The computational results are old. The fleet assignment problem may be considered a solved problem. Here we need to restrict to the same plane being used midday and late night since the crews are not in the model. The same crew can not be used to fly different types of planes. Revenue is considered to be flight leg based but most passengers take more than one flight in the hub based model.
Bid price is a dual variable.
Wouldn't expect uniqueness of dual solution, another possible version would be to have linear concave functions based on probability. They don't have so much degeneracy but no dual. This is definetely an open area. The airlines impose the condition that of all flight legs given to a given plane each plane should fly every one. It is possible to combine the rotation and the fleeting problem.