The research has focused on building of the mathematical model and the optimization part. Creating the schedule. The resource allocation problem has been split into 4 subproblems a-d which have been solved seperately. Preferably they should be integrated but generally such models are too complicated, some attempts towards integrations have though been made. Robust planning- planning assuming disruptions, has proven to be very tough.
Airlines are the beggest test bag for large scale integer programming in industry.
The basic model used is a time line network and the modeller needs to track 3 flow streams, airplanes, passengers and crews. Usually a weekly time line is needed but people mostly use a daily time line. Usually airlines have the same schedule for all weekdays but somewhat different on weekends. Airlines plan their US domestic flights in a hub and spoke model. Airlines usually have 3-7 hubs and if you want to fly between two non hub cities you usually have to change flights in a hub city.