Aircraft General Knowledge
Aircraft General Knowledge covers the airframe, engine, systems, and instruments a PPL pilot must understand well enough to detect malfunctions and make safe decisions. Expect questions on the four-stroke cycle, carburettor icing, magnetos, fuel, electrical, pitot-static, and gyroscopic instruments.
Powerplant and systems
- Four-stroke cycle: intake, compression, power, exhaust. The magnetos are independent of the battery and keep the engine running if the alternator fails.
- Carburettor icing: most likely at 0–20°C with high humidity; apply carburettor heat and expect a temporary power drop.
- Fuel: check quantity, quality, and strainer; know tank selection and unusable fuel.
- Electrical: the alternator charges the battery and bus; monitor ammeter or voltmeter.
- Pitot-static: airspeed, altimeter, and VSI use pitot and static pressure; a blocked static source affects all three.
- Gyroscopic: attitude and heading indicators are usually vacuum-driven; the turn coordinator is electric.
Worked example
The altimeter is set to 1000 hPa instead of the correct QNH 1013 hPa. The aircraft is on a field 300 ft above MSL. A lower pressure setting makes the altimeter over-read by roughly 30 ft per hPa: 13 × 30 = 390 ft. It therefore indicates about 690 ft on the ground. The reasoning: the altimeter senses static pressure and converts it to altitude using the set reference; a lower reference pressure corresponds to a higher indicated altitude.
Traps
Students confuse carburettor heat with mixture, or assume a magneto check is optional. A blocked pitot tube affects airspeed but not the altimeter; a blocked static source affects all three pressure instruments. Vacuum failure leaves the attitude and heading indicators unreliable, but the turn coordinator may still work.