Irregular Operations (IROPS) constitutes one of the most difficult problems the airline industry faces. Bad weather events can have a more devastating impact on airlines than they would on any other mode of intercity transport. Sometimes, an airline is forced to shut down operations at a key airport entirely. Even where the airport can remain open, capacity is reduced, delays build up, and eventually cancellations are required to get the airline back on schedule. The disruption will displace flight crews from their normal rotations, necessitating further corrective control actions to restore order to schedules, which in turn can disrupt operations still further.