ONT (Ontario) to SEA (Seattle) flights arrive on time 87% of the time. The most reliable airline on this route is Delta Air Lines at 95%. The average delay is 66 minutes. Delays on this route are most often caused by the airline (crew, maintenance, or boarding).
Source: Bureau of Transportation Statistics. Updated August 2026.ONT → SEA
ONT (Ontario) to SEA (Seattle)
ONT → SEA on-time performance by month
24
25
26
JanFebMarAprMayJunJulAugSepOctNovDec
Worse
Better
This route is usually on time. About 87% of flights arrive on schedule.
Delays on this route are most often caused by the airline (crew, maintenance, or boarding).
Accurate?
Delta Air Lines edges out Alaska Airlines on this route — 95% vs 83% on time.
Airline Comparison
Delta Air Lines leads at 95% on time; Alaska Airlines trails at 83%.
Accurate?
Good to know
Departing from ONT
82% on timeTSA is currently ~12 min. Best time: 4 AM (about 5 min).
Arriving at SEA
80% 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 ~22 min right now. Allow at least 60 minutes for a domestic connection.
Flight cancelled or delayed?
Check what Delta Air Lines owes you — refund rights, action plan, complaint email. Free.
Flying out of ONT? We'll brief you.
Delays, TSA, weather, gates — we'll let you know if something matters.
Know someone flying soon?
Send them the link — delay data, TSA waits, weather, all free.
Data last updated August 2026. Source: Bureau of Transportation Statistics.