Carrier route record
WNIAD→PHX
Southwest Airlines · Washington to Phoenix
- Flights
- 275
- Period
- September 2025 to August 2026
- Share of route
- 28%
- Carriers
- 2
Historical statistics for September 2025 to August 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, 6 points worse than the national rate of 77.3%. The late ones land about 45 minutes behind schedule. That rests on 275 flights, with a median arrival 2 minutes late.
The national on-time rate over the same period is 77.3%, so Southwest on IAD to PHX runs 6 points behind the country as a whole. Across a thousand flights that is about 63 extra late arrivals.
Key figures
On time
71.0%
Arrivals under 15 minutes late, of 272 completed flights
Avg delay
45 min
Across delayed arrivals only, not all flights
Cancelled
0.73%
National rate is 1.89%
Whole route
81.2%
Every carrier on IAD to PHX, 979 flights
These figures cover 275 flights between September 2025 and August 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.
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Carrier by carrier
Southwest against every carrier on IAD to PHX
Southwest flew 275 of the 979 flights on IAD to PHX, about 28% of it. Its 71.0% on time is 10 points worse than the route as a whole, which runs 81.2%. Ranked by on-time rate it is last of two carriers on the route, where the range runs from United at 85.2% to Southwest at 71.0%.
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 |
|---|---|---|---|---|---|
| United Airlines | 704 | 85.2% | 66 min | 0.85% | A+ |
| Southwest Airlines (this page)thin sample | 275 | 71.0% | 45 min | 0.73% | C+ |
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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 21 points, against half a point between the best and worst carrier.
- 5am–8am9 flights—
- 8am–11am—
- 11am–2pm1 flights—
- 2pm–5pm156 flights79.2%
- 5pm–8pm109 flights58.3%
- 8pm–5am—
Scale runs 50% to 85%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 58.3% on time, against 79.2% 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 156 flights scheduled in it.
Across the year
Southwest on IAD to PHX through the year
- Jul–Sep 202530 flights—
- Oct–Dec 202591 flights58.9%
- Jan–Mar 202690 flights85.4%
- Apr–Jun 202664 flights73.4%
Scale runs 50% to 90%. Rows with fewer than 30 flights show a dash.
Monthly volumes are too low here to break the year into twelve reliable readings. What the twelve-month total says is 71.0% on time across 275 flights.
Southwest on IAD to PHX did not run the same all year. Its best quarter was Jan–Mar 2026 at 85.4% on time and its weakest Oct–Dec 2025 at 58.9%, a swing of 27 points on roughly 92 flights a quarter. The twelve-month rate averages over that, so if you are flying in a weak quarter the quarter's own figure is the better guide.
Across the week, Saturday is the strongest day at 87.2% on time and Thursday the weakest at 60.5%, a spread of 27 points.
Arrival by arrival
How late Southwest on IAD to PHX runs when it is late
The 79 late arrivals split 36 under half an hour, 28 between 30 and 60 minutes, and 15 an hour or more.
- 15+ min early60 flights22.1%
- Within 15 min133 flights48.9%
- 15–29 min late36 flights13.2%
- 30–59 min late28 flights10.3%
- 1–2 hours late10 flights3.7%
- 2+ hours late5 flights1.8%
Scale runs 0% to 100%.
Share of 272 completed flights by arrival against schedule.
A late pushback is often recovered here: of 113 departures that left 15 minutes late or more, 43 still arrived on time. 9 flights left on time and still arrived late.
The worst days
Worst days for Southwest on IAD to PHX
The latest arrival of the period was on 13 March 2026, 3 hours 25 minutes behind schedule; most of its delay minutes were filed as a late-arriving aircraft. The same cause led on three of the five worst days.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 13 March 2026 | 3 hours 25 minutes | Late-arriving aircraft |
| 27 March 2026 | 3 hours 7 minutes | Late-arriving aircraft |
| 19 February 2026 | 2 hours 24 minutes | Carrier |
| 12 October 2025 | 2 hours 1 minute | Late-arriving aircraft |
| 5 November 2025 | 2 hours 1 minute | National Airspace System |
Delay causes
Why Southwest runs late on this route
Late-arriving aircraft accounts for 56% of the 3,551 delay minutes carriers reported here, and the remaining four split what is left.
- 56%Late-arriving aircraft
- 22%Carrier
- 22%National Airspace System
56% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 3,551 reported delay minutes here, that single category outweighs weather by 56 to one. The split is drawn from 3,551 reported delay minutes.
Cancellations are rare at 0.73%, 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.
Connections and stage length
What a delay here costs
5.5% of arrivals land an hour or more late, close to the national 8.3%, so a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route last about 45 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 74.3% on time across 275 flights, 3 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 3 points of difference.
One caution: this is a thin sample. 275 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. 275 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 71.0% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 272 completed flights over 12 months sit behind that.
Related
Where to go next
- IAD to PHX, every carrier
- Southwest on PHX to IAD, the return leg
- United Airlines on IAD to PHX85.2%
- Southwest Airlines network-wide record
- Washington Dulles International (IAD) 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 7.05 million flight records
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.