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PPL Aircraft General Knowledge Prep

Engines, electrics, instruments and airframes.

Pass mark 12/16 45 minutes UK CAA How many can I get wrong?
Little and often beats one big session. Five minutes on the bus counts.
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Q1. What type of fuselage construction relies on a framework of longitudinal and diagonal members, with the outer skin carrying little or no structural load?
  • A.  Truss (framework) construction
  • B.  Semi-monocoque construction
  • C.  Monocoque construction
  • D.  Geodetic construction
Show answer & explanation
✓ Answer: A. Truss (framework) construction
Truss construction uses welded steel tube or wooden frameworks to carry the loads, with fabric or thin skin simply providing an aerodynamic covering. In semi-monocoque and monocoque designs the skin itself is a primary load-bearing member, which is the key distinction examiners test for.
Q2. Most light aircraft piston engines have two independent magneto ignition systems, each firing its own spark plug in every cylinder. What is the main reason for this?
  • A.  It doubles the engine's power output
  • B.  It provides redundancy so the engine keeps running if one system fails, and improves combustion
  • C.  It allows the pilot to run the engine on half power for training
  • D.  It reduces the engine's fuel consumption by half
Show answer & explanation
✓ Answer: B. It provides redundancy so the engine keeps running if one system fails, and improves combustion
Dual magnetos give redundancy — if one fails or is switched off the other keeps the engine running, which is why the run-up check confirms both work. Firing two plugs per cylinder also gives a more complete, even burn, but it does not double power output or halve fuel burn.
Q3. What is detonation in a piston aero engine, and why is it dangerous?
  • A.  Normal, controlled burning of the fuel-air mixture that simply happens faster than usual
  • B.  Uncontrolled, explosive combustion of the remaining mixture after normal ignition, causing damaging pressure spikes
  • C.  A backfire through the induction system caused by a rich mixture at idle
  • D.  The sound made by the exhaust valve closing under high RPM
Show answer & explanation
✓ Answer: B. Uncontrolled, explosive combustion of the remaining mixture after normal ignition, causing damaging pressure spikes
Detonation is an abnormal, near-instantaneous explosion of the unburned end-gas after normal spark ignition has started the burn, producing sharp pressure spikes that can damage pistons, rings and cylinder heads. It is not the same as a controlled burn, an induction backfire, or a mechanical valve noise.
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Airframes & structures · 37
Piston engines & propellers · 35
Fuel, oil & cooling systems · 40
Electrics, ignition & avionics basics · 35
Pressure instruments & gyros · 37
The compass & instrument errors · 36
PPL Aircraft General Knowledge Prep — common questions
Frequently asked
How many questions are in the PPL Aircraft General Knowledge Prep?
The exam has 16 questions. Every Revision Robin mock uses the same 16-question format so your practice matches the real thing.
What is the pass mark for the PPL Aircraft General Knowledge Prep?
You need 12 out of 16 correct to pass, which is about 75%. Our mocks mark you against this exact threshold.
How long do you get?
The test is timed at 45 minutes. Our full mock runs on the same clock so you can practise your pacing.
Are these the real exam questions?
No. Our questions are original and written to match the current syllabus, so they give realistic practice without copying the official paper. Every answer comes with a plain-English explanation. Always confirm current rules and content with UK CAA.