converts alternating current from the alternator into direct current for the avionics
  4. It stores electrical energy to start the engine and provides a reserve supply when generator or alternator output is insufficient Correct answer.

Explanation

The battery provides the cranking current for starting and acts as a buffer or emergency source when the alternator cannot meet the load. Charging voltage regulation and rectification are performed by other components.

Question 33Aircraft General Knowledge

What is the purpose of the master switch in a light aircraft?

  1. It arms the engine fire extinguishing system
  2. It selects which magneto is active for engine start
  3. It opens the fuel shut-off valve before engine start
  4. It connects or disconnects the battery and alternator from the main electrical bus Correct answer.

Explanation

The master switch controls the main battery and alternator contactors, connecting the electrical bus to its power sources. It is the central control for electrical power distribution, separate from ignition and fuel controls.

Question 34Aircraft General Knowledge

A pilot notices that the fuel pressure gauge reads low while the engine-driven pump is selected, but normal when the electric boost pump is switched on. What is the most likely interpretation?

  1. The engine-driven fuel pump has failed or is delivering reduced pressure, and the boost pump is masking the fault Correct answer.
  2. The fuel selector is on the wrong tank and the boost pump is drawing from the correct tank
  3. The carburettor is running too rich and is drawing pressure from the line
  4. The fuel pressure gauge is reading incorrectly and should be ignored

Explanation

The boost pump supplying normal pressure confirms the gauge and line are serviceable, so the difference points to the engine-driven pump as the failed element. The boost pump is not a fix for a failed engine pump and the fault must be investigated.

Question 35Aircraft General Knowledge

During a climb in a normally aspirated engine, the pilot holds full throttle and the mixture at the take-off setting. What change in fuel-air ratio should be expected as altitude increases?

  1. The mixture becomes progressively leaner because fuel flow falls with altitude
  2. The mixture becomes richer because the fuel is warmed by the engine and expands
  3. The mixture remains constant because the carburettor compensates automatically for altitude
  4. The mixture becomes progressively richer because air density falls while fuel flow remains roughly constant Correct answer.

Explanation

A simple float carburettor meters fuel roughly in proportion to volume flow, while the mass of air entering falls as density decreases with altitude. The result is an increasingly rich mixture unless the pilot leans, which is why mixture leaning is required during climb and cruise.

Question 36Aircraft General Knowledge

An engine is started and the oil pressure gauge shows no indication within the manufacturer's specified time. What is the most appropriate action?

  1. Continue at low RPM until the oil warms and pressure builds
  2. Continue normally because the gauge may be slow to respond in cold weather
  3. Increase RPM to speed up oil pump priming
  4. Shut down the engine and investigate the oil system before further running Correct answer.

Explanation

A prolonged absence of oil pressure indicates a possible failure of the pump, a blocked line, or a gauge fault, and continued running can destroy the engine. The engine should be shut down promptly and the cause found before restart.

Question 37Aircraft General Knowledge

What is the effect of selecting carburettor heat during cruise on the mixture and power of a normally aspirated engine?

  1. The mixture becomes richer but power increases because fuel vaporisation improves
  2. The warmer, less dense air enriches the mixture and reduces power, so leaning may be needed Correct answer.
  3. The mixture is unaffected but manifold pressure rises
  4. The warmer air leans the mixture and increases power

Explanation

Heated induction air is less dense, so less air mass enters the engine for the same fuel flow, enriching the mixture. Power falls because the charge mass is smaller, and the pilot may need to lean after applying heat.

Question 38Aircraft General Knowledge

A pilot observes that cylinder head temperature is normal in cruise but rises sharply during a prolonged climb. Which combination of factors best explains this?

