Aircraft General Knowledge (Airframe, Systems, Powerplant, Instruments)
What this paper tests
Aircraft general knowledge covers airframe, powerplant, systems and flight instruments. Questions ask why a system behaves as it does and how a failure shows up on the gauges, so learn the cause-and-effect chain rather than a list of component names.
Powerplant
- Four-stroke cycle: induction, compression, combustion, exhaust - two crankshaft revolutions per complete cycle.
- Mixture is rich for take-off and climb to cool the charge and preserve detonation margins; it is leaned in cruise to hold exhaust gas temperature within limits and avoid plug fouling.
- Carburettor ice can form with outside air temperatures from about −15 °C to +30 °C when humidity is high. Carburettor heat bypasses the air filter; applying it may briefly roughen the engine as ice melts.
- Two magnetos provide independent ignition. A drop beyond roughly 150 rpm, or a dead magneto, grounds the aircraft.
- Constant-speed propellers trade engine power (manifold pressure) against propeller load (rpm); avoid high manifold pressure with low rpm.
Airframe, systems and instruments
- The pitot-static system feeds the airspeed indicator (pitot pressure) while the altimeter and vertical speed indicator use static pressure.
- Attitude and heading indicators rely on rigidity in space; the turn coordinator relies on precession and shows rate of turn, not bank angle.
- Gyros are usually vacuum or pressure driven, with the turn coordinator electrically driven - check the vacuum gauge in the pre-flight and during climb.
Worked example
You cruise at an indicated 3000 ft with the altimeter subscale set to 1000 hPa, but the local QNH is 1013 hPa. The 13 hPa difference equals 13 × 30 ft ≈ 390 ft, so your true altitude is about 3390 ft. Flying from high to low pressure without resetting leaves you lower than indicated - 'high to low, look out below'.
Traps that cost marks
- Mixing up the four stroke names or the number of crankshaft revolutions per cycle.
- Leaving carburettor heat on in cruise, which costs power and heats induction air unnecessarily.
- Confusing magnetic compass turning error (ANDS: accelerate north, decelerate south in the northern hemisphere) with deviation.
- Forgetting that a blocked pitot with a clear static source makes the airspeed indicator behave like an altimeter.