Carrier route record
F9ONT→SEA
Frontier Airlines · Ontario to Seattle
- Flights
- 169
- Period
- July 2025 to June 2026
- Share of route
- 7%
- Carriers
- 4
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Frontier Airlines.
Frontier on ONT to SEA lands a B+, 5 points better than the national rate of 77.6%. About one flight in six arrives 15 minutes late or worse, and those flights are late by an hour and a half on average. That is a workable record, not a spotless one. That rests on 169 flights. The strongest carrier on the route with a full sample, SkyWest Airlines, flew 1,085 at 92.1% on time.
Set against the rest of the country, Frontier's ONT to SEA record is 5 points better than the US average of 77.6%. That gap is worth roughly 52 fewer late arrivals for every thousand flights.
Key figures
On time
82.8%
Arrivals under 15 minutes late, of 169 completed flights
Avg delay
96 min
Across delayed arrivals only, not all flights
Cancelled
0.00%
National rate is 1.81%
Whole route
86.4%
Every carrier on ONT to SEA, 2,551 flights
These figures cover 169 flights between July 2025 and June 2026. The median arrival is 14 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
Frontier against every carrier on ONT to SEA
Frontier flew 169 of the 2,551 flights on ONT to SEA, about 7% of it. Its 82.8% on time is 4 points worse than the route as a whole, which runs 86.4%. Ranked by on-time rate it is number three of four carriers on the route, where the range runs from Delta at 93.1% to Alaska at 81.7%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.
The choice of carrier is not cosmetic here. SkyWest Airlines arrives on time 92.1% of the time; Alaska Airlines manages 81.7%. Sample sizes sit next to every figure, because a two-point gap across 1,268 flights means less than a ten-point one.
| 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 Airlines (this page)thin sample | 169 | 82.8% | 96 min | 0.00% | B+ |
| Alaska Airlines | 1,268 | 81.7% | 52 min | 2.37% | B |
SkyWest leads Alaska by 10 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.
Departure window
When Frontier 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 169 flights.
- 5am–8am—
- 8am–11am96 flights85.4%
- 11am–2pm—
- 2pm–5pm54 flights75.9%
- 5pm–8pm19 flights—
- 8pm–5am—
Scale runs 65% to 90%. Rows with fewer than 30 flights show a dash.
Book the morning departure. Flights leaving between 8am–11am arrive on time 85.4% of the time, against 75.9% for the afternoon window. That is 10 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 96 flights scheduled in it.
Across the year
Frontier on ONT to SEA through the year
- Jul–Sep 202580 flights88.8%
- Oct–Dec 202546 flights73.9%
- Jan–Mar 20266 flights—
- Apr–Jun 202637 flights78.4%
Scale runs 65% to 95%. Rows with fewer than 30 flights show a dash.
Monthly volumes are too low here to break the year into twelve reliable readings. What the twelve-month total says is 82.8% on time across 169 flights.
Frontier on ONT to SEA did not run the same all year. Its best quarter was Jul–Sep 2025 at 88.8% on time and its weakest Oct–Dec 2025 at 73.9%, a swing of 15 points on roughly 56 flights a quarter. The twelve-month rate averages over that, so if you are flying in a weak quarter the quarter's own figure is the better guide.
Across the week, Sunday is the strongest day at 88.2% on time and Monday the weakest at 74.2%. 14 points is a smaller lever than departure hour, but it is free.
Delay causes
Why Frontier runs late on this route
One category carries most of the weight here. Late-arriving aircraft accounts for 78% of the 2,772 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.
- 78%Late-arriving aircraft
- 13%Carrier
- 9%National Airspace System
78% 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 2,772 reported delay minutes here, that single category outweighs weather by 78 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 2,772 reported delay minutes.
The practical consequence: the 8am–11am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 85.4% on time here.
Cancellations are rare at 0.00%, below the national 1.81% and low enough to earn the plus on the grade. Almost no flights are called off; the risk here is arriving late, not not arriving.
Connections and stage length
What a delay here costs
6.5% 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 an hour and a half, 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 78.4% on time across 169 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.
One caution: this is a thin sample. 169 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 Frontier on ONT to SEA
Put together: treat all of this as provisional. 169 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 82.8% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 169 completed flights over 12 months sit behind that.
Related
Where to go next
- ONT to SEA, every carrier
- Frontier on SEA to ONT, the return leg
- SkyWest Airlines on ONT to SEA92.1%
- Alaska Airlines on ONT to SEA81.7%
- Frontier Airlines network-wide record
- Seattle-Tacoma International (SEA) delay statistics
- Same route, different airline: where the carrier you pick matters most
- Why the first flight of the morning is statistically safest
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.