Carrier route record

ASSTL→SEA

Alaska Airlines · St. Louis to Seattle

Flights: 781
Period: July 2025 to June 2026
Share of route: 88%
Carriers: 2

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

Alaska on STL to SEA lands a B, 3 points better than the national rate of 77.6%. About one flight in five arrives 15 minutes late or worse, and those flights are late by about 50 minutes on average. That is a workable record, not a spotless one. That rests on 781 flights, with a median arrival 5 minutes early.

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

On time

80.7%

Arrivals under 15 minutes late, of 771 completed flights

Avg delay

49 min

Across delayed arrivals only, not all flights

Cancelled

1.02%

National rate is 1.81%

Whole route

77.6%

Every carrier on STL to SEA, 884 flights

These figures cover 781 flights between July 2025 and June 2026. The median arrival is 5 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

Alaska against every carrier on STL to SEA

Alaska flew 781 of the 884 flights on STL to SEA, most of the route. Its 80.7% on time is 3 points better than the route as a whole, which runs 77.6%. Ranked by on-time rate it is first of two carriers on the route, where the range runs from Alaska at 80.7% to Southwest at 54.4%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.

Only one carrier clears this site's 365-flight floor here, so there is no comparison to draw. The table below is the full picture.

On-time performance by carrier on STL to SEA
Airline	Flights	On time	Avg delay	Cancelled	Grade
Alaska Airlines (this page)	781	80.7%	49 min	1.02%	B
Southwest Airlinesthin sample	103	54.4%	43 min	0.00%	F+

Flight by flight

Alaska flight numbers on STL to SEA

AS 47307:0090.3% · 321 flights

Departure window

When Alaska runs best on this route

Departure time matters more here than the choice of carrier. The gap between the best and worst window is 30 points, against half a point between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am322 flights90.3%
8am–11am—
11am–2pm—
2pm–5pm308 flights80.4%
5pm–8pm130 flights60.0%
8pm–5am21 flights—

Scale runs 50% to 95%. Rows with fewer than 30 flights show a dash.

The 5pm–8pm window is where this operation falls apart: 60.0% on time, against 90.3% for the 5am–8am slot. By evening the aircraft flying these rotations have absorbed a full day of small delays and there is no slack left to recover in. The 5am–8am window is the busiest, with 322 flights scheduled in it.

Across the year

Alaska on STL to SEA through the year

Darker means more delays. Figures are on-time percentages.April best, December worst

December is the weak month at 54.7% on time, against 94.8% in April. Winter delays cluster: a single storm system can account for most of a month's shortfall, so an average December hides both very good weeks and genuinely unflyable days. July was the busiest month here, with 92 flights.

Across the week, Wednesday is the strongest day at 86.3% on time and Saturday the weakest at 71.4%. 15 points is a smaller lever than departure hour, but it is free.

Delay causes

Why Alaska runs late on this route

Carriers report a reason for every delay minute they cause, in five DOT categories. The split below is by minutes, not by number of flights, so a handful of very long weather delays weighs as much as many short ones. It covers 7,321 reported delay minutes.

Carrier
35%
Late-arriving aircraft
35%
National Airspace System
26%
Extreme weather
4%
Security
1%

35% 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 7,321 reported delay minutes here, that single category outweighs weather by 9 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 7,321 reported delay minutes.

The largest share of delay minutes, 35%, 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 2,583 of the 7,321 delay minutes reported here.

Cancellations sit at 1.02% against a national 1.81%, which is ordinary. Diversions add another 0.26%.

Connections and stage length

What a delay here costs

Badly late arrivals are rare here: only 3.2% land an hour or more behind schedule, against 8.1% nationally. Connections built on this flight are about as safe as US domestic connections get, though a cancelled flight still ignores every layover you give it.

At 1,709 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 runs 82.2% on time across 780 flights, within 2 points 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. 781 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 Alaska on STL to SEA

Put together: treat all of this as provisional. 781 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 80.7% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 771 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