Allow more fleet types/aircraft as security for a loan.

[Pilot Oatmeal]

At the moment (it looks like) you cannot select more than one kind of fleet type to be used as a security for a loan if you have a decent amount of aircraft.

e.g. at the moment I can only select one type of my fleet to be used as a security. 

I think you should be able to use your entire fleet as a security for a large loan, including a mixture of aircraft.  We should be able to do this in the game.