Errors should be cleared.
If you assign a different aircraft to the route it doesn't cancel the flights with the previous aircraft. It just makes it so that all future flights will be scheduled with the different aircraft. So in the future you would want to deactivate, then cancel the flights. Then you would be able to do a quick flight, or assign a different aircraft. Keeping in mind that if a flight is en-route already obviously it cant be cancelled.
If you assign a different aircraft to the route it doesn't cancel the flights with the previous aircraft. It just makes it so that all future flights will be scheduled with the different aircraft. So in the future you would want to deactivate, then cancel the flights. Then you would be able to do a quick flight, or assign a different aircraft. Keeping in mind that if a flight is en-route already obviously it cant be cancelled.
I am the developer of Airline Enterprise