Carrier route record

WNPHX→STL

Southwest Airlines · Phoenix to St. Louis

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 PHX to STL lands a B+, about a point worse than the national rate of 77.6%. About one flight in four arrives 15 minutes late or worse, and those flights are late by roughly 45 minutes on average. That is a workable record, not a spotless one. That rests on 1,600 flights, with a median arrival 1 minute early.

The US average over the same twelve months is 77.6%, so there is little to separate Southwest on PHX to STL from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.

On time

76.7%

Arrivals under 15 minutes late, of 1,585 completed flights

Avg delay

47 min

Across delayed arrivals only, not all flights

Cancelled

0.19%

National rate is 1.81%

Whole route

77.8%

Every carrier on PHX to STL, 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 PHX to STL

Southwest flew 1,600 of the 2,284 flights on PHX to STL, most of the route. Its 76.7% on time is about level with the route as a whole at 77.8%. Ranked by on-time rate it is last of five carriers on the route, where the range runs from Envoy at 93.3% to Southwest at 76.7%. 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.

On-time performance by carrier on PHX to STL
Airline	Flights	On time	Avg delay	Cancelled	Grade
Envoy Airthin sample	30	93.3%	77 min	0.00%	A+
SkyWest Airlinesthin sample	54	85.2%	35 min	0.00%	A+
Frontier Airlinesthin sample	53	82.7%	170 min	1.89%	B
American Airlines	547	79.1%	69 min	0.73%	B+
Southwest Airlines (this page)	1,600	76.7%	47 min	0.19%	B+

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 48 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–8am348 flights94.8%
8am–11am304 flights86.4%
11am–2pm301 flights79.2%
2pm–5pm277 flights61.7%
5pm–8pm261 flights66.8%
8pm–5am109 flights46.7%

Scale runs 40% to 100%. Rows with fewer than 30 flights show a dash.

The 8pm–5am window is where this operation falls apart: 46.7% on time, against 94.8% 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 348 flights scheduled in it.

Across the year

Southwest on PHX to STL through the year

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

June is the worst month at 66.7% on time, 18 points below February, the best at 84.7%. 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 164 flights.

Across the week, Wednesday is the strongest day at 82.4% on time and Sunday the weakest at 70.0%. 12 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 51% of the 17,000 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.

Late-arriving aircraft
51%
Carrier
39%
National Airspace System
8%
Security
1%
Extreme weather
1%

51% 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 17,000 reported delay minutes here, that single category outweighs weather by 51 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 17,163 reported delay minutes.

The largest share of delay minutes, 39%, 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 6,670 of the 17,000 delay minutes reported here.

Cancellations are rare at 0.19%, 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

5.4% 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 45 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 72.2% on time across 1,600 flights, 5 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 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 PHX to STL

Put together: the calendar is the biggest lever here, not the carrier or the hour. February runs 84.7% on time and June 66.7%, a swing of 18 points. If the dates move at all, move them out of June before you think about anything else. 1,585 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