I know that this feature has been requested, but i want to show my thoughts about it. First of all, you need to select a main airline. You can have more that one. And if you have one, it will be 20% of all flights or you can just set the frequency to normal airlines with my tool (Idea) Ideas pack (Idea 2).
You don’t need to set the main airlines only for frequency, you can do it (frequency) with tool (maybe in future.) I think that main airlines should be allowed to store planes in hangars with foundation and the hangar tool.
It would also bring new type of employees: The hangar employees. they would take care of the planes, help with rolling them inside. Eventually inspect them.
Well, general task of hangars is to store planes waiting for flights.
What do you think about it?