Carrier route record

OOONT→SEA

SkyWest Airlines · Ontario to Seattle

Flights: 1,085
Period: July 2025 to June 2026
Share of route: 43%
Carriers: 4

Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with SkyWest Airlines.

SkyWest on ONT to SEA earns an A+. Close to nine flights in ten arrive inside the 15-minute window the DOT uses to define an on-time arrival, which puts it 15 points better than the national rate of 77.6%. When something does go wrong the average delay runs an hour and a half. That rests on 1,085 flights, with a median arrival 11 minutes early.

Set against the rest of the country, SkyWest's ONT to SEA record is 15 points better than the US average of 77.6%. That gap is worth roughly 145 fewer late arrivals for every thousand flights.

On time

92.1%

Arrivals under 15 minutes late, of 1,080 completed flights

Avg delay

83 min

Across delayed arrivals only, not all flights

Cancelled

0.28%

National rate is 1.81%

Whole route

86.4%

Every carrier on ONT to SEA, 2,551 flights

These figures cover 1,085 flights between July 2025 and June 2026. The median arrival is 11 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

SkyWest against every carrier on ONT to SEA

SkyWest flew 1,085 of the 2,551 flights on ONT to SEA, about 43% of it. Its 92.1% on time is 6 points better than the route as a whole, which runs 86.4%. Ranked by on-time rate it is number two 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.

On-time performance by carrier on ONT to SEA
Airline	Flights	On time	Avg delay	Cancelled	Grade
Delta Air Linesthin sample	29	93.1%	43 min	0.00%	A+
SkyWest Airlines (this page)	1,085	92.1%	83 min	0.28%	A+
Frontier Airlinesthin sample	169	82.8%	96 min	0.00%	B+
Alaska Airlines	1,268	81.7%	52 min	2.37%	B

Flight by flight

SkyWest flight numbers on ONT to SEA

Departure window

When SkyWest runs best on this route

Departure time is the single lever a traveller controls, and it moves the odds more than most people expect. Each bar below is the on-time rate for flights scheduled to leave inside that window, across 1,085 flights.

5am–8am365 flights95.0%
8am–11am1 flights—
11am–2pm293 flights93.8%
2pm–5pm133 flights90.2%
5pm–8pm293 flights88.0%
8pm–5am—

Scale runs 80% to 100%. Rows with fewer than 30 flights show a dash.

The early departures do better, though not dramatically: 95.0% on time for the 5am–8am window against 88.0% for 5pm–8pm. Worth taking if the schedule allows, not worth an extra connection. The 5am–8am window is the busiest, with 365 flights scheduled in it.

Across the year

SkyWest on ONT to SEA through the year

Darker means more delays. Figures are on-time percentages.February best, August worst

August is the worst month at 85.4% on time, 11 points below February, the best at 96.4%. 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. May was the busiest month here, with 124 flights.

The day of the week is close to irrelevant here: 3 points separates the best day from the worst. Weekly demand peaks are not what drives the delays on this operation.

Delay causes

Why SkyWest runs late on this route

One category carries most of the weight here. Carrier accounts for 73% of the 7,084 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.

Carrier
73%
Extreme weather
15%
National Airspace System
11%

Extreme weather accounts for 15% of delay minutes, well above the single-digit share typical across the system. Weather delays are lumpy: they arrive as whole bad days rather than as a steady drag, so the monthly strip above is the more useful view of the risk. The national share is 6%, so this operation carries roughly 2.4 times the usual weather exposure. The split is drawn from 7,084 reported delay minutes.

The largest share of delay minutes, 73%, 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 5,198 of the 7,084 delay minutes reported here.

Cancellations are rare at 0.28%, below the national 1.81% 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 stage length

What a delay here costs

Badly late arrivals are rare here: only 2.3% 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 runs 89.7% on time across 1,084 flights, within 2 points of this direction. The two legs are scored separately because they usually differ; on this city pair they happen not to.

One caution: this is a thin sample. 1,085 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.

What to do with this

Booking SkyWest on ONT to SEA

Put together: treat all of this as provisional. 1,085 flights over twelve months is enough to clear this site's floor and not enough to be confident to better than a couple of points. The 92.1% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 1,080 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