Would it be possible to create a constraint for scheduling maintenance? I have noticed that the majority of my maintenance is scheduled for off peak hours and days. In the RW this would create added cost due to extra staff, OT, shift premiums, etc. Also, it's unlikely that your maintenance facility would accomodate all your a/c. It could work similarily to slots at an airport. Of course each a/c could have different values according to the complexity of the engine, number of engines, size of a/c etc. Later in the game you could purchase new facilities (or new features) to expand your capacity. Also, you could rent facilities (especially in the beginning) or rent out your facilities if you have too much capacity. An added feature could be to allow alliance members to use your facility if they need maintenance away from their hub.
These features would provide more realism but also add a new level of complexity to an already complex game. Bring it on!