Definition
The temperature above which a gas cannot be liquefied by pressure alone, no matter how much pressure is applied. Each substance has its own critical temperature; below it, the gas can be compressed into a liquid, and above it, it will remain a gas regardless of pressure.
Plain English
The temperature limit beyond which squeezing a gas can no longer turn it into a liquid. If the gas is hotter than this, pressure alone won't make it liquid.
Context Anchor
Seen in discussions of gases, vapors, fuel behavior, oxygen systems, and other aircraft systems where pressure and temperature affect whether a substance is a gas or a liquid.
Derivation
From Latin 'criticus' meaning 'decisive' or 'turning point.' The word marks the temperature where a decisive change in behavior happens — above it, the rules of liquefaction no longer apply.
Why Pilots Care
Crossing this temperature without proper precautions can lead to rapid ice accumulation that reduces lift, increases drag, and may block pitot tubes or control surfaces.
Grounding Statement
Picture trying to squeeze steam back into water in a sealed cylinder. If the steam is hot enough, no amount of squeezing will turn it into water — that threshold is its critical temperature.
Intuition Check
Critical does not simply mean dangerous here. It means a specific cutoff point: below it, pressure can liquefy the gas; above it, pressure alone cannot.
Example Sentence 1
Because oxygen is stored above its critical temperature in aircraft systems, it remains a gas even under very high pressure.
Example Sentence 2
When the outside air temperature reached the critical temperature, the pilot turned on the pitot heat.