Definition
In the context of inoperative equipment under an MEL or other approved authorization, the condition of an aircraft component or system that has been intentionally rendered non-functional by an approved procedure — typically by removing power, disconnecting, securing, or physically isolating it — so that it cannot operate or affect other systems during flight.
Plain English
A piece of equipment has been deliberately turned off or disconnected in a controlled way so it can't run and can't interfere with anything else while you fly.
Context Anchor
Seen when deciding whether an aircraft may be flown with a piece of equipment that is not working.
Derivation
From Latin 'activus' (active, doing) with the prefix 'de-' meaning 'away from' or 'reverse of.' Literally 'made not active.' In aviation it carries a specific procedural weight: the item isn't merely switched off — it has been put into a defined inoperative state by an approved method.
Why Pilots Care
Ensures inoperative items cannot create hazards or distract the crew, maintaining compliance and flight safety.
Intuition Check
Do not read deactivated as simply “not working.” In this context, it means a deliberate approved step has been taken to keep the item from operating.
Example Sentence 1
The autopilot was deactivated and placarded inoperative per the MEL before the flight departed.
Example Sentence 2
All deactivated systems must be clearly marked so the crew knows they are not available.