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Ask the pilot: What is a slot time?

What does the flight crew do during a flight? How do they plan for bad weather? Who better to answer such questions than the pilots themselves.

What is a slot time?

Hi Petra,

Air Traffic Flow Management (ATFM) slots, or simply slots, are part of traffic flow management, which in Europe is centralized by Eurocontrol in Brussels. A slot, or slot time to be precise, is assigned due to restrictions in traffic flow at an airport or airspace (e.g. European airspace being congested at times, lack of staff/air traffic controllers, weather). It usually refers to the Calculated Take-Off Time (CTOT). The CTOT is the time, with a window of -5/+10 minutes, when the airplane is required to be at the runway, ready for departure. The slot time controls other standardized events, such as when the airplane can leave the gate (Target Off Block Time, TOBT) and when its engines can be started (Target Start-up Approval Time, TSAT).

If the airplane isn’t ready for departure, we risk missing the slot time, and thereby causing delay. This is the reason why passengers need to be seated well ahead of the slot time. We normally also send a message to air traffic control, stating that we are ready (all passengers onboard, all doors and hatches closed), hoping for an earlier slot time.

Rasmus Ilsø Olsen
Chief Pilot

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