Definition
The time, expressed in Coordinated Universal Time (UTC), at which an aircraft is scheduled to or actually does depart on a flight, as filed on a flight plan or assigned by air traffic control.
Plain English
The clock time, in UTC, when the flight starts — either the time you plan to leave or the time ATC tells you to leave.
Context Anchor
You may see this term in flight plans, ATC timing, flight tracking, and records of when a flight actually began.
Derivation
Departure comes from an older word meaning “to part” or “to leave.” In this aviation use, the aircraft has not truly departed until it leaves the ground.
Why Pilots Care
Determines slot assignments, ATC handoff timing, fuel calculations, and compliance with filed departure windows.
Intuition Check
Do not assume departure TIME means when the pilot starts the engine, begins taxiing, or receives a clearance. In this FAA glossary sense, it means the moment the aircraft becomes airborne.
Example Sentence 1
He filed a proposed departure time of 1530Z, then called clearance delivery ten minutes prior to activate the flight plan.
Example Sentence 2
ATC noted the actual departure time as 1423 when the aircraft became airborne.