Air Systems (bleed, cooling, anti-ice, starting)
What this domain tests
Air Systems covers bleed extraction, cooling, anti-ice, and starting air. The exam tests bleed sources, the penalties of bleed, valve logic, and how cooling air protects the turbine.
Core rules
- Bleed air comes from LP or HP compressor stages. LP bleed is used at high power; HP bleed is used at low power and for starting.
- Bleed air supplies ECS/pressurization, wing and nacelle anti-ice, engine starting, and turbine cooling. Each use costs thrust and fuel.
- Turbine cooling air is taken from the compressor and routed through internal passages; it is not free because it bypasses the combustor.
- Anti-ice valves are controlled by aircraft or engine systems; nacelle anti-ice usually uses HP bleed. Starting bleed is time-limited.
Worked example
An engine produces 100 kN with bleeds closed. Opening a bleed that takes 5% of core flow reduces thrust by roughly the same order, say to 95 kN, and increases TSFC because the compressor still does work on the bleed air. If the bleed is used only for 10 minutes during icing conditions, the fuel penalty is finite but the thrust margin must be checked for climb. The reasoning: bleed air is compressed but does not produce thrust, so it is a direct cycle penalty.
Traps
Assuming bleed air is free; using HP bleed when LP is available; forgetting anti-ice can be automatic; confusing starting bleed with turbine cooling air; ignoring bleed effects on EGT margin.