Aircraft General Knowledge (Airframe, Systems, Powerplant, Electrics)
What the exam tests
Airframe, systems, powerplant and electrics questions test how an aircraft generates and distributes power, how subsystems fail, and which indications follow.
Core systems
- Electrical: 115 V AC 400 Hz from IDGs, 28 V DC from transformer-rectifiers, battery for essential DC; bus ties let one generator supply both sides.
- Hydraulics: engine-driven pumps, electric backups, a power transfer unit, ram air turbine for total loss.
- Pneumatics: bleed air from IP/HP compressor stages, precooled, used for packs, anti-ice and starting.
- Fuel: Jet A-1, feed tanks, crossfeed, unusable fuel, jettison where fitted; APU supplies ground bleed and electric power.
- Pressurization uses an outflow valve; cabin differential is limited by the pressure hull.
Worked example
If generator 1 trips, the bus tie closes and generator 2 picks up bus 1. If both main generators are lost, the APU generator or battery/essential bus takes over; on many types the RAT deploys automatically. Flight controls, standby instruments and one VHF normally remain on the essential bus.
Traps
Mixing up a TRU (AC to DC) with an inverter (DC to AC); assuming the battery supplies all AC loads; forgetting that bleed air for anti-ice reduces engine thrust; and treating IDG disconnect as identical to generator failure.