F9ATL→IAD

Frontier flew 640 of the 3,979 flights on ATL to IAD, about 16% of it. Its 63.0% on time is 14 points worse than the route as a whole, which runs 76.5%. Ranked by on-time rate it is last of four carriers on the route, where the range runs from Republic at 85.7% to Frontier at 63.0%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.

The two carriers here are closely matched: 4 points separate the best from the worst. At that spread, schedule and price are better tie-breakers than reliability. Sample sizes are shown so you can see which rows are worth weighing.

For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 18.2% of arrivals land a full hour or more behind schedule, against 8.1% nationally. A 45-minute layover does not survive that, and no amount of walking quickly changes it. Ninety minutes is the honest minimum here, and two hours if the onward flight is on a separate ticket.

The 534 miles between these two airports put this in the middle of the US network, around two and a half to three hours of block time. That is enough cruise to absorb a ten-minute late pushback and not enough to absorb thirty. It is also long enough that the aircraft usually flies three or four legs a day rather than six, which slows how fast delay compounds.

The return leg is a different operation and performs like one: it runs 69.9% on time across 639 flights, 7 points above this direction. Departure banks, aircraft rotations and the congestion at each end all differ, so scoring the two directions together would average away a real 7 points of difference.

One caution: this is a thin sample. 640 flights over twelve months is enough to clear this site's floor but not enough to pin the rate down tightly, and a single bad week moves it by more than a point. Treat the grade as a rough reading.