Plain English Meaning

The cabin suddenly loses its pressurized air, and within seconds the inside of the aircraft matches the thin, cold air outside. The crew must put on oxygen masks right away and descend to a lower altitude where breathing is normal again.

Full Definition

The sudden loss of cabin pressure in a pressurized aircraft, occurring fast enough that cabin pressure equalizes with the lower outside pressure within seconds. It exposes occupants to high-altitude conditions — low oxygen, low temperature, and possible physical effects from the pressure change — and requires immediate use of supplemental oxygen and a to a .