Definition
A time specified by Air Traffic Control after which a clearance, when not yet acted upon, automatically becomes invalid. The ICAO usage typically applies this to a departure clearance: if the aircraft has not become airborne by the void time, the clearance is no longer valid and the pilot must contact ATC for further instructions.
Plain English
ATC gives you a clearance with a deadline attached. If you haven't taken off by that time, the clearance is dead and you have to call ATC before doing anything else.
Context Anchor
You may see this with clearances that must be used within a specific time, such as an IFR departure clearance from an airport without an operating control tower.
Derivation
‘Void’ comes from the Latin ‘vacuus’, meaning empty or without effect. In legal and procedural language, something that is voided becomes null — it no longer counts. Applied to a clearance, the void time is the moment the clearance becomes empty of authority.
Why Pilots Care
Using an expired clearance can result in loss of separation from other aircraft and is a violation of ATC instructions.
Intuition Check
Do not read void as meaning the clearance was never issued. It means the clearance stops being valid after the stated time if you have not acted on it.
Example Sentence 1
Cleared to the Bradford airport via direct, climb and maintain 5,000, clearance void if not off by 1415.
Example Sentence 2
If weather delays us past the clearance void time, we must call ATC for a new IFR clearance before taxiing.