NKBOS→MIA

Spirit flew 187 of the 3,417 flights on BOS to MIA, about 5% of it. Its 54.0% on time is 24 points worse than the route as a whole, which runs 77.7%. Ranked by on-time rate it is number four of five carriers on the route, where the range runs from American at 82.3% to Republic at 47.6%. Two of those carriers flew fewer than 365 flights here, so treat their positions as rough.

The choice of carrier is not cosmetic here. American Airlines arrives on time 82.3% of the time; Delta Air Lines manages 72.1%. Sample sizes sit next to every figure, because a two-point gap across 890 flights means less than a ten-point one.

For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 27.8% 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 1,258 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 runs 54.3% on time across 186 flights, within half a point of this direction. The two legs are scored separately because they usually differ; on this city pair they happen not to.

One caution: this is a thin sample. 187 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.