Flight number record
OO 3991
SkyWest Airlines · Seattle to San Francisco
- Route
- SEA → SFO
- Departs
- 16:25
- Flights
- 296
- Period
- September 2025 to August 2026
Historical statistics for September 2025 to August 2026, not live status. For today’s OO 3991, check with SkyWest Airlines. SkyWest Airlines flies under contract for larger airlines, so a ticket for this flight may show a different airline code and number.
OO 3991 draws a D+. Roughly one flight in two arrives at least 15 minutes late, and the typical late arrival is about 50 minutes behind schedule. Build slack into anything you connect to. That rests on 296 flights, with a median arrival 4 minutes late.
The national on-time rate over the same period is 77.3%, so OO 3991 runs 17 points behind the country as a whole. Across a thousand flights that is about 174 extra late arrivals.
Key figures
On time
59.9%
Arrivals under 15 minutes late, of 294 completed flights
Avg delay
51 min
Across delayed arrivals only, not all flights
Cancelled
0.68%
National rate is 1.89%
1 hour+ late
9.9%
National rate is 8.3%
These figures cover 296 flights between September 2025 and August 2026. Beyond the headline rate, 9.9% of arrivals land a full hour or more behind schedule, against 8.3% nationally.
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Schedule
When OO 3991 flies
OO 3991 flies SEA to SFO without a single fixed slot. Its most common scheduled departure was 16:25, used on 39 of 296 flights, with 16:40 (39 flights) and 17:30 (31 flights) next.
- Departs 16:2539 flights13.2%
- Departs 16:4039 flights13.2%
- Departs 17:3031 flights10.5%
Scale runs 0% to 100%.
Share of scheduled departures at each local time. Times used on fewer than one flight in ten are not listed.
A 16:25 departure sits in the 2pm–5pm window. Across every US flight scheduled in that window the on-time rate is 71.9%, and OO 3991 runs 12 points worse at 59.9%. Midday slots inherit some of the morning's delays without yet carrying the full weight of the evening's.
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Against the route
OO 3991 next to SEA to SFO
Every carrier on SEA to SFO combined arrived on time 59.8% of the time across 6,817 flights, so OO 3991 is about level with it. SkyWest flew 1,039 flights on the same city pair under all its flight numbers, including this one, and those ran 69.9% on time. Across its whole network SkyWest Airlines managed 78.7%, which this flight trails by 19 points.
| Compared with | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| OO 3991thin sample | 296 | 59.9% | 51 min | 0.68% | D+ |
| All SkyWest Airlines on SEA–SFO | 1,039 | 69.9% | 52 min | 1.06% | C |
| All carriers on SEA–SFO | 6,817 | 59.8% | 57 min | 1.11% | D |
| SkyWest Airlines, whole network | 855,406 | 78.7% | 88 min | 1.79% | B |
Across the year
OO 3991 quarter by quarter
OO 3991 did not run the same all year. Its best quarter was Oct–Dec 2025 at 78.9% on time and its weakest Jul–Sep 2026 at 41.9%, a swing of 37 points on roughly 74 flights a quarter. The twelve-month rate averages over that, so if you are flying in a weak quarter the quarter's own figure is the better guide.
- Jul–Sep 202523 flights—
- Oct–Dec 202572 flights78.9%
- Jan–Mar 202648 flights78.7%
- Apr–Jun 202691 flights48.4%
- Jul–Sep 202662 flights41.9%
Scale runs 35% to 85%. Rows with fewer than 30 flights show a dash.
By weekday, OO 3991 did best on Tuesday at 72.1% on time and worst on Friday at 47.5%. Each day rests on about 42 flights, so a gap of 25 points is worth noticing but could still narrow in another year.
Arrival by arrival
How late OO 3991 runs when it is late
The 118 late arrivals split 46 under half an hour, 43 between 30 and 60 minutes, and 29 an hour or more.
