Aircraft have to be scheduled for various maintenance checks such as "A", "B", "C", and "D" (which are the heaviest maintenance checks and take them out of serv

Aircraft have to be scheduled for various maintenance checks such as "A", "B", "C", and "D" (which are the heaviest maintenance checks and take them out of service for many days/weeks). They're of course checked by the Ramp Crew and also receive a pre-flight walk around by the pilots before take-off. The only wait time is if there is a necessary repair to deal with a warning/indicator light and related repair time, hopefully does not take the aircraft out of service. Better out of service than break down in-air.