Fact & Fable

A jet keeps its cabin pressurized by supplying compressed, conditioned air and controlling how quickly air escapes. The cabin holds a higher pressure than the thin atmosphere outside, even though some air continuously leaves the aircraft. That balance lets passengers breathe at a pressure resembling a much lower altitude while the airplane cruises far above it. The important moving part is often an outflow valve: a controlled exit that helps determine how much pressure builds up inside. The need starts with the atmosphere. Air pressure falls as altitude increases, so a breath taken high above Earth contains fewer oxygen molecules than the same-sized breath near sea level. A cabin provides an enclosed environment where that pressure can be raised. This is why an airplane can travel through air that would be unsuitable for an unprotected person while its passengers sit comfortably inside. The aircraft carries a small, managed environment along with it. NASA: Air pressure at altitude . Pi...