Route profile
SEA→ONT
Flight reliability, delays and best times to fly from Seattle to Ontario, 956 miles.
Right now
Aviation weather is not currently a factor.
Aviation weather is not currently a factor.
Route reliability
July 2023 – July 2026
Better than 82% of comparable major US routes (4,598 compared)
Calculated from 7,756 flights. How this is calculated
SEA → ONT arrives on time 81.8% of the time; the return trip, ONT → SEA, arrives on time 86.3% of the time, a 4.4-point gap between the two directions of the same city pair.
SEA → ONT spends 27.2 minutes on the ground on a 956-mile trip: 22.3 minutes from pushback to wheels-up at SEA and 4.9 minutes from touchdown to gate at ONT.
Source: US DOT Bureau of Transportation Statistics · Data covering July 2023 – July 2026
What stands out
This route has stayed remarkably steady year over year, a smaller swing than 95% of 5,368 comparable routes.
82.6% on time over the most recent 12 months (2025-08 to 2026-07), against 82.3% in the 12 months before (2024-08 to 2025-07), virtually unchanged.
Source: FlyerIntel analysis of US DOT BTS data · July 2023 – July 2026 · Ranked against every other route with the same kind of figure and at least 5,368 in the comparison.
What sets this route apart
Where SEA to ONT differs most from similar routes by hour, weekday, month and airline, July 2023 – July 2026.
SEA to ONT is at its best against routes of similar length for flights scheduled at 7 PM: 85.9% arrive on time, 19.2 points ahead of the 66.7% those routes manage at that hour. Against all other routes the gap is 18.1 points.
SEA to ONT struggles most at 1 PM: 70.0% of its flights scheduled then arrive on time, 6.3 points behind the 76.3% on routes of similar length at the same hour. Against all other routes the gap is 7.1 points.
SEA to ONT holds up on Saturdays better than routes of similar length do: 84.7% on time to their 77.9%, a 6.8 points lead. Against all other routes the gap is 5.6 points.
May is kinder to SEA to ONT than to routes of similar length: 84.8% on time against 74.5%, 10.3 points better. Against all other routes the gap is 9.6 points.
SkyWest Airlines does better on SEA to ONT than on its routes of similar length: 89.2% on time here, 83.5% there, 5.7 points apart. Against all other routes the gap is 8 points.
SEA to ONT against comparable routes
July 2023 – July 2026| Measure | This route | Compared with | Them | Gap | Flights behind it |
|---|---|---|---|---|---|
| Hour: 7 PM departures | 85.9% | routes of similar length | 66.7% | +19.2 pts | 975 here, 197,236 there |
| Hour: 1 PM departures | 70.0% | routes of similar length | 76.3% | −6.3 pts | 360 here, 177,896 there |
| Weekday: Saturday | 84.7% | routes of similar length | 77.9% | +6.8 pts | 976 here, 405,682 there |
| Month: May | 84.8% | routes of similar length | 74.5% | +10.3 pts | 757 here, 255,316 there |
| Airline: SkyWest Airlines | 89.2% | routes of similar length | 83.5% | +5.7 pts | 2,882 here, 57,058 there |
Each comparison pools the flights of other routes, with this route’s own left out. Similar length means within 15% of this route’s 956 miles, with at least 5 such routes. A bucket is set against the most comparable group that has enough flights: similar length, then the same origin (at least 3 routes), then all other routes. Hours, weekdays and months appear only where both sides have 120 completed flights, and airlines where both have 600. The gap must be at least 2 points and 2 standard errors, and only the largest gap each way is kept per measure. These are differences in the flights counted, not causes.
Why SEA → ONT flights are cancelled
July 2023 – July 2026
SEA → ONT cancelled 80 of 7,756 scheduled flights — about 1 in every 97. The reason filed most often was the airline, 73.8% of the cancellations coded on this route — about 1 in every 131 scheduled flights.
Share of cancellations
Of 80 cancelled departures carrying a reason code.
What each reason means
Crew, maintenance, aircraft cleaning, baggage or fueling: what BTS counts as within the carrier’s own control.
59 cancellations, 73.8% of the total.
Conditions the carrier judged severe enough to stop the flight: a blizzard, a hurricane, a line of thunderstorms.
14 cancellations, 17.5% of the total.
Airport capacity, air traffic control flow programs, heavy traffic and ordinary bad weather. A system decision, not the airline’s.
7 cancellations, 8.8% of the total.
A terminal evacuation, a security breach, screening equipment failure, or screening queues over 29 minutes.
0 cancellations, 0.0% of the total.
Reason codes are the operating airline’s own filing with US DOT, not an independent finding of fault. Ordinary bad weather is filed under air traffic, so weather’s full share is larger than its bar.
80 coded cancellations were recorded on SEA → ONT; the section appears from 50.
When it goes wrong
July 2023 – July 2026
30 min late
against a median of 5 min early
Percentiles over 7,756 operations; cancelled and diverted flights are counted separately.
Will your connection be tight enough?
Layovers at ONT after arriving from SEA.
| Connection time | Chance of missing | Reads as |
|---|---|---|
| 30 min | 37% | Likely to miss |
| 45 min | 17% | High risk |
| 60 min | 9.7% | Some risk |
| 90 min | 4.1% | Low risk |
| 120 min | 2.1% | Low risk |
This is one leg of a connection. Gate changes and the next flight's own schedule matter too. And a connection can fail before delay is even the question — this route cancels 1.03% of the time and diverts 0.15% of the time, which a late arrival never shows up in.
Chance of missing is the share of 7,664 arrivals on this route that landed later than the connection time less 30 minutes to reach the next gate.
The worst tenth of arrivals on this route land at least 30 minutes late (90th-percentile gate arrival delay), over 7,756 operations.
