Route profile
ONT→SEA
Flight reliability, delays and best times to fly from Ontario to Seattle, 956 miles.
Right now
Aviation weather is not currently a factor.
Weather conditions are strongly associated with delays and cancellations.
Route reliability
July 2023 – July 2026
Better than 90% of comparable major US routes (4,598 compared)
Calculated from 7,752 flights. How this is calculated · What counts as on time
ONT → SEA arrives on time 86.3% of the time; the return trip, SEA → ONT, arrives on time 81.8% of the time, a 4.4-point gap between the two directions of the same city pair.
ONT → SEA spends 28.1 minutes on the ground on a 956-mile trip: 15.5 minutes from pushback to wheels-up at ONT and 12.6 minutes from touchdown to gate at SEA.
Source: US DOT Bureau of Transportation Statistics · Data covering July 2023 – July 2026
What stands out
Every day of the week performs about the same on this route, steadier than 99% of 4,467 comparable routes.
87.7% on time on the best day (Saturday) against 84.6% on the worst (Friday).
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 4,467 in the comparison.
What sets this route apart
Where ONT to SEA differs most from similar routes by hour, weekday, month and airline, July 2023 – July 2026.
ONT to SEA is at its best against routes of similar length for flights scheduled at 3 PM: 91.4% arrive on time, 21 points ahead of the 70.4% those routes manage at that hour. Against all other routes the gap is 18.7 points.
ONT to SEA holds up on Sundays better than routes of similar length do: 86.0% on time to their 73.9%, a 12.1 points lead. Against all other routes the gap is 11.2 points.
July is kinder to ONT to SEA than to routes of similar length: 82.7% on time against 68.4%, 14.3 points better. Against all other routes the gap is 13 points.
SkyWest Airlines does better on ONT to SEA than on its routes of similar length: 91.1% on time here, 83.4% there, 7.7 points apart. Against all other routes the gap is 9.9 points.
ONT to SEA against comparable routes
July 2023 – July 2026| Measure | This route | Compared with | Them | Gap | Flights behind it |
|---|---|---|---|---|---|
| Hour: 3 PM departures | 91.4% | routes of similar length | 70.4% | +21.0 pts | 301 here, 185,147 there |
| Weekday: Sunday | 86.0% | routes of similar length | 73.9% | +12.1 pts | 1,173 here, 451,155 there |
| Month: July | 82.7% | routes of similar length | 68.4% | +14.3 pts | 1,033 here, 333,850 there |
| Airline: SkyWest Airlines | 91.1% | routes of similar length | 83.4% | +7.7 pts | 2,874 here, 57,066 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 ONT → SEA flights are cancelled
July 2023 – July 2026
ONT → SEA cancelled 77 of 7,752 scheduled flights — about 1 in every 101. The reason filed most often was the airline, 75.3% of the cancellations coded on this route — about 1 in every 134 scheduled flights.
Share of cancellations
Of 77 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.
58 cancellations, 75.3% of the total.
Conditions the carrier judged severe enough to stop the flight: a blizzard, a hurricane, a line of thunderstorms.
12 cancellations, 15.6% 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, 9.1% 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.
77 coded cancellations were recorded on ONT → SEA; the section appears from 50.
When it goes wrong
July 2023 – July 2026
22 min late
against a median of 8 min early
Percentiles over 7,752 operations; cancelled and diverted flights are counted separately.
Will your connection be tight enough?
Layovers at SEA after arriving from ONT.
| Connection time | Chance of missing | Reads as |
|---|---|---|
| 30 min | 31% | Likely to miss |
| 45 min | 13% | Some risk |
| 60 min | 7.6% | Some risk |
| 90 min | 3.7% | Low risk |
| 120 min | 2.4% | 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 0.99% of the time and diverts 0.17% of the time, which a late arrival never shows up in.
Chance of missing is the share of 7,662 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 22 minutes late (90th-percentile gate arrival delay), over 7,752 operations.
Any other layover length: connection checker.
Best time to fly
ONT → SEA flights departing 5–9 AM arrived on time 92.4% of the time, against 70.3% for 9 PM–5 AM departures, a gap of 22.1 percentage points.
