Aircraft General Knowledge - Structures, Systems, Powerplant and Instrument Logic
The NCAA CPL Aircraft General Knowledge paper tests whether you can explain how structure, systems and powerplant interact - and predict what the instruments and warnings show when a component fails. Expect system-reasoning items rather than pure definitions.
Airframe and flight controls
- Semi-monocoque construction: the skin carries most of the load, stiffened by stringers and frames. Fail-safe design provides alternate load paths and crack stoppers, while safe-life items (landing gear, some rotating parts) are retired at a fixed life.
- Primary controls are ailerons, elevator and rudder; flaps, trim and spoilers are secondary. Cable circuits rely on turnbuckles, fairleads and pulleys - free play or lost motion is a rigging and flutter concern.
Systems
- Hydraulics: engine-driven pump plus electric backup, an accumulator (absorbs surges and holds pressure for emergency gear or brakes), relief valve, selector valves and actuators; transport types typically run near 3,000 psi.
- Electrical: battery for starting and emergency supply, alternator or generator with a voltage regulator, bus ties, an essential bus and circuit breakers.
- Fuel: boost pumps, tank vents, sump drains for water, and unusable fuel that is never planned as range.
- Ice and rain: pitot heat, pneumatic boots or TKS fluid, and windshield heat.
Powerplant
Reciprocating engines run the four-stroke cycle; magnetos are independent of the battery, and carburettor ice is most likely between about 0 °C and 20 °C with high humidity. Turbines are described by N1 (LP/fan), N2 (HP) and EGT, and the fuel control schedules fuel against those parameters.
Worked example
The pitot tube blocks while the static source stays clear, and the aircraft climbs at constant indicated speed. The ASI will read increasing, behaving like an altimeter. Trapped pitot pressure stays fixed while ambient static pressure falls with height, so the differential across the capsule grows. In a descent the ASI under-reads. If the static source also blocks, the ASI freezes, the altimeter freezes and the VSI reads zero.
Traps
Mixing N1 and N2; assuming the battery can carry normal load after alternator failure; counting unusable fuel; forgetting that a blocked static port corrupts all three pitot-static instruments at once.