Carrier route record
AASEA→MIA
American Airlines · Seattle to Miami
- Flights
- 475
- Period
- September 2025 to August 2026
- Share of route
- 39%
- Carriers
- 3
Historical statistics for September 2025 to August 2026, not live status. For today’s flights, check with American Airlines.
American on SEA to MIA lands a B+, about a point better than the national rate of 77.3%. About one flight in five arrives 15 minutes late or worse, and those flights are late by about an hour on average. That rests on 475 flights. The strongest carrier on the route with a full sample, Delta Air Lines, flew 365 at 80.7% on time.
The US average over the same twelve months is 77.3%, 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.
Key figures
On time
78.4%
Arrivals under 15 minutes late, of 468 completed flights
Avg delay
68 min
Across delayed arrivals only, not all flights
Cancelled
0.84%
National rate is 1.89%
Whole route
79.7%
Every carrier on SEA to MIA, 1,231 flights
These figures cover 475 flights between September 2025 and August 2026. The median arrival is 8 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.
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Carrier by carrier
American against every carrier on SEA to MIA
American flew 475 of the 1,231 flights on SEA to MIA, about 39% of it. Its 78.4% on time is about level with the route as a whole at 79.7%. Ranked by on-time rate it is last of three carriers on the route, where the range runs from Delta at 80.7% to American at 78.4%.
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.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Delta Air Lines | 365 | 80.7% | 65 min | 1.37% | B |
| Alaska Airlines | 391 | 80.5% | 40 min | 0.26% | B+ |
| American Airlines (this page) | 475 | 78.4% | 68 min | 0.84% | B+ |
No carrier stands out. Delta tops the table at 80.7%, half a point clear of the bottom, which is inside the range this kind of sample moves year to year.
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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 475 flights.
- 5am–8am—
- 8am–11am—
- 11am–2pm110 flights81.5%
- 2pm–5pm—
- 5pm–8pm—
- 8pm–5am365 flights77.5%
Scale runs 70% to 85%. Rows with fewer than 30 flights show a dash.
The 11am–2pm window is the strongest at 81.5% on time. The full set of windows spans 4 points.
Across the year
American on SEA to MIA through the year
Delays peak in May, when the on-time rate falls to 61.9%. August is the strongest month at 88.5%. Moving a flexible trip across that boundary buys 27 points. July was the busiest month here, with 62 flights.
Across the week, Thursday is the strongest day at 82.6% on time and Saturday the weakest at 71.2%, a spread of 11 points.
Arrival by arrival
How late American on SEA to MIA runs when it is late
American on SEA to MIA often beats the schedule: 165 of 468 completed flights, 35%, arrived 15 minutes or more early. The 101 late arrivals split 34 under half an hour, 38 between 30 and 60 minutes, and 29 an hour or more.
- 15+ min early165 flights35.3%
- Within 15 min202 flights43.2%
- 15–29 min late34 flights7.3%
- 30–59 min late38 flights8.1%
- 1–2 hours late19 flights4.1%
- 2+ hours late10 flights2.1%
Scale runs 0% to 100%.
Share of 468 completed flights by arrival against schedule.
A late pushback is often recovered here: of 134 departures that left 15 minutes late or more, 45 still arrived on time. 12 flights left on time and still arrived late.
The worst days
Worst days for American on SEA to MIA
The latest arrival of the period was on 21 July 2026, 15 hours 58 minutes behind schedule; most of its delay minutes were filed as carrier-caused (crew, maintenance, fuelling, baggage). The same cause led on three of the five worst days.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 21 July 2026 | 15 hours 58 minutes | Carrier |
| 17 January 2026 | 10 hours 54 minutes | Carrier |
| 16 July 2026 | 4 hours 35 minutes | Late-arriving aircraft |
| 1 April 2026 | 3 hours 28 minutes | Carrier |
| 26 June 2026 | 3 hours 2 minutes | Late-arriving aircraft |
Delay causes
Why American runs late on this route
Late-arriving aircraft accounts for 46% of the 6,853 delay minutes carriers reported here, and the remaining four split what is left.
- 46%Late-arriving aircraft
- 44%Carrier
- 9%National Airspace System
- 1%Extreme weather
46% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 6,853 reported delay minutes here, that single category outweighs weather by 46 to one. The split is drawn from 6,853 reported delay minutes.
The largest share of delay minutes, 44%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 3,006 of the 6,853 delay minutes reported here.
Cancellations are rare at 0.84%, below the national 1.89% 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
6.2% of arrivals land an hour or more late, close to the national 8.3%, so 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 72.5% on time across 475 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. 475 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. 475 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 78.4% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 468 completed flights over 12 months sit behind that.
Related
Where to go next
- SEA to MIA, every carrier
- American on MIA to SEA, the return leg
- Delta Air Lines on SEA to MIA80.7%
- Alaska Airlines on SEA to MIA80.5%
- American Airlines network-wide record
- Seattle-Tacoma International (SEA) delay statistics
- Miami International (MIA) delay statistics
- Why the first flight of the morning is statistically safest
- Worst months to fly in the US, ranked by the data
Source: US DOT Bureau of Transportation Statistics, on-time performance data, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.