PPL(A) 020 Aircraft General KnowledgeRevision notes and practice questions

PPL 020 Aircraft General KnowledgeFree sample, 10 questions

1. 1A low-wing cantilever monoplane is in steady level flight. Which loads mainly act on the upper and lower skins of the wing?

   1. Upper skin in tension, lower skin in compression.
   2. Upper skin and lower skin both mainly in tension.
   3. Upper skin in compression, lower skin in tension.
   4. Upper skin and lower skin both mainly in shear.
   Show the answer

   Answer C. Lift bends the wing upwards about its root, like a beam fixed at one end. The upper surface is therefore squeezed (compression) and the lower surface stretched (tension), while the spar webs carry shear and the wing also sees some torsion from its pitching moment. The inverted answer is the classic trap: it describes the loads with the wing hanging on the ground, not in flight.

2. 2Why is a tailwheel aeroplane more prone to a ground loop than a tricycle-gear aeroplane?

   1. Its centre of gravity is ahead of the main wheels, so any swing tends to increase.
   2. Its tailwheel cannot be steered, so the aeroplane cannot be controlled on the ground.
   3. Its propeller torque is higher than that of a tricycle aeroplane of the same power.
   4. Its centre of gravity is behind the main wheels, so any swing tends to increase.
   Show the answer

   Answer D. On a tailwheel aeroplane the centre of gravity lies behind the main wheels. Once a swing starts, the inertia of the CG acts behind the pivot point and pulls the tail further round, so the swing grows into a ground loop unless the pilot corrects it at once. On a tricycle aeroplane the CG is ahead of the main wheels and a swing tends to straighten itself, which is why the inverted answer is wrong.

3. 3On a conventional elevator fitted with a trim tab, the pilot trims to relieve a steady pull force on the control column. How does the trim tab move?

   1. Up, so that the elevator moves up together with it.
   2. Down, so that the air load on the tab holds the elevator up.
   3. Up, so that the air load on the tab holds the elevator down.
   4. Down, so that the elevator moves down with it.
   Show the answer

   Answer B. A trim tab always moves opposite to the control surface it trims. To hold the elevator up without a pull force, the tab moves down: the air load on the tab pushes the elevator trailing edge up and keeps it there. Thinking that the tab moves in the same direction as the surface is the classic exam trap. The PA-28 stabilator instead carries an anti-servo tab, which moves in the same direction as the stabilator to increase the control force and is trimmed by shifting its neutral position, which is why the question specifies a conventional elevator.

4. 4During the pre-flight inspection, the pilot takes a fuel sample from a wing tank drain. A clear globule rests at the bottom of the blue fuel in the sampler. What is it and what should the pilot do?

   1. Water; keep draining until the samples show only clean blue fuel, before flight.
   2. Water; it is lighter than AVGAS and will evaporate, so the flight can proceed.
   3. Jet A-1; empty the sampler back into the tank and continue the inspection.
   4. An air bubble; it is normal after refuelling and needs no action.
   Show the answer

   Answer A. Water is heavier than AVGAS, so it sinks to the lowest points of the tanks, where the drains are fitted, and appears as a clear bead at the bottom of the sample. The pilot keeps draining until no more water appears, checking every drain, because water reaching the engine can stop it. A sample must never be poured back into the tank if it is contaminated.

5. 5In cruise, the low-voltage warning light comes on and the ammeter shows a discharge. The alternator cannot be reset. What is the best course of action?

   1. Switch off the master switch at once, otherwise the engine will stop when the battery is flat.
   2. Increase the engine RPM to raise the alternator output and continue the planned flight.
   3. Switch off non-essential electrical equipment and land as soon as practicable.
   4. Continue normally, since the battery will recharge itself once the load is reduced.
   Show the answer

   Answer C. With the alternator off line, the battery alone supplies the electrical system and will run down. Shedding non-essential loads extends the time during which the radio and other essential equipment remain available, and landing as soon as practicable avoids losing them. The engine keeps running because the magnetos are independent of the aircraft electrical system, so switching off the master switch to protect the engine is not needed.

