STL (St. Louis) to SEA (Seattle) flights arrive on time 80% of the time. The most reliable airline on this route is Alaska Airlines at 84%. The average delay is 53 minutes. Delays on this route are most often caused by the airline (crew, maintenance, or boarding).
Source: Bureau of Transportation Statistics. Updated May 2026.STL → SEA
STL (St. Louis) to SEA (Seattle)
STL → SEA on-time performance by month
24
25
JanFebMarAprMayJunJulAugSepOctNovDec
Worse
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This route is on time most of the time. About 80% of flights arrive on schedule.
Delays on this route are most often caused by the airline (crew, maintenance, or boarding).
Accurate?
Alaska Airlines is significantly more reliable on this route at 84% on time vs Southwest Airlines at 66%.
Airline Comparison
Alaska Airlines leads at 84% on time; Southwest Airlines trails at 66%.
Accurate?
Good to know
Departing from STL
81% on timeTSA is currently ~24 min. Best time: 4 AM (about 5 min).
Arriving at SEA
82% on timeWhen flights into SEA are late, the average delay is 57 minutes. Build buffer if you have ground plans.
If connecting at SEA: TSA is ~15 min right now. Allow at least 60 minutes for a domestic connection.
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Data last updated May 2026. Source: Bureau of Transportation Statistics.