  1. The oil cooler door closes automatically during climb, raising cylinder temperature
  2. The magnetos advance timing during climb, which cools the cylinders
  3. Reduced cooling airflow at low climb speed and high power output increase heat rejection to the cylinders Correct answer.
  4. The mixture automatically leans as altitude increases, reducing combustion temperature

Explanation

During a climb the engine produces high power while airspeed and therefore cooling airflow are lower, so less heat is carried away from the cylinder fins. The combination of high heat input and reduced cooling raises CHT, which is why climb airspeed and mixture management matter.

Question 39Aircraft General Knowledge

What is the significance of the critical altitude for a turbocharged piston engine?

  1. It is the altitude at which the wastegate is fully closed at idle
  2. It is the highest altitude at which the turbocharger can maintain the selected manifold pressure with the throttle fully open Correct answer.
  3. It is the altitude above which the engine must be shut down
  4. It is the altitude at which the turbocharger first begins to rotate

Explanation

Up to the critical altitude the turbocharger can hold the desired manifold pressure; above it, the turbocharger reaches its limit and manifold pressure falls with further climb. This limit is fundamental to turbocharged engine operation and performance planning.

Question 40Aircraft General Knowledge

An engine with a constant-speed propeller is set at a fixed throttle and the pilot selects a higher propeller RPM. What happens to manifold pressure and engine load?

  1. Manifold pressure decreases because the turbocharger wastegate opens
  2. Manifold pressure tends to decrease because the engine turns faster and pumps more air, while engine friction and pumping losses increase Correct answer.
  3. Manifold pressure remains unchanged because the throttle has not moved
  4. Manifold pressure increases because the propeller loads the engine more heavily

Explanation

Increasing propeller RPM lets the engine turn faster at the same throttle opening, so it consumes more air and manifold pressure drops. The higher rotational speed also increases friction and pumping losses, which is why RPM and manifold pressure are managed together.

Question 41Aircraft General Knowledge

What is the purpose of the engine primer in a light aircraft piston engine?

  1. It injects fuel continuously to supplement the carburettor in cruise
  2. It increases fuel pressure to the carburettor during take-off
  3. It removes air from the fuel lines after maintenance
  4. It delivers a small quantity of fuel directly to the cylinders or induction system to aid starting in cold conditions Correct answer.

Explanation

The primer provides extra fuel for starting, especially when the engine is cold and fuel vaporisation is poor. It is used only for starting and is not a continuous fuel delivery device.

Question 42Aircraft General Knowledge

What does a sudden drop in oil pressure accompanied by a rise in oil temperature most likely indicate?

  1. A faulty tachometer reading
  2. A loss of oil quantity or a failure in the oil system that is reducing lubrication and cooling Correct answer.
  3. A rich mixture that is diluting the oil
  4. Normal behaviour as the engine warms up

Explanation

Oil pressure and temperature normally move in opposite directions only within limits; a simultaneous pressure drop and temperature rise suggests the oil supply is being lost. This combination warrants immediate investigation and likely shutdown.

Question 43Aircraft General Knowledge

Why is the mixture leaned before take-off at a high-elevation airport?

  1. Leaning reduces the octane requirement of the fuel
  2. Leaning lowers cylinder head temperature by reducing power output
  3. The reduced air density at altitude enriches the mixture, so leaning restores the correct fuel-air ratio and prevents rough running and fouling Correct answer.
  4. Leaning increases fuel flow to compensate for cold temperatures

Explanation

At high elevation the air is less dense, so a carburettor set for sea level delivers too much fuel for the air available. Leaning restores the proper ratio, improving smoothness and reducing plug fouling and loss of power.

Question 44Aircraft General Knowledge

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

  1. It converts the alternator's alternating output to direct current
  2. It limits the current drawn by the starter motor
  3. It controls the alternator field current so charging voltage stays within limits and the battery is not overcharged Correct answer.
  4. It disconnects the battery from the bus during engine start

Explanation

The voltage regulator modulates field current to keep system voltage at the designed value, protecting the battery and avionics. Rectification is handled by the alternator's diodes, not the regulator.

