The Impact of Uncertain Departure Delays on Flight Flexibility

The difficulty in synchronizing the activities of different actors and the existence of external constraints, e.g., weather conditions, usually produce some uncertainty on the exact time at which a flight operation can be executed. To cope with this uncertainty, aircraft operators need some flexibility when performing their flight operations, i.e., departing, arriving and flying through air sectors. We express this flexibility in terms of time windows, i.e, periods of time within which flight operations can be executed. The more flexible a flight is, the wider its time windows are. Time windows are centrally calculated and assigned to flights under the agreement that when a flight performs all its operations within the corresponding time windows, no downstream delay is caused to any other actor of the air traffic system. When a flight is unable to respect its time windows, some delay may also be caused to other flights. This paper investigates the effects on the system in terms of additional delay of the nonfulfillment of time windows at flight departures. It considers both airline collaboration and non-collaboration cases and proposes an algorithm that reduces this additional delay. This is achieved through the reassignment of capacity released by flights that are either delayed or have departed. We simulate a set of realistic instances where delays at departure are randomly assigned to flights after time windows have been determined. Our results show that the amount of additional delay generated by departure delays is limited, thus demonstrating the practical viability of the proposed approach.