Definition
Air that has been mechanically squeezed into a smaller volume than it would naturally occupy, raising its pressure above the surrounding atmospheric pressure. In aircraft, compressed air is produced by engine-driven compressors, turbine engine bleed sources, or ground service carts, and is used to power systems such as pneumatic instruments, de-icing boots, brakes, door seals, and engine starting.
Plain English
Air that has been pushed into a smaller space so it pushes back harder. That extra push is then used to do work — like inflating boots, running tools, or starting engines.
Context Anchor
Seen in aircraft servicing, tire inflation, landing gear strut servicing, and air-powered aircraft systems.
Derivation
From Latin 'comprimere' — 'com-' meaning 'together' and 'premere' meaning 'to press.' Compressed air is literally air that has been pressed together.
Why Pilots Care
Supplies reliable power for brakes, emergency gear extension, and other systems when hydraulic power is unavailable.
Analogy
A bicycle pump is a simple example. When you push the handle down, you squeeze air into a smaller space and raise its pressure so it can fill the tire.
Grounding Statement
When you pump up a bicycle tire, the air inside is compressed — squeezed into a smaller space so it pushes outward with more force. Aircraft use that same principle on a larger scale.
Intuition Check
Compressed air is not a different kind of air. It is ordinary air being held or delivered at higher-than-normal pressure.
Example Sentence 1
Compressed air from the turbine engine's bleed system inflates the wing de-icing boots.
Example Sentence 2
During the emergency gear extension, the pilot released compressed air from the onboard bottle to lower the landing gear.