Definition
The specific clock time by which an aircraft must be airborne on an IFR clearance issued at an airport without an operating control tower. If the aircraft is not airborne by that time, the clearance is automatically cancelled (becomes void), and the pilot must contact ATC to obtain a new clearance.
Plain English
When ATC gives you an IFR clearance from an uncontrolled airport, they include a deadline. You must be off the ground by that exact time. Miss it, and the clearance no longer exists — you have to call ATC and start again.
Context Anchor
Used when departing from an airport without an operating control tower, usually when a pilot receives a clearance from air traffic control by radio or phone before takeoff.
Derivation
Void comes from the Latin vacuus, meaning 'empty.' A clearance that has gone past its void time is empty — it no longer carries any authority.
Why Pilots Care
Missing the void time prevents legal departure on that clearance, requiring a new one and possible delays.
Intuition Check
Do not read void time as a period of empty or unused time. In this context, it is the time when your clearance becomes invalid if you have not departed.
Example Sentence 1
Clearance delivery issued the IFR clearance with a void time of 1415Z, so the pilot taxied promptly to be airborne with a few minutes to spare.
Example Sentence 2
If you miss your void time at a non-towered airport, you must obtain a new IFR clearance before departing.