Carrier route record
WNSTL→PHX
Southwest Airlines · St. Louis to Phoenix
- Flights
- 1,600
- Period
- July 2025 to June 2026
- Share of route
- 70%
- Carriers
- 5
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Southwest Airlines.
Southwest on STL to PHX sits in the middle of the pack with a C+. About seven flights in ten arrive on time by the DOT's definition, 5 points worse than the national rate of 77.6%. The late ones land roughly 50 minutes behind schedule. That rests on 1,600 flights, with a median arrival right on schedule.
The national on-time rate over the same period is 77.6%, so Southwest on STL to PHX runs 5 points behind the country as a whole. Across a thousand flights that is about 54 extra late arrivals.
Key figures
On time
72.2%
Arrivals under 15 minutes late, of 1,593 completed flights
Avg delay
51 min
Across delayed arrivals only, not all flights
Cancelled
0.31%
National rate is 1.81%
Whole route
75.3%
Every carrier on STL to PHX, 2,284 flights
These figures cover 1,600 flights between July 2025 and June 2026. On-time means an arrival less than 15 minutes after the scheduled gate time, the same threshold the Department of Transportation uses in its own reports. Cancelled and diverted flights are excluded from the on-time rate and counted separately, which is why the cancellation column matters on its own.
Carrier by carrier
Southwest against every carrier on STL to PHX
Southwest flew 1,600 of the 2,284 flights on STL to PHX, most of the route. Its 72.2% on time is 3 points worse than the route as a whole, which runs 75.3%. Ranked by on-time rate it is last of five carriers on the route, where the range runs from Envoy at 100.0% to Southwest at 72.2%. Three 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.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Envoy Airthin sample | 30 | 100.0% | — | 0.00% | A+ |
| SkyWest Airlinesthin sample | 53 | 83.0% | 93 min | 0.00% | B+ |
| Frontier Airlinesthin sample | 53 | 82.7% | 210 min | 1.89% | B |
| American Airlines | 548 | 81.7% | 172 min | 0.91% | B+ |
| Southwest Airlines (this page) | 1,600 | 72.2% | 51 min | 0.31% | C+ |
Departure window
When Southwest runs best on this route
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 41 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–8am351 flights92.9%
- 8am–11am233 flights87.9%
- 11am–2pm163 flights72.2%
- 2pm–5pm254 flights73.6%
- 5pm–8pm296 flights51.5%
- 8pm–5am303 flights55.0%
Scale runs 45% to 100%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 51.5% on time, against 92.9% for the 5am–8am slot. By evening the aircraft flying these rotations have absorbed a full day of small delays and there is no slack left to recover in. The 5am–8am window is the busiest, with 351 flights scheduled in it.
Across the year
Southwest on STL to PHX through the year
June is the worst month at 51.3% on time, 33 points below January, the best at 84.5%. 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. March was the busiest month here, with 163 flights.
Across the week, Tuesday is the strongest day at 77.4% on time and Sunday the weakest at 66.0%. 11 points is a smaller lever than departure hour, but it is free.
Delay causes
Why Southwest runs late on this route
One category carries most of the weight here. Late-arriving aircraft accounts for 59% of the 23,000 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.
- 59%Late-arriving aircraft
- 26%Carrier
- 13%National Airspace System
- 2%Extreme weather
- 0%Security
59% 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 23,000 reported delay minutes here, that single category outweighs weather by 29 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 22,709 reported delay minutes.
The practical consequence: the 5am–8am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 92.9% on time here.
Cancellations are rare at 0.31%, 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
7.3% 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 50 minutes, which a normal layover absorbs.
The 1,262 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 76.7% on time across 1,600 flights, 5 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 5 points of difference.
The sample behind these figures is 1,600 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 Southwest on STL to PHX
Put together: the calendar is the biggest lever here, not the carrier or the hour. January runs 84.5% on time and June 51.3%, a swing of 33 points. If the dates move at all, move them out of June before you think about anything else. 1,593 completed flights over 12 months sit behind that.
Related
Where to go next
- STL to PHX, every carrier
- Southwest on PHX to STL, the return leg
- American Airlines on STL to PHX81.7%
- Southwest Airlines network-wide record
- St. Louis Lambert International (STL) delay statistics
- Phoenix Sky Harbor International (PHX) delay statistics
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.04 million flight records
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.