Slot Time

A slot time is a specific time window assigned to a flight for takeoff or landing at a congested airport or through a congested airspace sector. Slots are a key mechanism for Air Traffic Flow Management (ATFM) and airport capacity management.

There are two types of slots:

• ATFM slots (CTOT): Calculated Takeoff Times assigned by flow management (Eurocontrol in Europe, ATCSCC in the US) to regulate traffic into congested areas. The aircraft must depart within a window of -5 to +10 minutes of the assigned CTOT
• Airport slots: Scheduled arrival/departure times allocated by a slot coordinator at capacity-constrained airports. These are seasonal allocations (summer/winter) governed by IATA guidelines and the principle of "grandfather rights" — airlines that have used a slot historically retain priority for future seasons

Airport slots at major hubs like London Heathrow, Tokyo Haneda, and New York JFK are extremely valuable. A pair of peak-hour slots at Heathrow has reportedly been traded for over $75 million.