Any other layover length: connection checker.
Best time to fly
SEA → ONT flights departing 5–9 AM arrived on time 90.3% of the time, against 66.5% for 9 PM–5 AM departures, a gap of 23.8 percentage points.
By departure window
By departure hour
- 12 AM to 5 AM: too few flights to score
- 6 AM: 91.9% on time from 433 flights
- 7 AM: 89.2% on time from 543 flights
- 8 AM: 90.1% on time from 873 flights
- 9 AM: too few flights to score
- 10 AM: 82.7% on time from 350 flights
- 11 AM: 87.4% on time from 441 flights
- 12 PM: 75.5% on time from 666 flights
- 1 PM: 70.0% on time from 366 flights
- 2 PM: 88.2% on time from 554 flights
- 3 PM: 77.9% on time from 689 flights
- 4 PM: 83.1% on time from 237 flights
- 5 PM: 70.5% on time from 354 flights
- 6 PM: too few flights to score
- 7 PM: 85.9% on time from 987 flights
- 8 PM: 76.2% on time from 423 flights
- 9 PM: 66.5% on time from 633 flights
- 10 PM to 11 PM: too few flights to score
Why SEA → ONT runs late
July 2023 – July 2026
crew, maintenance, boarding and fueling, all within the carrier’s control
the inbound aircraft was late, so this flight started late
airspace and airport capacity, including weather-driven flow control
weather severe enough to stop this flight specifically
screening or terminal security incidents
Share of the delay minutes US DOT attributed to each cause for SEA → ONT. Only delays of 15 minutes or more are attributed.
Airlines on this route
Carriers with at least 200 flights, by the airline that operated each one.
| Carrier | Flights | On time | Cancelled | Median delay | Severe |
|---|---|---|---|---|---|
| Alaska Airlines | 3,858 | 76.3% | 1.53% | -1 min | 4.6% |
| SkyWest Airlines | 2,890 | 89.2% | 0.14% | -8 min | 2.4% |
| Delta Air Lines | 514 | 85.1% | 0.97% | -11 min | 6.5% |
| Frontier Airlines | 494 | 77.8% | 2.43% | -5 min | 8.5% |
Alaska Airlines flew 49.7% of the 7,756 flights listed. Frontier Airlines cancelled 2.43% of its flights here against 0.14% for SkyWest Airlines.
SkyWest Airlines arrived on time 12.9 percentage points more often than Alaska Airlines on this route.
Other ways to fly Seattle to Los Angeles
Airport pairs in the same two city markets, as the DOT defines them.
SEA → SNA is the most reliable pairing for this journey at 85.3% on time, against 81.8% for SEA → ONT.
Flights on this route
Flight numbers with at least 600 operations here and still on the schedule.
| Flight | Scheduled | Operations | On time |
|---|---|---|---|
| OO4031 SkyWest Airlines | 2:30 PM | 718 | 88.3% |
Weekly and seasonal patterns
By day of week
Tuesday is historically the most reliable day and Thursday the least, a gap of 7.6 percentage points.
By month
- Jan: 83.9%
- Feb: 80.4%
- Mar: 83.9%
- Apr: 87.2%
- May: 84.8%
- Jun: 80.0%
- Jul: 74.7%
- Aug: 76.7%
- Sep: 86.0%
- Oct: 87.4%
- Nov: 82.5%
- Dec: 80.4%
July is historically the weakest month and October the strongest, a spread of 12.7 percentage points.
Reliability over time
July 2023 – July 2026
- July 2023: 76.2% from 216 flights
- August 2023: 70.0% from 215 flights
- September 2023: 85.2% from 210 flights
- October 2023: 84.2% from 204 flights
- November 2023: 76.8% from 194 flights
- December 2023: 84.0% from 169 flights
- January 2024: 82.0% from 143 flights
- February 2024: 84.1% from 133 flights
- March 2024: 80.9% from 152 flights
- April 2024: 82.0% from 200 flights
- May 2024: 83.1% from 254 flights
- June 2024: 79.1% from 270 flights
- July 2024: 82.4% from 276 flights
- August 2024: 81.4% from 256 flights
- September 2024: 82.0% from 224 flights
- October 2024: 90.0% from 209 flights
- November 2024: 87.1% from 226 flights
- December 2024: 86.1% from 175 flights
- January 2025: 84.2% from 167 flights
- February 2025: 73.0% from 147 flights
- March 2025: 84.2% from 183 flights
- April 2025: 90.1% from 202 flights
- May 2025: 85.2% from 258 flights
- June 2025: 75.8% from 267 flights
- July 2025: 72.3% from 302 flights
- August 2025: 77.7% from 266 flights
- September 2025: 91.1% from 213 flights
- October 2025: 87.9% from 200 flights
- November 2025: 82.8% from 211 flights
- December 2025: 72.2% from 200 flights
- January 2026: 85.3% from 157 flights
- February 2026: 84.4% from 135 flights
- March 2026: 86.2% from 177 flights
- April 2026: 89.5% from 200 flights
- May 2026: 86.2% from 249 flights
- June 2026: 85.6% from 240 flights
- July 2026: 67.9% from 256 flights
Over the most recent 12 months (2025-08 to 2026-07), on-time arrivals averaged 82.6% against 82.3% in the 12 months before — broadly unchanged.
Data and methodology
Calculated by FlyerIntel from 7,756 SEA → ONT flight records from the US DOT Bureau of Transportation Statistics, covering July 2023 – July 2026. Late means 15 or more minutes past scheduled arrival; cancelled and diverted flights are left out of on-time rates.
Full methodology · Data sources · Report a problem
Related research: How Long a Layover Needs to Be · Two Airlines on One Route · Best Time of Day to Fly From Major US Airports
Analysis last recomputed