ATFM departure slots are allocated centrally by the Network Manager to hold aircraft on the ground when there is an envisaged imbalance between demand and capacity at airports or en-route.
ATFM slot adherence measures the share of take-offs outside the allocated ATFM window. Within the EU, the monitoring of ATFM slot adherence is required by Regulation (EU 2010). ATS units are required to provide information on non-compliance for airports where non-adherence equals or exceeds 20% of regulated departures.