Carrier route record

ASSEA→ONT

Alaska Airlines · Seattle to Ontario

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 SEA to ONT lands a B, level with the national rate of 77.6%. Roughly one flight in four arrives 15 minutes late or worse, and those flights are late by roughly 45 minutes on average. That is a workable record, not a spotless one. That rests on 1,268 flights, with a median arrival 3 minutes early.

The US average over the same twelve months is 77.6%, so there is little to separate Alaska on SEA to ONT from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.

On time

77.4%

Arrivals under 15 minutes late, of 1,242 completed flights

Avg delay

47 min

Across delayed arrivals only, not all flights

Cancelled

2.05%

National rate is 1.81%

Whole route

82.9%

Every carrier on SEA to ONT, 2,550 flights

These figures cover 1,268 flights between July 2025 and June 2026. The median arrival is 3 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 SEA to ONT

Alaska flew 1,268 of the 2,550 flights on SEA to ONT, about 50% of it. Its 77.4% on time is 6 points worse than the route as a whole, which runs 82.9%. 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 77.4%. 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.

On-time performance by carrier on SEA to ONT
Airline	Flights	On time	Avg delay	Cancelled	Grade
Delta Air Linesthin sample	29	93.1%	32 min	0.00%	A+
SkyWest Airlines	1,084	89.7%	52 min	0.37%	A+
Frontier Airlinesthin sample	169	78.4%	77 min	1.18%	B
Alaska Airlines (this page)	1,268	77.4%	47 min	2.05%	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 21 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–8am87 flights89.5%
8am–11am317 flights85.2%
11am–2pm270 flights78.6%
2pm–5pm237 flights68.8%
5pm–8pm57 flights87.7%
8pm–5am300 flights69.8%

Scale runs 60% to 95%. Rows with fewer than 30 flights show a dash.

Book the early departure. Flights leaving between 5am–8am arrive on time 89.5% of the time, against 68.8% for the afternoon window. That is 21 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 8am–11am window is the busiest, with 317 flights scheduled in it.

Across the year

Alaska on SEA to ONT through the year

Darker means more delays. Figures are on-time percentages.September best, July worst

July is the worst month at 62.9% on time, 26 points below September, the best at 88.6%. 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, Saturday is the strongest day at 82.8% on time and Friday the weakest at 72.7%. 10 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 43% of the 13,000 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.

Late-arriving aircraft
43%
Carrier
41%
National Airspace System
15%
Security
1%
Extreme weather
1%

43% 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 13,000 reported delay minutes here, that single category outweighs weather by 43 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 13,083 reported delay minutes.

The largest share of delay minutes, 41%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. Unlike weather, that is a management outcome, and it is the category where the gap between two carriers on the same schedule is genuinely earned. It accounts for 5,381 of the 13,000 delay minutes reported here.

Cancellations sit at 2.05% against a national 1.81%, which is ordinary. Diversions add another 0.00%.

Connections and stage length

What a delay here costs

5.1% of arrivals land an hour or more late, close to the national 8.1%. That is the figure that decides a connection, and it says a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route last roughly 45 minutes, which a normal layover absorbs.

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 81.7% on time across 1,268 flights, 4 points above 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 SEA to ONT

Put together: the calendar is the biggest lever here, not the carrier or the hour. September runs 88.6% on time and July 62.9%, a swing of 26 points. If the dates move at all, move them out of July before you think about anything else. 1,242 completed flights over 12 months sit behind that.

Where to go next

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.

Key figures