Plain English Meaning

Something that almost certainly will not happen, but isn't completely impossible.

Full Definition

In aviation risk assessment, a likelihood category indicating that an event is very unlikely to occur during the normal operation or expected lifetime of a system, activity, or training program, though it remains theoretically possible.

Context Anchor

Used when estimating the chance of a problem during flight planning, training, or an instructor’s risk discussion.

Derivation

From Latin 'improbabilis' — 'im-' meaning 'not' and 'probabilis' meaning 'likely.' So literally 'not likely.' Knowing this helps because in risk matrices, 'improbable' is a precise tier on a scale, not a casual 'probably won't happen.'

Why Pilots Care

Misjudging an improbable event as impossible can lead to complacency, while treating it as can cause unnecessary .