In the game I think there should already be a system along with the airport control tower, which is to configure some time in our absence and in that certain time the game runs alone, but of course, in this configuration we spend time vs X value in money of the game itself. Note: the reason is to make it more realistic I think, and not to stay that lot of planes to go down and zero planes in the airspace. That’s a suggestion, maybe you already have something in mind.