Aircraft General Knowledge - Airframe, Systems and Powerplant
Aircraft General Knowledge covers the airframe and its systems - structure, flight controls, hydraulics, electrics, pneumatics, pressurisation, fuel, ice and rain protection, fire protection, landing gear and brakes - plus the gas turbine powerplant and its limitations. The exam favours system purpose, power source, indications and the consequences of a failure rather than memorised schematics.
Airframe and structure
- Semi-monocoque stressed-skin construction: frames and stringers carry bending, the skin carries shear and tension.
- Fail-safe and safe-life design philosophies, fatigue cycles, corrosion prevention and inspection thresholds.
Systems
- Hydraulics: engine-driven pumps, electric pumps, accumulators, priority valves and system segregation so one failure cannot jam every control. Typical system pressure is around 3,000 psi.
- Electrics: AC generators, transformer-rectifier units, battery for essential DC, bus transfer and automatic shedding of non-essential loads.
- Pneumatics: engine bleed feeds the air-conditioning packs (air-cycle machine), pressurisation and airframe anti-ice.
- Pressurisation: the outflow valve schedules cabin altitude and differential pressure; maximum differential is a structural limit.
Powerplant
- A twin- or triple-spool turbofan uses N1 (LP/fan) as the primary thrust indication and N2 (HP) for starting and monitoring; EGT or ITT is the temperature limit.
- FADEC schedules fuel and start; compressor stall or surge shows as a bang, sharp EGT rise and rpm fluctuation.
Worked example
A cabin altitude of 8,000 ft corresponds to about 753 hPa; at FL350 ambient pressure is about 235 hPa. Differential pressure is 753 − 235 = 518 hPa. Since 1 psi is about 69 hPa, that is roughly 7.5 psi. If the aircraft maximum differential is 8.0 psi the cabin is within limits. If the outflow valve jammed closed during climb, differential would rise towards the structural limit, and the positive-pressure relief valve would protect the hull.
Traps
- Confusing N1 with N2, or EGT with TGT.
- Mixing psi and hPa in a differential-pressure question.
- Assuming a system failure means loss of control: know the redundancy, manual reversion and the associated checklist.