Plain English Meaning
A part of the aircraft that has stopped working properly. The pilot needs to figure out whether they can keep flying without it, and if so, what extra care is required.
Full Definition
An aircraft instrument, system, or piece of equipment that is not functioning correctly and cannot be relied upon to provide accurate information or perform its intended task. When a component is identified as inoperative, the pilot must determine whether the flight can legally and safely continue, often by referencing the aircraft's Minimum Equipment List (MEL) or applicable regulations.
Context Anchor
Seen when discussing aircraft system or instrument failures, such as an analog instrument that stops giving reliable information in flight.