Aircraft Systems: Electrical, Hydraulic, Pneumatic, Fuel, Ice and Rain Protection
What this domain tests
This domain examines system architecture and operation: electrical, hydraulic, pneumatic, fuel, and ice and rain protection. Expect questions on busbars, pressure values, valve function, and anti-ice versus de-ice.
Core rules
- Electrical: light aircraft use 28 V DC; transport aircraft use 115 V AC at 400 Hz. Busbars are arranged as main, essential, and emergency; a TRU converts AC to DC; the battery provides emergency DC.
- Hydraulic: 3,000 psi is a common transport pressure; Skydrol is a phosphate-ester fluid. An accumulator damps pulses and stores energy; a relief valve protects the system; a priority valve keeps essential consumers supplied.
- Pneumatic: engine bleed air is taken from HP or IP stages, regulated by a pressure-regulating shutoff valve, cooled in a precooler, and used for packs and anti-ice.
- Fuel: boost pumps, crossfeed, vents, unusable fuel, and jettison affect range and CG.
- Ice and rain: anti-ice prevents ice (pitot heat, windshield heat); de-ice removes it (boots, TKS weeping wing).
Worked example
A hydraulic actuator has a piston area of 2.0 in² and a rod that leaves an annulus area of 1.4 in². At 3,000 psi, extension force = 3,000 × 2.0 = 6,000 lbf; retraction force = 3,000 × 1.4 = 4,200 lbf. The actuator is stronger in extension because full piston area is pressurised.
Traps
Assuming equal force in both directions; mixing psi and bar; confusing anti-ice with de-ice; thinking 400 Hz is a DC frequency; ignoring the essential bus after a generator failure.