Bleed Air

Bleed air is high-pressure, high-temperature air extracted (or "bled") from the compressor section of a jet engine. This compressed air is routed through a network of ducts and valves to power several critical aircraft systems.

Primary uses of bleed air include:

• Cabin pressurization and air conditioning: Bleed air is cooled through air cycle machines and mixed with recirculated cabin air
• Engine starting: Bleed air from one engine (or the APU) is used to spin up and start other engines
• Anti-ice protection: Hot bleed air is routed to wing leading edges, engine inlets, and other surfaces prone to ice accumulation
• Hydraulic reservoir pressurization
• Water system pressurization

Notable exception: The Boeing 787 Dreamliner uses a bleedless architecture, replacing most bleed air functions with electrically powered systems for improved fuel efficiency.