Route profile
STL→SEA
Flight reliability, delays and best times to fly from St. Louis to Seattle, 1,709 miles.
Right now
Aviation weather is not currently a factor.
Aviation weather is not currently a factor.
Route reliability
July 2023 – July 2026
Better than 79% of comparable major US routes (4,598 compared)
Calculated from 2,717 flights. How this is calculated
STL → SEA arrives on time 79.7% of the time; the return trip, SEA → STL, arrives on time 78.2% of the time.
STL → SEA spends 28.9 minutes on the ground on a 1,709-mile trip: 16.6 minutes from pushback to wheels-up at STL and 12.3 minutes from touchdown to gate at SEA.
Source: US DOT Bureau of Transportation Statistics · Data covering July 2023 – July 2026
What stands out
The airline matters unusually much on this route, a wider carrier-to-carrier gap than 97% of 2,692 comparable routes.
Alaska Airlines arrived on time 82.1% of the time, against 59.6% for Southwest Airlines, flying the exact same route.
Source: FlyerIntel analysis of US DOT BTS data · July 2023 – July 2026 · Ranked against every other route with the same kind of figure and at least 2,692 in the comparison.
When it goes wrong
July 2023 – July 2026
30 min late
against a median of 5 min early
Percentiles over 2,717 operations; cancelled and diverted flights are counted separately.
Will your connection be tight enough?
Layovers at SEA after arriving from STL.
| Connection time | Chance of missing | Reads as |
|---|---|---|
| 30 min | 39% | Likely to miss |
| 45 min | 19% | High risk |
| 60 min | 9.6% | Some risk |
| 90 min | 3.6% | Low risk |
| 120 min | 2.3% | Low risk |
This is one leg of a connection. Gate changes and the next flight's own schedule matter too. And a connection can fail before delay is even the question — this route cancels 0.88% of the time and diverts 0.11% of the time, which a late arrival never shows up in.
Chance of missing is the share of 2,690 arrivals on this route that landed later than the connection time less 30 minutes to reach the next gate.
The worst tenth of arrivals on this route land at least 30 minutes late (90th-percentile gate arrival delay), over 2,717 operations.
Any other layover length: connection checker.
Best time to fly
STL → SEA flights departing 5–9 AM arrived on time 88.1% of the time, against 65.4% for 6–9 PM departures, a gap of 22.7 percentage points.
By departure window
By departure hour
- 12 AM to 5 AM: too few flights to score
- 6 AM: 92.3% on time from 274 flights
- 7 AM: 86.6% on time from 728 flights
- 8 AM to 1 PM: too few flights to score
- 2 PM: 83.9% on time from 601 flights
- 3 PM: 77.6% on time from 404 flights
- 4 PM to 6 PM: too few flights to score
- 7 PM: 66.1% on time from 346 flights
- 8 PM to 11 PM: too few flights to score
Departure windows with fewer than 120 flights are not scored.
Why STL → SEA runs late
July 2023 – July 2026
the inbound aircraft was late, so this flight started late
crew, maintenance, boarding and fueling, all within the carrier’s control
airspace and airport capacity, including weather-driven flow control
weather severe enough to stop this flight specifically
screening or terminal security incidents
Share of the delay minutes US DOT attributed to each cause for STL → SEA. Only delays of 15 minutes or more are attributed.
Late-arriving aircraft is the largest cause on STL → SEA, at 36.2%: flights here mostly leave late because the plane came in late, and the day shows it: 5–9 AM departures arrived on time 88.1% of the time and 6–9 PM departures 65.4%.
Airlines on this route
Carriers with at least 200 flights, by the airline that operated each one.
| Carrier | Flights | On time | Cancelled | Median delay | Severe |
|---|---|---|---|---|---|
| Alaska Airlines | 2,440 | 82.1% | 0.98% | -7 min | 3.5% |
| Southwest Airlines | 277 | 59.6% | 0.00% | 9 min | 5.8% |
Alaska Airlines flew 89.8% of the 2,717 flights listed.
Alaska Airlines arrived on time 22.5 percentage points more often than Southwest Airlines on this route.
Flights on this route
Flight numbers with at least 600 operations here and still on the schedule.
| Flight | Scheduled | Operations | On time |
|---|---|---|---|
| AS473 Alaska Airlines | 7:00 AM | 941 | 89.0% |
Weekly and seasonal patterns
By day of week
Monday is historically the most reliable day and Saturday the least, a gap of 8.2 percentage points.
By month
- Jan to Feb: no data
- Mar: 88.6%
- Apr: 89.2%
- May: 74.7%
- Jun: 69.1%
- Jul: 73.8%
- Aug: 77.2%
- Sep: 85.7%
- Oct: 89.1%
- Nov: 87.8%
- Dec: 76.1%
June is historically the weakest month and April the strongest, a spread of 20.1 percentage points.
Reliability over time
July 2023 – July 2026
- July 2023: too few flights to score (91)
- August 2023: too few flights to score (93)
- September 2023: too few flights to score (89)
- October 2023: too few flights to score (63)
- November 2023: too few flights to score (58)
- December 2023: too few flights to score (56)
- January 2024: too few flights to score (38)
- February 2024: too few flights to score (37)
- March 2024: too few flights to score (56)
- April 2024: too few flights to score (60)
- May 2024: too few flights to score (78)
- June 2024: too few flights to score (117)
- July 2024: 80.0% from 122 flights
- August 2024: too few flights to score (110)
- September 2024: too few flights to score (100)
- October 2024: too few flights to score (60)
- November 2024: too few flights to score (50)
- December 2024: too few flights to score (54)
- January 2025: too few flights to score (34)
- February 2025: too few flights to score (38)
- March 2025: too few flights to score (52)
- April 2025: too few flights to score (59)
- May 2025: too few flights to score (79)
- June 2025: too few flights to score (116)
- July 2025: 67.2% from 123 flights
- August 2025: too few flights to score (111)
- September 2025: too few flights to score (98)
- October 2025: too few flights to score (61)
- November 2025: too few flights to score (50)
- December 2025: too few flights to score (54)
- January 2026: too few flights to score (38)
- February 2026: too few flights to score (37)
- March 2026: too few flights to score (53)
- April 2026: too few flights to score (60)
- May 2026: too few flights to score (81)
- June 2026: too few flights to score (118)
- July 2026: 77.9% from 123 flights
Over the most recent 12 months (2025-08 to 2026-07), on-time arrivals averaged 79.1% against 78.8% in the 12 months before — broadly unchanged.
Data and methodology
Calculated by FlyerIntel from 2,717 STL → SEA flight records from the US DOT Bureau of Transportation Statistics, covering July 2023 – July 2026. Late means 15 or more minutes past scheduled arrival; cancelled and diverted flights are left out of on-time rates.
Full methodology · Data sources · Report a problem
Related research: How Long a Layover Needs to Be · Two Airlines on One Route · Best Time of Day to Fly From Major US Airports
Analysis last recomputed