By departure window
By departure hour
- 12 AM to 4 AM: too few flights to score
- 5 AM: 92.9% on time from 202 flights
- 6 AM: 92.7% on time from 1,734 flights
- 7 AM: 91.9% on time from 320 flights
- 8 AM to 9 AM: too few flights to score
- 10 AM: 88.1% on time from 678 flights
- 11 AM: 88.8% on time from 1,114 flights
- 12 PM: 84.5% on time from 235 flights
- 1 PM: too few flights to score
- 2 PM: 82.8% on time from 434 flights
- 3 PM: 91.4% on time from 301 flights
- 4 PM: 79.3% on time from 825 flights
- 5 PM: 88.2% on time from 564 flights
- 6 PM: 76.1% on time from 345 flights
- 7 PM: 75.6% on time from 450 flights
- 8 PM: 78.0% on time from 201 flights
- 9 PM: 70.3% on time from 145 flights
- 10 PM to 11 PM: too few flights to score
Why ONT → SEA 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 ONT → SEA. Only delays of 15 minutes or more are attributed. What the five causes mean
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 | 3,856 | 82.7% | 1.66% | -5 min | 4.2% |
| SkyWest Airlines | 2,890 | 91.1% | 0.17% | -10 min | 2.7% |
| Delta Air Lines | 513 | 89.6% | 0.58% | -14 min | 4.7% |
| Frontier Airlines | 493 | 82.6% | 1.01% | -10 min | 7.2% |
Alaska Airlines flew 49.7% of the 7,752 flights listed. Alaska Airlines cancelled 1.66% of its flights here against 0.17% for SkyWest Airlines.
SkyWest Airlines arrived on time 8.5 percentage points more often than Frontier Airlines on this route.
Other ways to fly Los Angeles to Seattle
Airport pairs in the same two city markets, as the DOT defines them.
Flying to SEA from the Los Angeles area? Compare ONT, LAX, SNA, BUR for SEA, with the same test for what counts as a real difference.
Weekly and seasonal patterns
By day of week
Saturday is historically the most reliable day and Friday the least, a gap of 3.1 percentage points.
By month
- Jan: 86.5%
- Feb: 89.3%
- Mar: 87.6%
- Apr: 91.5%
- May: 86.6%
- Jun: 83.5%
- Jul: 82.7%
- Aug: 83.4%
- Sep: 86.4%
- Oct: 90.5%
- Nov: 87.4%
- Dec: 84.9%
July is historically the weakest month and April the strongest, a spread of 8.8 percentage points.
Reliability over time
July 2023 – July 2026
- July 2023: 86.9% from 216 flights
- August 2023: 83.0% from 213 flights
- September 2023: 89.0% from 210 flights
- October 2023: 92.1% from 204 flights
- November 2023: 84.3% from 194 flights
- December 2023: 86.8% from 169 flights
- January 2024: 92.1% from 143 flights
- February 2024: 92.5% from 133 flights
- March 2024: 90.1% from 152 flights
- April 2024: 93.0% from 200 flights
- May 2024: 86.2% from 254 flights
- June 2024: 81.0% from 270 flights
- July 2024: 82.4% from 276 flights
- August 2024: 83.3% from 255 flights
- September 2024: 82.1% from 224 flights
- October 2024: 94.3% from 209 flights
- November 2024: 90.3% from 227 flights
- December 2024: 86.5% from 174 flights
- January 2025: 80.9% from 166 flights
- February 2025: 80.4% from 147 flights
- March 2025: 85.6% from 183 flights
- April 2025: 90.6% from 202 flights
- May 2025: 84.7% from 258 flights
- June 2025: 85.3% from 266 flights
- July 2025: 81.6% from 302 flights
- August 2025: 83.7% from 266 flights
- September 2025: 88.2% from 213 flights
- October 2025: 84.8% from 200 flights
- November 2025: 87.3% from 211 flights
- December 2025: 81.7% from 200 flights
- January 2026: 87.9% from 158 flights
- February 2026: 95.6% from 135 flights
- March 2026: 87.4% from 177 flights
- April 2026: 91.0% from 200 flights
- May 2026: 89.1% from 249 flights
- June 2026: 84.4% from 240 flights
- July 2026: 80.6% from 256 flights
Over the most recent 12 months (2025-08 to 2026-07), on-time arrivals averaged 86.3% against 85.5% in the 12 months before — broadly unchanged.
Data and methodology
Calculated by FlyerIntel from 7,752 ONT → SEA 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