Many things go into whether or not a flight arrives on time. American’s management argues that what they can most control is whether the flight departs on time, and if it does, that’s going to be the single biggest driver of on time arrivals.
So American Airlines management is singularly focused on what they refer to as “D0” — departing exactly the minute that a flight is scheduled to depart (the government considers a flight to be ‘on time’ when it arrives within 15 minutes of schedule).