About 1 in 3 DL 3991 flights from San Francisco arrived 15+ minutes late, diverted or cancelled over the past year (36%); 0.7% were cancelled. The typical flight landed 4 minutes late.
DL 3991: SFO → SEA
Scheduled to leave San Francisco at 8:59 p.m. local time, operated by SkyWest as OO 3991. Over the past year it arrived on time 64% of the time (296 flights), in line with other DL flights on the route at that hour (64%). Last seen in the data Aug 31, 2026.
Usually Delta Air Lines's last flight of the day from San Francisco to Seattle (100% of days). Delta Air Lines's last SFO–SEA flight was cancelled 0.5% of the time, against 1.8% for its earlier ones. If it's cancelled, the next Delta Air Lines flight is usually around 5:55 a.m. the next morning.
Month by month
By day of week
| Day | Flights | On time |
|---|---|---|
| Monday | 46 | 52% |
| Tuesday | 43 | 77% |
| Wednesday | 43 | 67% |
| Thursday | 42 | 48% |
| Friday | 41 | 56% |
| Saturday | 37 | 81% |
| Sunday | 44 | 68% |
Why it was late
All flights SFO → SEA · Connecting off DL 3991? Check the risk
DL 3991: SEA → SFO
Scheduled to leave Seattle at 4:40 p.m. local time, operated by SkyWest as OO 3991. Over the past year it arrived on time 59% of the time (296 flights), in line with other DL flights on the route at that hour (57%). Last seen in the data Aug 31, 2026.
Month by month
By day of week
| Day | Flights | On time |
|---|---|---|
| Monday | 46 | 57% |
| Tuesday | 43 | 72% |
| Wednesday | 43 | 65% |
| Thursday | 42 | 60% |
| Friday | 41 | 46% |
| Saturday | 37 | 70% |
| Sunday | 44 | 48% |
Why it was late
All flights SEA → SFO · Connecting off DL 3991? Check the risk
Questions
How often is DL 3991 from SFO to SEA late?
Delta Air Lines 3991 from San Francisco, CA to Seattle, WA arrived 15 or more minutes late, was diverted or was cancelled on 36% of 296 scheduled flights between September 2025 and August 2026. 0.7% were cancelled.
How often is DL 3991 from SEA to SFO late?
Delta Air Lines 3991 from Seattle, WA to San Francisco, CA arrived 15 or more minutes late, was diverted or was cancelled on 41% of 296 scheduled flights between September 2025 and August 2026. 0.7% 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.