Question 45Aircraft General Knowledge

An engine is equipped with a fixed-pitch propeller and the pilot notices that static RPM at full throttle is below the manufacturer's minimum. Which factor is most likely responsible?

  1. The oil temperature is too low for full power
  2. The propeller is too small in diameter for the engine
  3. The magneto switch is selected to BOTH, which reduces RPM
  4. The engine is not developing rated power, possibly because of ignition timing, mixture, or a partially blocked induction system Correct answer.

Explanation

Static RPM is a check on whether the engine develops expected power with the propeller fitted. A low reading points to an engine problem such as timing, mixture, or induction restriction rather than to the propeller, since the propeller is the fixed reference.

Question 46Aircraft General Knowledge

What is the purpose of the wastegate in a turbocharged piston engine installation?

  1. It releases excess fuel pressure back to the tank
  2. It vents crankcase pressure to the atmosphere
  3. It regulates exhaust gas flow through the turbine to control boost pressure Correct answer.
  4. It opens the intercooler to cooling air

Explanation

The wastegate bypasses exhaust around the turbine, controlling how fast the turbocharger spins and therefore the manifold pressure produced. It is the primary boost control element in the exhaust path.

Question 47Aircraft General Knowledge

During a run-up, the engine is at 1,700 RPM and the pilot selects carburettor heat. The RPM rises slightly and then settles. What does this indicate?

  1. The mixture was slightly lean and carburettor heat enriched it toward a better setting, which is acceptable within limits Correct answer.
  2. The engine is too rich and heat is leaning it
  3. The carburettor heat valve is stuck closed
  4. The magnetos are failing

Explanation

Carburettor heat enriches the mixture because warmed air is less dense. A small RPM rise means the engine was slightly lean before heat was applied, and the enrichment moved it toward a better mixture, which is normal.

Question 48Aircraft General Knowledge

A pilot is cruising at high altitude with the mixture leaned for best economy. The engine begins to run rough. What is the most likely cause and the appropriate response?

  1. The mixture has become too lean for the conditions, so enrich it slightly until smooth operation returns Correct answer.
  2. The magnetos have failed, so select the other magneto
  3. The propeller is overspeeding, so reduce RPM
  4. The mixture is too rich, so lean it further

Explanation

Leaning to the roughness point means the mixture has passed the lean limit, and roughness is the first sign of lean misfire. Enriching slightly restores smooth combustion and protects the engine from excessive temperatures.

Question 49Aircraft General Knowledge

An engine with a constant-speed propeller is descending with the throttle retarded and the propeller control at high RPM. The manifold pressure gauge reads near the low end of its range and the engine is being driven by the propeller. What is the concern?

  1. The engine may be windmilling at high RPM with low manifold pressure, causing excessive cooling and possible shock cooling, so RPM should be reduced Correct answer.
  2. The mixture will become too rich and flood the engine
  3. The turbocharger will overspeed because exhaust flow is high
  4. The engine will overheat because the throttle is closed

Explanation

In a descent with a closed throttle and high RPM selection, the propeller drives the engine and airflow through it is high while combustion heat is low. This can cool the cylinders rapidly, so the pilot reduces RPM and manages the descent to avoid shock cooling.

Question 50Aircraft General Knowledge

A turbocharged engine is operated at high altitude with the throttle fully open and the mixture set for best power. The pilot notices that manifold pressure cannot be increased further even though the throttle is fully open. What does this indicate?

  1. The wastegate is stuck fully closed and is overboosting the engine
  2. The engine is operating at or above its critical altitude, where the turbocharger can no longer maintain the selected manifold pressure Correct answer.
  3. The mixture is too lean and is limiting power
  4. The propeller is limiting engine RPM and therefore manifold pressure

Explanation

At critical altitude the turbocharger reaches the limit of its ability to compress ambient air to the selected manifold pressure. Above that altitude, further throttle opening cannot raise manifold pressure and performance decreases with height.