Aircraft General Knowledge
Aircraft General Knowledge
This domain examines the piston-engine light aircraft a PPL candidate typically flies: airframe, flight controls, powerplant, fuel, electrical, pitot-static and gyroscopic instruments. You need to understand what each system does, how it fails, and what indications follow.
Core concepts
- Four-stroke cycle: induction, compression, combustion, exhaust. The mixture control adjusts fuel/air ratio; leaning is needed at high density altitude.
- Dual magnetos provide independent ignition. A mag check at run-up detects fouling or a dead magneto; excessive drop needs investigation.
- Carburettor icing can occur at outside air temperatures well above freezing, especially in humid or descending conditions. Carb heat first, then adjust mixture.
- Constant-speed propellers: manifold pressure and RPM are separate controls; avoid excessive manifold pressure at low RPM.
- Pitot-static errors: blocked pitot affects airspeed; blocked static affects altimeter, VSI and airspeed. Know the alternate static source.
- Electrical failure: alternator/generator loss leaves battery power for essential radios and instruments; shed load and land as soon as practicable.
Worked example
During descent, the engine runs rough and the RPM drops. The pilot applies carburettor heat, the roughness worsens briefly, then improves. Reason: ice in the carburettor is melting; the initial roughness is expected. The pilot should leave carb heat on, richen mixture if needed, and monitor RPM. Applying mixture lean first would mask the cause and could raise combustion temperature.
Traps that cost marks
Using carb heat only when the outside air temperature is near freezing; mistaking a mag drop for carb icing; assuming a gauge is correct after a static blockage; and forgetting that an alternator failure may not stop the engine but will deplete the battery.