I personally think that there is a fairly strong argument that all airline contracts are illusory and therefore the contract is void.

Airlines have purposefully written contract to be non-commital their part. Airline can cancel routes, cancel flights, or change schedules at will. They are under no obligation to hold up their end of the bargain. Instead they just refund money received. With any other industry or contract, a blatant breach such as a schedule change would result in breach of contract and the breacher being responsible for subsequent damages.

Airlines have specifically worded the contract in such a way that they are really not bound to do anything. So I think there is a very good argument that the contract is illusory.