Airline crew recovery

An airline schedule rarely operates as planned. It is often disrupted by maintenance problems or severe weather conditions. In a typical day, several flights may be delayed or cancelled, and aircraft and crews may miss the rest of their assigned flights. Airline coordinators have to find a minimal cost reassignment of aircraft and crews that satisfies all required safety rules, has little impact on passengers, and minimizes operational difficulties for the airline. The size of the entire schedule and the real-time nature of the problem rule out a full-scale optimization. It is necessary to reduce the complexity and the size of the problem before an optimization approach can be applied. In this paper, we focus on the problem of airline crew recovery. A new solution framework is developed, implemented, and tested. It provides, in almost real time, a recovery plan for reassigning crews to restore a disrupted crew schedule. Preprocessing techniques are applied to extract a subset of the schedule for rescheduling. A fast crew-pairing generator is built that enumerates feasible continuations of partially flown crew trips. Several branching strategies are presented that allow fast generation of integer solutions. We disturb the current schedule as little as possible, exploiting the fact that the planned schedule is optimal. The proposed framework has been implemented using tree-based data structures for efficient storage and data access. Computational results using a schedule from a major air carrier are presented.