What is a CTOT slot? Why your plane is ready but not allowed to leave

You’re on board. The doors are closed. The captain comes on: “We’re just waiting for our slot, folks.” Twenty minutes later, you’re still at the gate.

Nobody has forgotten about you. Your flight has been given a CTOT, and until that time comes round, it isn’t going anywhere.

What a CTOT actually is

CTOT stands for Calculated Take-Off Time. In Europe it’s issued by the EUROCONTROL Network Manager, which looks at every flight plan across more than 40 countries at once.

When a piece of airspace or an airport is expected to get more traffic than it can safely handle, a regulation is put in place: a cap on how many flights can enter per hour. Flights heading into that bottleneck get a take-off time that spreads them out.

Your flight then has to take off within a small window around its CTOT, normally from 5 minutes before to 10 minutes after. Miss it, and the airline has to ask for a new one, which may be much later.

Why not just take off and wait in the air?

Because fuel, noise and safety. Holding a full aircraft in the air costs fuel and adds traffic to airspace that is already busy. Holding it on the ground costs nothing but your patience.

It’s the same logic as a bouncer at a club: better a queue outside than a crush inside.

Why do slots happen?

The reason is attached to every regulation. The common ones:

Reason	What it means
ATC capacity	More flights planned than the sector can take
ATC staffing	Fewer controllers on duty than the plan needed
Weather	Storms or strong wind cut how many aircraft fit through
Airport	The runway at your destination (or departure) is full
Industrial action	A strike somewhere along your route

Airlines record these causes with standard delay codes. The 80s range covers delays caused by air traffic flow management.

Does a slot delay mean I can claim?

Compensation under UK261 and EU261 starts when you arrive 3 hours late or more. The question is whether the airline can show the cause was an extraordinary circumstance.

• Controller strikes still count as extraordinary. No compensation, but you’re still owed meals, drinks and, for long delays, a choice of rerouting or a refund.
• Bad weather usually counts, if it really affected your flight.
• “ATC restrictions” in general are no longer an automatic get-out for EU261 flights. Since the October 2026 EU court ruling, the airline has to show it could not have avoided the delay. UK courts are not bound by new EU rulings, so for UK261 flights the position may be different.

Ask the airline for the delay reason in writing. Then check your case.