Carrier route record

WNIAD→PHX

Southwest Airlines · Washington to Phoenix

Flights: 337
Period: July 2025 to June 2026
Share of route: 31%
Carriers: 2

Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Southwest Airlines.

Southwest on IAD 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, 9 points worse than the national rate of 77.6%. The late ones land roughly 50 minutes behind schedule. That rests on 337 flights, with a median arrival 4 minutes late.

The national on-time rate over the same period is 77.6%, so Southwest on IAD to PHX runs 9 points behind the country as a whole. Across a thousand flights that is about 89 extra late arrivals.

On time

68.7%

Arrivals under 15 minutes late, of 332 completed flights

Avg delay

48 min

Across delayed arrivals only, not all flights

Cancelled

0.89%

National rate is 1.81%

Whole route

79.9%

Every carrier on IAD to PHX, 1,097 flights

These figures cover 337 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 IAD to PHX

Southwest flew 337 of the 1,097 flights on IAD to PHX, about 31% of it. Its 68.7% on time is 11 points worse than the route as a whole, which runs 79.9%. Ranked by on-time rate it is last of two carriers on the route, where the range runs from United at 84.9% to Southwest at 68.7%.

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 IAD to PHX
Airline	Flights	On time	Avg delay	Cancelled	Grade
United Airlines	760	84.9%	77 min	0.79%	B+
Southwest Airlines (this page)thin sample	337	68.7%	48 min	0.89%	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 23 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–8am9 flights—
8am–11am—
11am–2pm1 flights—
2pm–5pm180 flights78.5%
5pm–8pm147 flights55.9%
8pm–5am—

Scale runs 45% to 85%. Rows with fewer than 30 flights show a dash.

The 5pm–8pm window is where this operation falls apart: 55.9% on time, against 78.5% for the 2pm–5pm 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 2pm–5pm window is the busiest, with 180 flights scheduled in it.

Across the year

Southwest on IAD to PHX through the year

Darker means more delays. Figures are on-time percentages.January best, July worst

July is the worst month at 43.3% on time, 47 points below January, the best at 90.0%. 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. January was the busiest month here, with 31 flights.

Across the week, Saturday is the strongest day at 83.3% on time and Thursday the weakest at 58.7%. 25 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 57% of the 5,030 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
57%
National Airspace System
22%
Carrier
20%
Extreme weather
1%

57% 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 5,030 reported delay minutes here, that single category outweighs weather by 57 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 5,030 reported delay minutes.

Cancellations are rare at 0.89%, 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

7.2% 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.

At 1,956 miles this is transcontinental flying, and long routes get a quiet structural advantage. Scheduled block time on a flight this length carries more padding in absolute minutes, so a twenty-minute late departure often still becomes an on-time arrival. Read the on-time rate here as slightly flattering next to a short-haul route with the same operational quality.

The return leg is a different operation and performs like one: it runs 73.5% on time across 337 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.

One caution: this is a thin sample. 337 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 Southwest on IAD to PHX

Put together: treat all of this as provisional. 337 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 68.7% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 332 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