Carrier route record

AASEA→MIA

American Airlines · Seattle to Miami

Flights: 423
Period: July 2025 to June 2026
Share of route: 36%
Carriers: 3

Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with American Airlines.

American on SEA to MIA sits in the middle of the pack with a B+. Close to three flights in four arrive on time by the DOT's definition, 3 points worse than the national rate of 77.6%. The late ones land about an hour behind schedule. That rests on 423 flights. The strongest carrier on the route with a full sample, Alaska Airlines, flew 391 at 78.8% on time.

The US average over the same twelve months is 77.6%, so there is little to separate American on SEA to MIA from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.

On time

75.1%

Arrivals under 15 minutes late, of 417 completed flights

Avg delay

58 min

Across delayed arrivals only, not all flights

Cancelled

0.71%

National rate is 1.81%

Whole route

77.3%

Every carrier on SEA to MIA, 1,179 flights

These figures cover 423 flights between July 2025 and June 2026. The median arrival is 4 minutes early, which is the part an average hides: most flights here are fine, and the on-time rate is decided by a tail of badly late ones. On-time means under 15 minutes late, the DOT's own threshold.

Carrier by carrier

American against every carrier on SEA to MIA

American flew 423 of the 1,179 flights on SEA to MIA, about 36% of it. Its 75.1% on time is 2 points worse than the route as a whole, which runs 77.3%. Ranked by on-time rate it is last of three carriers on the route, where the range runs from Alaska at 78.8% to American at 75.1%.

The two carriers here are closely matched: half a point 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.

On-time performance by carrier on SEA to MIA
Airline	Flights	On time	Avg delay	Cancelled	Grade
Alaska Airlines	391	78.8%	38 min	0.77%	B+
Delta Air Lines	365	78.2%	60 min	1.37%	B
American Airlines (this page)	423	75.1%	58 min	0.71%	B+

No carrier stands out. Alaska tops the table at 78.8%, half a point clear of the bottom, which is inside the range this kind of sample moves year to year.

Departure window

When American runs best on this route

Departure time is the single lever a traveller controls, and it moves the odds more than most people expect. Each bar below is the on-time rate for flights scheduled to leave inside that window, across 423 flights.

5am–8am—
8am–11am—
11am–2pm58 flights75.4%
2pm–5pm—
5pm–8pm—
8pm–5am365 flights75.0%

Scale runs 65% to 80%. Rows with fewer than 30 flights show a dash.

The overnight block holds up unusually well at 75.0% on time across 365 flights. Red-eyes fly into empty airspace and empty gates, and they are the first rotation of the aircraft's day rather than the last. The 8pm–5am window is the busiest, with 365 flights scheduled in it.

Across the year

American on SEA to MIA through the year

Darker means more delays. Figures are on-time percentages.January best, May worst

Delays peak in May, when the on-time rate falls to 61.9%. January is the strongest month at 87.1%. Moving a flexible trip across that boundary buys 25 points. June was the busiest month here, with 60 flights.

Across the week, Thursday is the strongest day at 82.0% on time and Saturday the weakest at 67.8%. 14 points is a smaller lever than departure hour, but it is free.

Delay causes

Why American runs late on this route

One category carries most of the weight here. Late-arriving aircraft accounts for 50% of the 5,999 delay minutes carriers reported, and the remaining four split what is left. The split is by minutes rather than by flights, so a few very long delays count for as much as many short ones.

Late-arriving aircraft
50%
Carrier
40%
National Airspace System
9%
Extreme weather
1%

50% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. That is a cascade, and cascades start small and grow through the day. Across 5,999 reported delay minutes here, that single category outweighs weather by 50 to one. It is the strongest argument for booking the first departure of the morning, when the aircraft has been sitting at the gate overnight with nothing to inherit. The split is drawn from 5,999 reported delay minutes.

The largest share of delay minutes, 40%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. Unlike weather, that is a management outcome, and it is the category where the gap between two carriers on the same schedule is genuinely earned. It accounts for 2,419 of the 5,999 delay minutes reported here.

Cancellations are rare at 0.71%, below the national 1.81% and low enough to earn the plus on the grade. Roughly one flight in 100 is called off; the risk here is arriving late, not not arriving.

Connections and stage length

What a delay here costs

7.2% 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 about an hour, which a normal layover absorbs.

At 2,724 miles this is transcontinental flying, and long routes get a quiet structural advantage. Scheduled block time on a flight this length carries more padding in absolute minutes, so a twenty-minute late departure often still becomes an on-time arrival. Read the on-time rate here as slightly flattering next to a short-haul route with the same operational quality.

The return leg is a different operation and performs like one: it runs 69.5% on time across 423 flights, 6 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 6 points of difference.

One caution: this is a thin sample. 423 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.

What to do with this

Booking American on SEA to MIA

Put together: treat all of this as provisional. 423 flights over twelve months is enough to clear this site's floor and not enough to be confident to better than a couple of points. The 75.1% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 417 completed flights over 12 months sit behind that.

Where to go next

Source: US DOT Bureau of Transportation Statistics, on-time performance data, July 2025 to June 2026. Last updated 15 September 2026; recomputed monthly. How this data is collected.

Key figures