Swapping A/C on route

[Mombone78]

  Is it possible to assign another a/c on a route when primary a/c/ goes down for maintenance

[Tha_Ape]

It is possible, yes. The green arrow below a plane's schedule.
However, this is usually useless, except in the very early stages of the game. And when you get past 100 a/c, it becomes almost unmanageable.