Carrier performance at one airport
WN→ONT
Southwest Airlines at Ontario International
- Departures
- 11,643
- Period
- September 2025 to August 2026
- Routes
- 13
- Rank here
- #5 of 7
Southwest Airlines at Ontario lands a B+, 4 points better than the national rate of 77.3%. About one flight in five arrives 15 minutes late or worse, and those flights are late by about 50 minutes on average. That rests on 11,643 flights, of which Delta Air Lines flew 1,811 at 90.0% on time.
Measured against the airport rather than the country, Southwest Airlines runs about a point behind the 82.1% weighted average across all carriers at ONT. That is the comparison worth making: every operator here works the same runways, the same airspace and the same weather.
Key figures
On time
81.1%
11,583 completed departures
Avg delay
51 min
Across delayed flights only
Cancelled
0.42%
At ONT, this carrier only
Rank here
#5
Of 7 carriers clearing the floor at ONT
These figures cover 12,000 flights between September 2025 and August 2026. The median arrival is 6 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.
Against the competition
Every carrier at ONT, ranked
The choice of carrier is not cosmetic here. Delta Air Lines arrives on time 90.0% of the time; Frontier Airlines manages 75.2%. Sample sizes sit next to every figure, because a two-point gap across 2,284 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Delta Air Lines | 1,811 | 90.0% | 93 min | 1.49% | A |
| SkyWest Airlines | 1,771 | 87.4% | 78 min | 0.40% | A+ |
| Alaska Airlines | 2,098 | 84.5% | 54 min | 1.29% | B |
| American Airlines | 3,545 | 83.3% | 103 min | 1.83% | B |
| Southwest Airlines (this page) | 11,643 | 81.1% | 51 min | 0.42% | B+ |
| United Airlines | 2,429 | 79.3% | 71 min | 0.54% | B+ |
| Frontier Airlines | 2,284 | 75.2% | 75 min | 1.31% | B |
The spread between Delta and Frontier is 15 points, wide enough that it should decide the booking. On a hundred trips that is 15 more arrivals inside the on-time window.
Route by route
Where Southwest Airlines flies from ONT
Southwest Airlines operates 13 routes out of ONT with enough volume to report. Route records inside one carrier at one airport still spread widely, because a short shuttle and a transcontinental have very different exposure to a late inbound.
| Route | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| ONT to SMF · Sacramento | 2,119 | 85.1% | 52 min | 0.28% | A+ |
| ONT to LAS · Las Vegas | 1,744 | 76.6% | 51 min | 0.80% | B+ |
| ONT to PHX · Phoenix | 1,615 | 80.5% | 50 min | 0.37% | B+ |
| ONT to OAK · Oakland | 1,450 | 86.0% | 58 min | 0.55% | A+ |
| ONT to SJC · San Jose | 1,320 | 85.9% | 57 min | 0.08% | A+ |
| ONT to DEN · Denver | 1,269 | 76.4% | 55 min | 0.24% | B+ |
| ONT to DAL · Dallas | 395 | 76.6% | 46 min | 1.52% | B |
| ONT to HOU · Houstonthin sample | 363 | 63.1% | 44 min | 0.00% | D+ |
| ONT to MDW · Chicagothin sample | 360 | 90.8% | 39 min | 0.28% | A+ |
| ONT to AUS · Austinthin sample | 337 | 73.5% | 40 min | 0.30% | C+ |
| ONT to BNA · Nashvillethin sample | 336 | 76.2% | 41 min | 0.60% | B+ |
| ONT to BWI · Baltimorethin sample | 254 | 83.8% | 41 min | 0.39% | B+ |
| ONT to HNL · Honoluluthin sample | 81 | 95.1% | 29 min | 0.00% | A+ |
Departure window
Best time of day for this operation
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 27 points, against 15 points between the best and worst carrier.
- 5am–8am2,522 flights95.4%
- 8am–11am2,378 flights88.5%
- 11am–2pm2,011 flights76.2%
- 2pm–5pm2,104 flights68.3%
- 5pm–8pm1,375 flights74.8%
- 8pm–5am1,253 flights74.8%
Scale runs 60% to 100%.
Book the early departure. Flights leaving between 5am–8am arrive on time 95.4% of the time, against 68.3% for the afternoon window. That is 27 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 5am–8am window is the busiest, with 2,522 flights scheduled in it.
Across the year
Seasonal pattern
June is the worst month at 73.3% on time, 15 points below January, the best at 87.9%. 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 1,049 flights.
Delay causes
What holds this operation up
- 55%Late-arriving aircraft
- 23%Carrier
- 21%National Airspace System
- 0%Security
- 0%Extreme weather
55% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 110,000 reported delay minutes here, that single category outweighs weather by 55 to one. The split is drawn from 110,326 reported delay minutes.
Cancellations are rare at 0.42%, below the national 1.89% 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.
Badly late arrivals are rare here: only 4.7% land an hour or more behind schedule, against 8.3% 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 sample behind these figures is 11,643 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.
Put together: the calendar is the biggest lever here, not the carrier or the hour. January runs 87.9% on time and June 73.3%, a swing of 15 points. If the dates move at all, move them out of June before you think about anything else. 11,583 completed flights over 12 months sit behind that.
Common questions
Southwest Airlines at ONT
How often is Southwest Airlines at ONT delayed?
About one flight in five arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 18.9% of the 11,643 flights in this analysis, against 22.7% nationally. Delayed flights are late by about 50 minutes on average.
Which airline is most reliable on Southwest Airlines at ONT?
Delta Air Lines leads at 90.0% on time across 1,811 flights. Frontier Airlines is at the other end on 75.2%, a gap of 15 points. Sample size matters as much as the percentage: a rate built from a few hundred flights moves around far more than one built from ten thousand.
What time of day has the fewest delays on Southwest Airlines at ONT?
The 5am–8am departure window is the strongest at 95.4% on time. The 2pm–5pm window is the weakest at 68.3%, 27 points behind. Later departures inherit delays from earlier flights the same aircraft has already flown, which is why the curve slopes the way it does.
How bad are June delays on Southwest Airlines at ONT?
June is the weakest month at 73.3% on time, compared with 87.9% in January. Across the year that is 15 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.
Related
Where to go next
Source: US DOT Bureau of Transportation Statistics, on-time performance data, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.