Definition
CAT has two distinct meanings in aviation. (1) Category: a classification grouping, used in contexts such as aircraft category (e.g., airplane, rotorcraft), instrument approach category based on aircraft approach speed, or ILS category (CAT I, II, III) defining the precision and minimums of an instrument landing system. (2) Clear-air turbulence: sudden, often severe turbulence occurring in cloudless air, most commonly at higher altitudes near the jet stream or at the boundaries between air masses moving at different speeds, with no visual cues to warn the pilot.
Plain English
CAT stands for one of two things. As 'category,' it's a way of grouping aircraft, approaches, or landing systems by their characteristics. As 'clear-air turbulence,' it's bumpy air that hits without warning in a clear sky, usually up high where fast-moving air streams meet slower air.
Context Anchor
Seen in FAA acronym lists, weather discussions, NOTAMs, and operational text where abbreviations are used to save space.
Derivation
Both meanings share the acronym but come from different roots. 'Category' comes from the Greek kategoria, meaning 'a class or division.' 'Clear-air turbulence' is plain English describing exactly what it is: turbulence in air that is clear — no clouds, no visible weather, no warning.
Why Pilots Care
It can produce sudden, unforecasted jolts that risk passenger or crew injury and require immediate speed reduction or altitude change.
Intuition Check
Do not assume CAT has only one aviation meaning. Check the sentence around it: if the text is about rules, groups, or classes, CAT likely means category; if it is about weather or ride conditions, CAT likely means clear-air turbulence.
Example Sentence 1
The approach plate listed different minimums for each CAT, so the pilot checked the aircraft's approach category before briefing.
Example Sentence 2
Passengers were asked to keep seat belts fastened because moderate CAT was reported ahead.