Plain English Meaning

A quiet kind of impairment where the pilot is still awake and seems okay, but is actually not thinking or reacting well enough to fly safely. The danger is that they often don't realize anything is wrong.

Full Definition

A partial or gradual reduction in a pilot's physical or mental performance during flight, where the pilot remains conscious and apparently functional but is no longer capable of performing flight duties safely. Unlike obvious incapacitation, the pilot may not recognize the impairment and may continue to attempt to fly the aircraft, often with degraded judgment, slower reactions, or impaired decision-making.

Context Anchor

Seen in aeromedical and instrument flying discussions, especially when judging whether a pilot is fit to fly or when unexplained mistakes start appearing in flight.