I would like an option to put an aircraft into storage - where it would not go through maintenance checks. You could pay a small fee to put it into storage, and a small fee to retrieve it for later use (I have no idea how much this costs in the real world, but maybe 1 - 2% of the in game aircraft value would be okay). The fee should cover the work getting the aircraft ready for service again. The way things work now, you can either sell an aircraft you don't use, or you can scrap it (if it's over 15 y/o). But there's no way to place it in the Mojave desert for storage.
I've experienced several times that I've put aircraft for sale just to wait until they turn 15 y/o to be able to scrap them. It would be great to be able to put aircraft into storage to "save" them for later use due to commonality costs or other fleet strategy plans. For example if you've ordered a bunch of aircraft which will be your 4th type, you can put them in storage until you've received the last one and can replace your old fleet type. Also, in the real world, aircraft are utilized in markets that are cyclical. As far as I understand there will be more random (and planned) events in future worlds which might render surplus capacity.
The point is to put the plane into a "status quo" mode where it stays in the same maintenance condition until you pay a fee to bring it out from storage to use it, sell it, or scrap it. Regular maintenance schedule should not be running like it would if you just keep the plane in your fleet and not use it. (Right now you can turn off automatic C and D checks, but that will affect the whole fleet).
I imagine it could be done pretty straight forward, for example by placing a link or a box to tick right next to the "Sell Aircraft" and "Scrap Aircraft" on the aircraft page. Basically, a version of the selling aircraft code might be used, just that the airliner is not put up for sale, but goes into the same "For Sale & In Storage" database.