Aircraft General Knowledge (Airframe, Systems, Electrics, Powerplant)
Aircraft General Knowledge covers airframe structure, flight controls, hydraulics, electrical generation and distribution, piston powerplants, fuel and oil systems, and the instruments that display them. The PPL exam tests the purpose of each system, its normal operation, and the failure modes a pilot must recognise in flight.
Powerplant
A four-stroke piston engine runs induction, compression, power, exhaust. Two magnetos give independent ignition; the run-up mag check should show a small, roughly equal rpm drop on each. The mixture control compensates for falling air density with altitude: lean for cruise, rich for take-off and climb.
Carburettor icing
Fuel vaporisation and the venturi pressure drop cool the charge, so ice can form at ambient temperatures up to about 38°C when humidity is high. It is most likely at low power, such as descent or glide, and shows as a gradual rpm or manifold-pressure loss. Apply full carb heat early.
Electrics
A 14 V or 28 V alternator charges the battery and supplies the bus; the battery is for starting and emergency. After an alternator failure the battery is the only source, so shed non-essential loads and land as soon as practicable.
Instruments
Pitot-static: airspeed indicator, altimeter, vertical speed indicator. Gyroscopic: attitude indicator, heading indicator, turn coordinator, driven by vacuum or electricity. A blocked static port affects all three pressure instruments; a blocked pitot affects the ASI only.
Worked example
OAT 10°C, relative humidity 60%, cruising at low power, and the rpm begins to fall. The carburettor temperature drop of roughly 20°C brings the air close to its dewpoint, so ice is the likely cause. Apply full carb heat and expect a rough engine as the ice melts.
Traps
Confusing manifold pressure with rpm; assuming carb ice needs visible moisture; forgetting that a blocked static port moves the ASI, altimeter and VSI together.