I have another ideas, how about adding a requirement of deposit/security when leasing an aircraft. It is also a little bit related to creditability. For example, when you need to lease a A320, the lease must support by a A320 which is owned. When the airline unable to pay for the monthly rent, banker can takeover the owned A320 (since it is a security).
I think this world (S2) is a good place to observe different strategy of different players. Some ppl may sell their aircraft and change to smaller plane with lower maintenance cost. However, I don't agree with this strategy because the HR cost is still the same but you are making less profit!
You may have a look of the 1st one in ranking and you will know the trick for getting rich. But I do not agree with that unreasonable trick....