Definition
To deliberately reduce the air pressure inside a pressurized aircraft cabin so it equals the outside ambient pressure. This is done by opening outflow valves, shutting off pressurization air sources, or climbing/descending to an altitude where the pressure differential is zero.
Plain English
To let the higher-pressure air inside the cabin out, so the inside and outside pressures match.
Context Anchor
Seen in emergency procedures for pressurized airplanes, including smoke, fire, and cabin-pressure problems.
Derivation
Built from 'de-' (Latin, meaning 'remove' or 'undo') and 'pressurize' (to add pressure). So it literally means 'to undo the pressurization' — to take the added pressure back out.
Why Pilots Care
Vents smoke and combustion products rapidly while limiting oxygen available to the fire and preparing the aircraft for an emergency descent.
Intuition Check
Depressurize does not mean “turn off the air conditioning” or simply “cool the cabin.” It means reducing the actual air pressure inside the cabin.
Example Sentence 1
After confirming the cabin fire, the crew descended to 10,000 feet and depressurized the cabin to help vent the smoke.
Example Sentence 2
Depressurizing before the emergency descent prevented pressure differentials from complicating the procedure.