Bleed Air System
Air for the bleed air system can be supplied by the engines, APU, or an external air
cart/source. The APU or external cart supplies air to the bleed air duct prior to engine start.
After engine start, air for the bleed air system is normally supplied by the engines.
The following systems rely on the bleed air system for operation:
- Air conditioning/pressurization
- Wing and engine thermal anti-icing
- Engine starting
- Hydraulic reservoirs pressurization
- Water tank pressurization
- Aspirated TAT probe
Engine Bleed System Supply
Engine bleed air is obtained from the 5th and 9th stages of the compressor section. When
5th stage low pressure bleed air is insufficient for the bleed air system requirements, the
high stage valve modulates open to maintain adequate bleed air pressure. During takeoff,
climb, and most cruise conditions, low pressure bleed air from the 5th stage is adequate
and the high stage valve remains closed.
Engine Bleed Air Valves
The engine bleed air valve acts as a pressure regulator and shutoff valve. With the engine
bleed air switch ON, the valve is DC activated and pressure operated. The valve maintains
proper system operating pressure and reduces bleed air outflow in response to high bleed
air temperature.