- 15+ min early48 flights16.3%
- Within 15 min128 flights43.5%
- 15–29 min late46 flights15.6%
- 30–59 min late43 flights14.6%
- 1–2 hours late22 flights7.5%
- 2+ hours late7 flights2.4%
Scale runs 0% to 100%.
Share of 294 completed flights by arrival against schedule.
Time lost at the gate mostly stays lost. Of 83 departures that left 15 minutes late or more, only 3 made it up before arrival. In the other direction, 38 flights left on time yet arrived 15 minutes late or more, so that delay built up after pushback: in the air, in a holding pattern or on the ground at SFO.
The worst days
Worst days for OO 3991
The latest arrival of the period was on 15 June 2026, 4 hours 13 minutes behind schedule; most of its delay minutes were filed as carrier-caused (crew, maintenance, fuelling, baggage). The same cause led on four of the five worst days.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 15 June 2026 | 4 hours 13 minutes | Carrier |
| 21 July 2026 | 3 hours 38 minutes | Carrier |
| 22 April 2026 | 3 hours 8 minutes | Carrier |
| 28 May 2026 | 3 hours 1 minute | National Airspace System |
| 1 October 2025 | 2 hours 44 minutes | Carrier |
Delay causes
Why OO 3991 runs late
National Airspace System accounts for 49% of the 6,013 delay minutes carriers reported here, and the remaining four split what is left.
- 49%National Airspace System
- 40%Carrier
- 10%Extreme weather
- 0%Security
The largest share of delay minutes, 40%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 2,410 of the 6,013 delay minutes reported here. The split is drawn from 6,013 delay minutes reported on OO 3991.
Cancellations are rare at 0.68%, below the national 1.89% and low enough to earn the plus on the grade. Roughly one flight in 100 is called off; the risk here is arriving late, not not arriving.
Connections and routes
What a delay on this flight costs
9.9% of arrivals land a full hour or more behind schedule, against 8.3% nationally. Ninety minutes is the honest minimum for a connection here, and two hours if the onward flight is on a separate ticket.
The 679 miles between these two airports put this in the middle of the US network, around two and a half to three hours of block time. That is enough cruise to absorb a ten-minute late pushback and not enough to absorb thirty.
OO 3991 is not only a SEA to SFO flight. It also flew SFO to SEA (296 flights, 64.3% on time) often enough to be scored on its own. Airlines attach one number to several legs of an aircraft's day, and each leg keeps its own record here, so check which city pair is on your booking before reading a rate.
One caution: this is a thin sample. 296 flights over twelve months is enough to clear this site's floor but not enough to pin the rate down tightly, and a single bad week moves it by more than a point. Treat the grade as a rough reading.
| Also flown as | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| SFO to SEAthin sample | 296 | 64.3% | 47 min | 0.68% | D+ |
What to do with this
Booking OO 3991
For a booking, read OO 3991 as 59.9% on time with 0.68% cancelled over 296 flights. Those are rates from the past twelve months, not a forecast for any particular day.
Related
Where to go next
- SEA to SFO, every carrier and departure
- SFO to SEA, the return direction
- United Airlines 737 on the same route53.9%
- Delta Air Lines 1412 on the same route60.1%
- Delta Air Lines 2635 on the same route69.6%
- SkyWest Airlines 3707 on the same route68.5%
- Alaska Airlines 655 on the same route67.2%
- Alaska Airlines 725 on the same route50.5%
- Seattle-Tacoma International (SEA) delay statistics
- San Francisco International (SFO) delay statistics
- SkyWest Airlines on-time record
- Every SkyWest Airlines flight number with a record
- The most and least reliable flight numbers in the US
- How often a connection fails at the major US hubs
A flight number here means SkyWest Airlines’s own number as it reports to the DOT. How the figures are computed is on the methodology page.
Source: US DOT Bureau of Transportation Statistics, on-time performance data, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.