Plain English Meaning
One of the airplane's engines has stopped working, and the airplane is flying on the engine or engines that are still running.
Full Definition
A flight condition in a multi-engine airplane in which one engine has failed or has been intentionally shut down, while the remaining engine or engines continue to produce power. Many multi-engine performance figures and V-speeds (such as VMC, VYSE, and VXSE) are defined specifically for this condition.
Context Anchor
Seen in multiengine training, emergency procedures, and V-speed discussions about how the airplane performs and handles after one engine stops helping.
Derivation
Plain English: 'inoperative' comes from the Latin 'operari' (to work) with the prefix 'in-' meaning 'not.' So one-engine-inoperative literally means 'one engine not working.' The hyphenated form is used as a single descriptor for a specific flight condition.
Why Pilots Care
Determines critical speeds and climb capability that pilots must know to maintain control and reach a safe altitude after an engine failure.
Grounding Statement
Picture a twin-engine airplane after one engine quits: the airplane can still fly, but it no longer has equal help from both sides.
Intuition Check
Do not assume one-engine-inoperative always means the engine is physically stopped. It means one engine is not providing usable power for flight.
Example Sentence 1
The pilot reviewed the one-engine-inoperative climb performance before departing from the high-altitude airport.
Example Sentence 2
The takeoff briefing always includes the one-engine-inoperative procedure for runway 27.