Plain English Meaning

Being tired enough that your thinking, reactions, and judgment are not as sharp as they should be — even if you don't fully realize it.

Full Definition

A state of reduced mental and physical performance caused by inadequate rest, prolonged exertion, stress, or disrupted sleep patterns. In aviation, fatigue degrades alertness, reaction time, judgment, and decision-making, and is recognized by the FAA as a significant risk factor in flight safety. It is the 'F' in the IMSAFE personal-readiness checklist pilots use to self-assess fitness for flight.

Context Anchor

Seen in the IMSAFE self-check before flight, especially when considering sleep, long duty days, , stress, or repeated training flights.