Pneumatic / Vacuum

Bleed-air sources and distribution, its uses, leak detection, and vacuum systems.

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The pneumatic (bleed-air) system taps hot, high-pressure air from the engine COMPRESSOR (at more than one stage, selected by valves for the pressure needed), supplemented by the APU load compressor and a ground air cart.
Bleed air is pressure- and temperature-regulated and fed to a distribution manifold with ISOLATION valves so systems can be separated and one source can feed the whole aircraft if needed.
USES include air conditioning and pressurisation, wing/engine ANTI-ICE, engine STARTING (the air-turbine starter), hydraulic reservoir and potable-water pressurisation, and (on some) hydraulic pump drive.
A bleed-air LEAK is dangerous (hot, high-pressure air near structure/wiring) and is detected by OVERHEAT sensing loops that warn the crew to shut off the affected duct.
Older/light aircraft use engine-driven VACUUM pumps to run air-driven gyros; suction is regulated and filtered.
⚠ Exam trap: pneumatic air is tapped from the engine COMPRESSOR (bleed), and feeds air conditioning, anti-ice, engine start and pressurisation; a bleed-air LEAK is detected by OVERHEAT detection loops, not smoke detectors.

Solved examples

Name four aircraft services supplied by engine bleed (pneumatic) air.
Engine bleed air commonly supplies: (1) air conditioning and cabin pressurisation (via the packs); (2) thermal anti-icing of the wing leading edges and engine cowls; (3) engine starting through the air-turbine starter; and (4) pressurisation of the hydraulic reservoirs and the potable-water system. It may also feed cargo heating and, on some types, drive hydraulic pumps.

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