What are some uses of bleed air?

• A. Cabin pressurization, heating, and cooling; deicing; pneumatic starting; auxiliary drive units
• B. It is only used for starting the engine
• C. Only for cabin pressurization
• D. Only for anti-icing systems

Answer: (A)

Bleed air is high‑pressure, hot air taken from the engine compressor stages that serves as a readily available energy source for several aircraft systems. In the environmental control system it provides cabin pressurization and, after being conditioned by packs, heating and cooling for the cabin and avionics spaces. It is also used for anti-icing, routed through ducts to heat leading edges and other surfaces to prevent ice buildup. For starting each engine (and the APU in some configurations), bleed air drives an air‑turbine starter to spin the engine up. Additionally, bleed air powers auxiliary drive units, which use pneumatic energy to drive hydraulic pumps and other accessories when needed. Because it’s hot and pressurized, the bleed-air system includes valves and cooling/conditioning steps to deliver the right temperature and pressure to each user, and to shut off or isolate sources as safety requires.