6. 6A four-cylinder, four-stroke piston engine runs at 2400 RPM. How many power strokes per minute does the engine produce in total?

   1. 1200
   2. 2400
   3. 9600
   4. 4800
   Show the answer

   Answer D. In a four-stroke engine, each cylinder completes one cycle (induction, compression, power, exhaust) every 2 crankshaft revolutions. Each cylinder therefore gives 2400 / 2 = 1200 power strokes per minute, and four cylinders give 4 x 1200 = 4800. The 9600 answer assumes one power stroke per revolution, which applies to a two-stroke engine.

7. 7In cruise with a fixed-pitch propeller, OAT +12 °C and high humidity, the RPM slowly decreases at a constant throttle setting and the engine begins to run roughly. What is the most likely cause and the correct action?

   1. Carburettor icing; apply partial carburettor heat to limit the loss of power.
   2. Mixture too rich; lean the mixture until the RPM recovers.
   3. Carburettor icing; apply full carburettor heat and expect more roughness before the RPM rises.
   4. Detonation; enrich the mixture and reduce power.
   Show the answer

   Answer C. The cooling caused by fuel evaporation and the pressure drop in the venturi can produce carburettor ice at outside temperatures well above 0 °C, typically between about -5 and +30 °C in humid air. With a fixed-pitch propeller the first symptom is a gradual RPM drop, then rough running. Full heat is applied: the engine first runs more roughly as the melted ice passes through, then the RPM rises. Partial heat, without a carburettor air temperature gauge, can raise the air temperature into the range where icing is most severe.

8. 8In cruise with a constant-speed propeller, the pilot advances the throttle without moving the propeller lever. What happens?

   1. RPM increases, manifold pressure stays the same and the blade angle remains fixed throughout.
   2. Manifold pressure and RPM both increase, as with a fixed-pitch propeller.
   3. Manifold pressure increases, RPM stays nearly constant and the governor increases the blade angle.
   4. Manifold pressure increases, RPM stays nearly constant and the governor decreases the blade angle.
   Show the answer

   Answer C. The throttle sets manifold pressure and the propeller lever sets the RPM that the governor holds. When more power is applied, the flyweight governor coarsens the blades (larger blade angle) so that the extra power is absorbed without an RPM rise. A finer blade angle would let the RPM increase, which is the behaviour of a fixed-pitch propeller, not of a governed one.

9. 9In cruise, the oil pressure gauge shows a steady fall while the oil temperature rises above the normal range. What is the most likely cause and the correct action?

   1. A loss of oil: reduce power and plan to land as soon as possible, ready for an engine failure.
   2. Carburettor icing: apply full carburettor heat and keep the same power setting.
   3. A lean cruise mixture: enrich the mixture and continue the flight as planned.
   4. A faulty oil pressure gauge: ignore it, since the engine still runs smoothly.
   Show the answer

   Answer A. Low oil pressure together with high oil temperature confirms a real lubrication problem, typically a loss of oil, because two independent indications agree. The engine may seize, so power is reduced and the pilot lands as soon as possible with a field in mind. A gauge failure is only suspected when one indication changes alone while the other stays normal.

10. 10Climbing in cloud at 0 °C with the pitot heat off, the pilot sees the indicated airspeed rise steadily although attitude and power are unchanged. The altimeter and the VSI behave normally. What is the most likely cause?

    1. The static port is blocked: the airspeed indicator now behaves like an altimeter.
    2. The pitot tube and its drain hole are blocked: the airspeed indicator now behaves like an altimeter.
    3. The pitot tube is blocked with the drain open: trapped ram pressure makes the IAS rise.
    4. The alternate static source has opened: the airspeed indicator over-reads slightly.
    Show the answer

    Answer B. With the pitot and its drain blocked, the pressure in the pitot line is trapped while static pressure keeps falling in the climb, so the ASI over-reads more and more: it behaves like an altimeter, and under-reads in the descent. A blocked static port is excluded, since it would freeze the altimeter and set the VSI to zero. A blocked pitot with an open drain lets the trapped pressure escape, so the IAS falls towards zero instead of rising.