Smart that you want to keep one each time. Good for events and small quests.
How come it doesn't work that way with the reserve hangar?
I use the trick with the open extra slot and buying/selling the 200 coin plane to move planes around. Works just fine...
(More info about the reserve hangar out of the guides section.)
I bought a Jet and put a Turboprop plane in the Reserve Hanger. When the Jet broke after its first flight, I tried to put the Turboprop plane in the hanger, and the broken Jet in the Reserve Hanger, so it wouldn't be in the way while I finished upgrading my Repair Base, but it said I would have to throw away the broken plane to use the other one. The only way it would let me take the Turboprop plane out of the Reserve Hanger was to sell my last Powerful Propeller-Driven plane to create an empty hanger for it to go in. The trick is good for keeping an expensive plane in storage if you need to buy a cheap plane for a quest. It doesn't help if you want to keep a cheap plane in storage unless you can upgrade your Control Tower and buy a new hanger every time you need to use it.