Optimizing aircrew recovery considering long connections: A column generation based approach

Severe weather and air traffic flow control can often cause flight delays and disrupt the crew schedules, resulting in a too-short or a too-long connection between flights. Short connections need to be adjusted to ensure the airline’s smooth operations, while the long connection whose duration is only a bit lower than the threshold enabling the crew to leave the flying zone for a rest at airport terminals can be quite inefficient, as the crew’s ground standby is viewed as working all the time without executing any flight which adds to the shortage of crew resources. Thus, we propose a method of delaying flights to the point enabling crews to leave for a rest, which helps save the available working hours. The difficulty lies in the trade-off between the additional swap or delay cost in creating long connections and the possible global cost decrease due to savings in available working hours brought by long connections, which calls for optimization. In this paper, we introduce the crew recovery problem for one day of operation taking long connections into account. The problem is mathematically formulated as an arc-based integer programming model and a set partitioning model in order to determine the optimal flight recovery schedule and the crew reassignment. A column generation based solution approach is developed and the sub-problems consisting of the resource-constrained shortest path problem are solved by a labeling algorithm. Computational experiments based on real-world data from a major Chinese airline confirm the effectiveness and efficiency of the solution approaches. It is also demonstrated the save of available working hours resulting from adaptively creating long connections would decrease the recovery cost by about 18.87%–74.88%.