Definition
High-pressure, high-temperature air tapped from one of the compressor stages of a gas turbine engine and routed through ducts to perform work elsewhere on the aircraft. Common uses include cabin pressurization, air conditioning, engine and wing anti-icing, engine starting, and pneumatic system operation.
Plain English
Hot, pressurized air taken from inside a jet engine's compressor and piped to other parts of the aircraft to do useful jobs like pressurizing the cabin, heating leading edges to prevent ice, or starting another engine.
Context Anchor
Seen in turbine aircraft systems, especially when discussing pressurization, heating, anti-ice systems, engine starts, and bleed air warnings.
Derivation
Bleed' here means to draw off or tap a small amount from a larger flow, the same sense used when bleeding brakes or bleeding a radiator. The compressor is generating far more pressurized air than the engine needs for combustion, so a portion is bled off for other uses.
Why Pilots Care
Proper management of bleed air affects engine efficiency, thrust, and the operation of critical systems; overuse can reduce performance.
Grounding Statement
Picture a turbine engine as a powerful air pump: compressor bleed air is some of that pumped-up air being sent to the airplane instead of continuing through the engine.
Intuition Check
Bleed does not mean the air is leaking by accident here. It means air is intentionally tapped from the engine, unless the context specifically says there is a bleed air leak.
Example Sentence 1
After the bleed air valve failed closed, the crew lost cabin pressurization and had to descend to a lower altitude.
Example Sentence 2
Excessive use of compressor bleed air can lead to reduced engine thrust during takeoff.