About 1 in 7 DL 4031 flights from Seattle arrived 15+ minutes late, diverted or cancelled over the past year (14%); 0.3% were cancelled. The typical flight landed 7 minutes early.
DL 4031: SEA → ONT
Scheduled to leave Seattle at 2:30 p.m. local time, operated by SkyWest as OO 4031. Over the past year it arrived on time 86% of the time (348 flights), in line with other DL flights on the route at that hour (85%). Last seen in the data Aug 31, 2026.
Month by month
By day of week
| Day | Flights | On time |
|---|---|---|
| Monday | 51 | 88% |
| Tuesday | 50 | 84% |
| Wednesday | 50 | 86% |
| Thursday | 50 | 82% |
| Friday | 50 | 90% |
| Saturday | 48 | 88% |
| Sunday | 49 | 88% |
Why it was late
All flights SEA → ONT · Connecting off DL 4031? Check the risk
DL 4031: ONT → SEA
Scheduled to leave Ontario at 5:50 p.m. local time, operated by SkyWest as OO 4031. Over the past year it arrived on time 88% of the time (322 flights), in line with other DL flights on the route at that hour (88%). Last seen in the data Aug 31, 2026.
Usually Delta Air Lines's last flight of the day from Ontario to Seattle (100% of days). Delta Air Lines's last ONT–SEA flight was cancelled 0.3% of the time, against 0.3% for its earlier ones. If it's cancelled, the next Delta Air Lines flight is usually around 6:20 a.m. the next morning.
Month by month
By day of week
| Day | Flights | On time |
|---|---|---|
| Monday | 48 | 88% |
| Tuesday | 47 | 85% |
| Wednesday | 47 | 89% |
| Thursday | 45 | 84% |
| Friday | 45 | 89% |
| Saturday | 44 | 93% |
| Sunday | 46 | 89% |
Why it was late
All flights ONT → SEA · Connecting off DL 4031? Check the risk
Questions
How often is DL 4031 from SEA to ONT late?
Delta Air Lines 4031 from Seattle, WA to Ontario, CA arrived 15 or more minutes late, was diverted or was cancelled on 14% of 348 scheduled flights between September 2025 and August 2026. 0.3% were cancelled.
How often is DL 4031 from ONT to SEA late?
Delta Air Lines 4031 from Ontario, CA to Seattle, WA arrived 15 or more minutes late, was diverted or was cancelled on 12% of 322 scheduled flights between September 2025 and August 2026. 0.3% were cancelled.
Flight numbers change. Figures cover flights with this airline, number and route only. "Likely range" is the 95% interval for the true on-time rate given the number of flights. This is history, not live status: check Delta Air Lines for today's flight. Method.