Cancelled flight means a flight operation that was not operated, but was listed in an air carrier or a foreign air carrier's computer reservation system within seven calendar days of the scheduled departure.

Certificated air carrier means a U.S. carrier holding a certificate issued under 49 U.S.C. 41102 to conduct passenger service or holding an exemption to conduct passenger operations under 49 U.S.C. 40109.

Commuter air carrier means a U.S. carrier that has been found fit under 49 U.S.C. 41738 and is authorized to carry passengers on at least five round trips per week on at least one route between two or more points according to a published flight schedule using small aircraft as defined in 14 CFR 298.2.

Covered carrier means a certificated carrier, a commuter carrier, or a foreign air carrier operating to, from, or within the United States, conducting scheduled passenger service or public charter service with at least one aircraft having a designed passenger seating capacity of 30 or more seats.

Diverted flight means a flight which is operated from the scheduled origin point to a point other than the scheduled destination point in the carrier's published schedule. For example, a carrier has a published schedule for a flight from A to B to C. If the carrier were to actually fly an A to C operation, the A to B segment is a diverted flight, and the B to C segment is a cancelled flight. The same would apply if the flight were to operate from A to an airport other than B or C.

Excessive tarmac delay means a tarmac delay of more than three hours for a domestic flight and more than four hours for an international flight.

Foreign air carrier means a carrier that is not a citizen of the United States as defined in 49 U.S.C. 40102(a) that holds a foreign air carrier permit issued under 49 U.S.C. 41302 or an exemption issued under 49 U.S.C. 40109 authorizing direct foreign air transportation.

Gate arrival time is the instant when the pilot sets the aircraft parking brake after arriving at the airport gate or passenger unloading area. If the parking brake is not set, record the time for the opening of the passenger door. Also, for purposes of § 244.3 carriers using a Docking Guidance System (DGS) may record the official “gate-arrival time” when the aircraft is stopped at the appropriate parking mark.

Gate departure time is the instant when the pilot releases the aircraft parking brake after passengers have boarded and aircraft doors have closed. In cases where the flight returned to the departure gate before wheels-off time and departs a second time, the reportable gate departure time for purposes of this part is the last gate departure time before wheels-off time. In cases of a return to the gate after wheels-off time, the reportable gate departure time is the last gate departure time before the gate return. If passengers were boarded without the parking brake being set, the reportable gate departure time is the time that the last passenger door was closed. Also, the official “gate-departure time” may be based on aircraft movement for carriers using a Docking Guidance System (DGS). For example, one DGS records gate departure time when the aircraft moves more than 1 meter from the appropriate parking mark within 15 seconds. Fifteen seconds is then subtracted from the recorded time to obtain the appropriate “out” time.

Gate Return time means the time that an aircraft that has left the boarding gate returns to a gate or other position at an airport for the purpose of allowing passengers the opportunity to disembark from the aircraft.

Large hub airport means an airport that accounts for at least 1.00 percent of the total enplanements in the United States.

Medium hub airport means an airport accounting for at least 0.25 percent but less than 1.00 percent of the total enplanements in the United States.

Non-hub airport means an airport with 10,000 or more annual enplanements but less than 0.05 percent of the total enplanements in the United States.

Small hub airport means an airport accounting for at least 0.05 percent but less than 0.25 percent of the total enplanements in the United States.

Tarmac delay means the period of time when an aircraft is on the ground with passengers and the passengers have no opportunity to deplane.