Definition
In ATC slot management, the status of a flight whose Controlled Time of Departure (CTD) or Controlled Time of Arrival (CTA) is no longer locked in and is once again open to adjustment by the traffic management system. An unfrozen flight can be re-sequenced, re-timed, or re-slotted as conditions change.
Plain English
The flight's assigned departure or arrival time is no longer fixed. The system can move it again if needed.
Context Anchor
Seen in arrival sequencing and traffic-management discussions, especially when controllers are managing how aircraft flow into a busy airport.
Derivation
From 'frozen,' meaning locked in place. In traffic management, a slot becomes 'frozen' when it is committed and protected from change; 'unfrozen' simply reverses that — the slot is open to movement again.
Why Pilots Care
Correct identification of unfrozen versus frozen precipitation affects aircraft performance, icing risk, runway braking, and the need for de-icing procedures.
Intuition Check
Unfrozen does not refer to ice on the aircraft. Here, it means a traffic-management plan is no longer locked and can be changed again.
Example Sentence 1
The flight's CTD was unfrozen when the ground delay program was revised, allowing dispatch to coordinate a new departure time.
Example Sentence 2
Pilots checked for unfrozen moisture on the wings before takeoff because the temperature was below freezing but no ice had formed.