Carrier performance at one airport
WN→ONT
Southwest Airlines at Ontario International
- Departures
- 11,660
- Period
- June 2025 to May 2026
- Routes
- 12
- Rank here
- #4 of 7
Southwest Airlines at Ontario lands a B+, 5 points better than the national rate of 77.4%. About one flight in six arrive 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 11,660 flights, of which Delta Air Lines flew 1,876 at 90.7% on time.
Measured against the airport rather than the country, Southwest Airlines runs half a point behind the 82.4% 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
82.1%
11,598 completed departures
Avg delay
52 min
Across delayed flights only
Cancelled
0.40%
At ONT, this carrier only
Rank here
#4
Of 7 carriers clearing the floor at ONT
These figures cover 12,000 flights between June 2025 and May 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 90.7% of the time; Frontier Airlines manages 75.8%. Sample sizes sit next to every figure, because a two-point gap across 2,204 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Delta Air Lines | 1,876 | 90.7% | 92 min | 1.49% | A |
| SkyWest Airlines | 1,734 | 90.1% | 80 min | 0.40% | A+ |
| Alaska Airlines | 1,969 | 84.6% | 56 min | 1.63% | B |
| Southwest Airlines (this page) | 11,660 | 82.1% | 52 min | 0.40% | B+ |
| American Airlines | 3,648 | 80.3% | 98 min | 1.92% | B |
| United Airlines | 2,559 | 79.4% | 73 min | 0.51% | B+ |
| Frontier Airlines | 2,204 | 75.8% | 81 min | 1.45% | 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 12 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 | 2,108 | 86.3% | 56 min | 0.24% | A+ |
| ONT to LAS · Las Vegas | 1,763 | 77.5% | 55 min | 0.74% | B+ |
| ONT to PHX · Phoenix | 1,608 | 82.6% | 49 min | 0.37% | B+ |
| ONT to OAK · Oakland | 1,514 | 86.7% | 59 min | 0.40% | A+ |
| ONT to SJC · San Jose | 1,319 | 85.9% | 56 min | 0.08% | A+ |
| ONT to DEN · Denver | 1,269 | 76.2% | 54 min | 0.39% | B+ |
| ONT to DAL · Dallas | 408 | 78.0% | 40 min | 1.72% | B |
| ONT to HOU · Houstonthin sample | 362 | 67.6% | 47 min | 0.00% | C+ |
| ONT to MDW · Chicagothin sample | 360 | 90.2% | 42 min | 0.28% | A+ |
| ONT to BNA · Nashvillethin sample | 336 | 80.2% | 44 min | 0.30% | B+ |
| ONT to AUS · Austinthin sample | 336 | 77.8% | 40 min | 0.30% | B+ |
| ONT to BWI · Baltimorethin sample | 277 | 80.8% | 45 min | 0.36% | B+ |
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 24 points, against 15 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am2,676 flights94.3%
- 8am–11am2,365 flights89.4%
- 11am–2pm1,919 flights78.3%
- 2pm–5pm2,045 flights70.7%
- 5pm–8pm1,470 flights75.3%
- 8pm–5am1,185 flights74.2%
Scale runs 60% to 100%. Rows with fewer than 30 flights show a dash.
Book the early departure. Flights leaving between 5am–8am arrive on time 94.3% of the time, against 70.7% for the afternoon window. That is 24 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on.
Across the year
Seasonal pattern
Delays peak in May, when the on-time rate falls to 75.6%. January is the strongest month at 87.9%. Moving a flexible trip across that boundary buys 12 points.
Delay causes
What holds this operation up
- 54%Late-arriving aircraft
- 23%National Airspace System
- 22%Carrier
- 1%Extreme weather
- 0%Security
54% 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 108,000 reported delay minutes here, that single category outweighs weather by 54 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.
Cancellations are rare at 0.40%, below the national 1.80% 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 4.8% land an hour or more behind schedule, against 8.2% 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 11,660 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 May 75.6%, a swing of 12 points. If the dates move at all, move them out of May before you think about anything else.
Common questions
Southwest Airlines at ONT
How often is Southwest Airlines at ONT delayed?
About one flight in six arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 17.9% of the 11,660 flights in this analysis, against 22.6% nationally. Delayed flights are late by roughly 50 minutes on average.
Which airline is most reliable on Southwest Airlines at ONT?
Delta Air Lines leads at 90.7% on time across 1,876 flights. Frontier Airlines is at the other end on 75.8%, 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 94.3% on time. The 2pm–5pm window is the weakest at 70.7%, 24 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 May delays on Southwest Airlines at ONT?
May is the weakest month at 75.6% on time, compared with 87.9% in January. Across the year that is 12 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, June 2025 to May 2026. Updated monthly. How this data is collected.