Carrier route record
ASONT→SEA
Alaska Airlines · Ontario to Seattle
- Flights
- 1,268
- Period
- July 2025 to June 2026
- Share of route
- 50%
- Carriers
- 4
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Alaska Airlines.
Alaska on ONT to SEA lands a B, 4 points better than the national rate of 77.6%. Roughly one flight in five arrives 15 minutes late or worse, and those flights are late by roughly 50 minutes on average. That is a workable record, not a spotless one. That rests on 1,268 flights, with a median arrival 4 minutes early.
Set against the rest of the country, Alaska's ONT to SEA record is 4 points better than the US average of 77.6%. That gap is worth roughly 41 fewer late arrivals for every thousand flights.
Key figures
On time
81.7%
Arrivals under 15 minutes late, of 1,238 completed flights
Avg delay
52 min
Across delayed arrivals only, not all flights
Cancelled
2.37%
National rate is 1.81%
Whole route
86.4%
Every carrier on ONT to SEA, 2,551 flights
These figures cover 1,268 flights between July 2025 and June 2026. The median arrival is 4 minutes early, which is the part an average hides: most flights here are fine, and the on-time rate is decided by a tail of badly late ones. On-time means under 15 minutes late, the DOT's own threshold.
Carrier by carrier
Alaska against every carrier on ONT to SEA
Alaska flew 1,268 of the 2,551 flights on ONT to SEA, about 50% of it. Its 81.7% on time is 5 points worse than the route as a whole, which runs 86.4%. Ranked by on-time rate it is last of four carriers on the route, where the range runs from Delta at 93.1% to Alaska at 81.7%. Two of those carriers flew fewer than 365 flights here, so treat their positions as rough.
Only one carrier clears this site's 365-flight floor here, so there is no comparison to draw. The table below is the full picture.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Delta Air Linesthin sample | 29 | 93.1% | 43 min | 0.00% | A+ |
| SkyWest Airlines | 1,085 | 92.1% | 83 min | 0.28% | A+ |
| Frontier Airlinesthin sample | 169 | 82.8% | 96 min | 0.00% | B+ |
| Alaska Airlines (this page) | 1,268 | 81.7% | 52 min | 2.37% | B |
Departure window
When Alaska runs best on this route
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 33 points, against half a point between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am350 flights92.8%
- 8am–11am84 flights90.5%
- 11am–2pm270 flights84.1%
- 2pm–5pm335 flights78.4%
- 5pm–8pm204 flights59.9%
- 8pm–5am25 flights—
Scale runs 50% to 100%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 59.9% on time, against 92.8% for the 5am–8am slot. By evening the aircraft flying these rotations have absorbed a full day of small delays and there is no slack left to recover in. The 5am–8am window is the busiest, with 350 flights scheduled in it.
Across the year
Alaska on ONT to SEA through the year
July is the worst month at 72.9% on time, 22 points below February, the best at 94.9%. Summer afternoon convection and peak-season schedules land on the same weeks every year, so this is a pattern you can book around rather than a run of bad luck. July was the busiest month here, with 149 flights.
Across the week, Tuesday is the strongest day at 84.6% on time and Thursday the weakest at 77.2%. 7 points is a smaller lever than departure hour, but it is free.
Delay causes
Why Alaska runs late on this route
One category carries most of the weight here. Late-arriving aircraft accounts for 50% of the 12,000 delay minutes carriers reported, and the remaining four split what is left. The split is by minutes rather than by flights, so a few very long delays count for as much as many short ones.
- 50%Late-arriving aircraft
- 29%Carrier
- 20%National Airspace System
- 1%Extreme weather
- 0%Security
50% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. That is a cascade, and cascades start small and grow through the day. Across 12,000 reported delay minutes here, that single category outweighs weather by 50 to one. It is the strongest argument for booking the first departure of the morning, when the aircraft has been sitting at the gate overnight with nothing to inherit. The split is drawn from 11,722 reported delay minutes.
The practical consequence: the 5am–8am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 92.8% on time here.
Cancellations sit at 2.37% against a national 1.81%, which is ordinary. Diversions add another 0.00%.
Connections and stage length
What a delay here costs
Badly late arrivals are rare here: only 4.3% land an hour or more behind schedule, against 8.1% nationally. Connections built on this flight are about as safe as US domestic connections get, though a cancelled flight still ignores every layover you give it.
The 956 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. It is also long enough that the aircraft usually flies three or four legs a day rather than six, which slows how fast delay compounds.
The return leg is a different operation and performs like one: it runs 77.4% on time across 1,268 flights, 4 points below this direction. Departure banks, aircraft rotations and the congestion at each end all differ, so scoring the two directions together would average away a real 4 points of difference.
The sample behind these figures is 1,268 flights, enough that the headline rate is stable to within roughly a point. The hour-block and month splits divide that further, so read the thinner bars with more caution than the headline.
What to do with this
Booking Alaska on ONT to SEA
Put together: the calendar is the biggest lever here, not the carrier or the hour. February runs 94.9% on time and July 72.9%, a swing of 22 points. If the dates move at all, move them out of July before you think about anything else. 1,238 completed flights over 12 months sit behind that.
Related
Where to go next
- ONT to SEA, every carrier
- Alaska on SEA to ONT, the return leg
- SkyWest Airlines on ONT to SEA92.1%
- Frontier Airlines on ONT to SEA82.8%
- Alaska Airlines network-wide record
- Seattle-Tacoma International (SEA) delay statistics
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.04 million flight records
Source: US DOT Bureau of Transportation Statistics, on-time performance data, July 2025 to June 2026. Last updated 15 September 2026; recomputed monthly. How this data is collected.