F9MDW→ATL

Frontier flew 599 of the 3,528 flights on MDW to ATL, about 17% of it. Its 71.8% on time is 8 points worse than the route as a whole, which runs 79.8%. Ranked by on-time rate it is last of three carriers on the route, where the range runs from Delta at 86.9% to Frontier at 71.8%.

The choice of carrier is not cosmetic here. Delta Air Lines arrives on time 86.9% of the time; Southwest Airlines manages 76.7%. Sample sizes sit next to every figure, because a two-point gap across 1,546 flights means less than a ten-point one.

7.1% of arrivals land an hour or more late, close to the national 8.1%. That is the figure that decides a connection, and it says a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route last roughly 50 minutes, which a normal layover absorbs.

The 591 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 65.2% on time across 599 flights, 7 points below 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. 599 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.