Expect Departure Clearance Times (EDCT)
ASPM receives records containing Expect Departure Clearance Times (EDCT) from its daily TFMS data feed provided by the FAA Data Repository. EDCT is the runway release time (“Wheels Off”) assigned to aircraft due to Traffic Management Initiatives (TMIs) that require holding aircraft on the ground at the departure airport. The ASPM calculated EDCT Departure Delay is the additional time the flight was held on the ground past its planned wheels-off departure time, due to the TMI.
When a concern is raised about the traffic situation at a specific airport(s) or sector(s), a conference is held among affected air traffic facilities, the ATCSCC, and the primary system customers to discuss alternatives and modeled scenarios. If the decision is made to implement a TMI requiring aircraft to be held on the ground, EDCTs will be sent to Collaborative Decision Making (CDM) members, airlines, and NAS computers, and an advisory is issued stating that a TMI has been implemented. Aircraft operators are expected to depart within (5) minutes of the EDCT departure time. If an aircraft is late, air traffic controllers are required to call the ATCSCC to get a new EDCT. This could mean additional delay for the aircraft and missed slot opportunities for other aircraft. All major airlines and some large business aviation companies have a connection to the Flight Schedule Monitor (FSM) and receive their EDCTs electronically.
How ASPM Calculates EDCT Delay
Through September 2011, ASPM calculated EDCT Departure Delay as the difference between the Controlled Departure Time (EDCT Off) and the FAA Planned Wheels Off Time. If the FAA Planned Off time is not present in TFMS record, it is estimated as the carrier filed P-time (flight plan gate out time) plus the Unimpeded Taxi Out Time (for that airport, carrier, and hour).
Starting October 1, 2011, ASPM changed its EDCT Departure Delay calculation to the lesser of 1) The difference between the EDCT Off Time and the earlier of the FAA Planned Wheels Off and the Scheduled Airport Departure Time (Scheduled Gate Out + Unimpeded Taxi Time); and 2) The difference between the EDCT Off Time and the Flight Plan Airport Departure Time (the carrier filed flight plan time + the Unimpeded Taxi Time). Step 1 provides an upper limit on EDCT Departure Delays and reduces the reliance on the FAA Planned Wheels-Off Time. Step 2 generally results in a smaller EDCT Departure Delay and therefore is applied to the flight records in most cases.
This change was made to compensate for an unexplained shift in the FAA Planned Wheels Off Time, which started in November 2010 and resulted in artificially low EDCT Departure Delay times. The change was applied retroactively to October 2011, but the EDCT Departure Delays from November 2010 through September 2011 remain lower than expected.
The shift in the Planned Wheels Off times occurred at the same time that TFMS implemented a fix to its processing of Field 10. It is suspected that the shift was an unintended consequence of the TFMS processing adjustment; further investigation is ongoing.
How ASPM Summarizes EDCT Measures
ASPM sums EDCT Delay by airport and carrier and can report totals and averages in a variety of ways, as it does with other delays. It also reports this delay for individual flights.
ASPM also calculates the number of early and late EDCT Departures, as well as early and late EDCT Arrivals. This means ASPM tracks the number of Wheels Off prior to EDCT and after EDCT. In addition, ASPM tracks how many flights arrive prior to or after the expected arrival time based on EDCT.
These counts provide valuable information about how well the FAA is able to anticipate the duration of delays and what flights were affected.