Bleed/Pneumatic System

Question 1

What does the bleed system do, and what systems is it connected to?

Answer 1

Provides hot pressurised air for anti-ice, air conditioning, water pressure, hydraulic reservoirs, and engine starting.

Question 2

What are the various bleed air sources?

Answer 2

1. Engine intermediate compressor stage
2. Engine high pressure compressor stage (when press/temp of IP too low eg. low engine rpm 36 +/-4)
3. APU bleed. Has priority but cannot be used for anti-ice.

Question 3

What happens after air is tapped from the engine bleed system?

Answer 3

BMC (Bleed Monitoring Computer) will tap air from IP/HP automatically.
Bleed air passes through engine bleed valve, and overpressure valve to pre-cooler.
Air cooled to around 200C then fed to various bleed demands.

Question 4

Describe APU bleed system.

Answer 4

APU bleed has priority over engine bleed, when APU BLEED pb pushed.
When APU BLEED pb pushed, APU BLEED valve opens, XFEED valve opens, and ENG BLEED valves close.
APU bleed air avail when rotor speed >90% and supplied on ENG 1 side of sys.

Question 5

How is bleed sys affected following loss of an engine?

Answer 5

Engine Flameout - XBLEED valve can be opened and both packs run. If WAI required, turn one PACK OFF.

Engine Failure with damage/fire - XBLEED valve closed to prevent contamination. WAI unavailable. QRH app spd increment for structural icing.

Above MLW with engine damage - If GA perf affected, flap 3 for approximately, ENG BLEEDs OFF. (AC can be run from APU BLEED but only if ENG 1 running).

Question 6

Where is the Eng A/Ice bleed air tapped from?

Answer 6

From the eng bleed pre-cooler. Spring loaded NRV prevents air re-entering pre-cooler.