Definition
An ATC IFR clearance issued at an uncontrolled airport that becomes invalid if the aircraft has not departed by a specific time stated in the clearance. The pilot must be airborne by that time, or the clearance is automatically cancelled and ATC must be contacted for a new clearance and release.
Plain English
Air traffic control gives you permission to fly your IFR plan, but only if you take off before the time they tell you. Miss that time and the permission is gone—you have to call them and get a new one before you go.
Context Anchor
Commonly heard when departing an airport where ATC cannot see or directly control the runway, especially when receiving an instrument departure clearance by radio or phone before takeoff.
Derivation
Clearance means official permission from air traffic control. Void comes from a word meaning empty or without legal force. In this phrase, void means the clearance loses its authority after the stated time if the aircraft has not departed.
Why Pilots Care
Missing the time forces the pilot to abort the takeoff sequence, contact ATC again, and wait for a replacement clearance, introducing delay and potential schedule disruption.
Analogy
It is like a reservation that expires at a specific time. If you do not use it before then, you cannot assume it still belongs to you.
Intuition Check
Do not read “off” as simply moving or rolling. Here, “off” means airborne; the aircraft must have taken off before the stated time.
Example Sentence 1
After receiving the IFR clearance by phone, the pilot read back, “Cleared to Asheville, clearance void if not off by one-five past the hour.”
Example Sentence 2
We held short after a ground delay and missed the void time, so we requested a new clearance from ground control.