Aircraft General Knowledge: Airframe, Systems and Powerplant
This domain tests how the airframe, hydraulic, pneumatic, fuel, ice-protection and powerplant systems work together, and what happens when one fails. Questions are system-logic based rather than pure memorisation.
Hydraulics and pneumatics
- Transport aircraft typically use 3,000 psi hydraulic systems, often with multiple independent circuits for redundancy.
- Engine bleed air supplies air-conditioning, pressurisation and anti-ice. Bleed valves close during engine start or fire to protect the system.
- Pressurisation is controlled by outflow valves; cabin differential pressure is limited by relief valves.
Fuel and ice protection
Fuel is fed from tanks via boost pumps; crossfeed allows an engine to run from either side. Kerosene freezes near -47°C, so fuel/oil heat exchangers warm the fuel. Wing anti-ice is usually thermal (bleed air); propeller and probe anti-ice may be electrical.
Worked example
A hydraulic actuator has a piston area of 2 in² and system pressure is 3,000 psi. Force = pressure × area = 3,000 × 2 = 6,000 lbf. If the pump delivers 10 gpm, actuator speed depends on flow divided by area, not on pressure alone. Pressure determines force; flow determines speed.
Traps that cost marks
- Assuming hydraulic pressure rises when flow increases; pressure is set by the system relief valve.
- Confusing anti-ice (prevents ice) with de-ice (removes ice).
- Forgetting that a failed bleed valve can affect pressurisation, anti-ice and engine start.