Aircraft General Knowledge (Airframe, Systems, Powerplant, Electrics)
Aircraft General Knowledge checks whether you understand the machine well enough to detect abnormalities before they become emergencies: airframe structure, flight controls, piston powerplant, fuel, oil, electrics, pitot-static and vacuum systems.
Powerplant and systems
- A four-stroke piston engine produces power on the power stroke; mixture control affects fuel/air ratio, and an excessively lean mixture raises exhaust gas temperature and can damage valves.
- Carburettor icing can occur at outside air temperatures well above freezing; apply carburettor heat as the POH directs and expect an initial rpm drop.
- Magnetos are independent ignition sources; the magneto check confirms both operate and that the engine runs acceptably on each.
- Fuel grade and quantity are airworthiness items; avgas mass is about 0.72 kg per litre, so volume and mass are not interchangeable.
Electrics and instruments
- The battery starts the engine and powers essential loads; the alternator/generator carries the normal electrical load and recharges the battery.
- An ammeter or loadmeter shows whether the electrical system is charging or discharging; know which loads to shed.
- The pitot-static system feeds the airspeed indicator, altimeter and vertical speed indicator; blockage symptoms differ by port.
- The vacuum system typically drives gyroscopic instruments; suction gauge readings outside the POH range mean partial-panel planning.
Worked example
After take-off the ammeter shows a continuous discharge and the alternator warning light is on. The battery is supplying the electrical load. Reduce non-essential electrical load, avoid unnecessary radio transmission, land at the nearest suitable aerodrome and investigate. Do not assume the battery will last for the planned flight.
Traps that cost marks
- Confusing carburettor icing with airframe icing.
- Treating a magneto drop as normal without comparing it with the POH limit.
- Mixing up pitot blockage (airspeed behaves like an altimeter) with static blockage (airspeed over-reads in climb).
- Forgetting that the POH, not memory, gives the limiting values.