Carrier route record

WNPHX→IAD

Southwest Airlines · Phoenix to Washington

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 PHX to IAD sits in the middle of the pack with a C+. Close to three flights in four arrive on time by the DOT's definition, 4 points worse than the national rate of 77.6%. The late ones land about 40 minutes behind schedule. That rests on 337 flights, with a median arrival right on schedule.

The national on-time rate over the same period is 77.6%, so Southwest on PHX to IAD runs 4 points behind the country as a whole. Across a thousand flights that is about 41 extra late arrivals.

On time

73.5%

Arrivals under 15 minutes late, of 332 completed flights

Avg delay

40 min

Across delayed arrivals only, not all flights

Cancelled

0.30%

National rate is 1.81%

Whole route

84.7%

Every carrier on PHX to IAD, 1,098 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 PHX to IAD

Southwest flew 337 of the 1,098 flights on PHX to IAD, about 31% of it. Its 73.5% on time is 11 points worse than the route as a whole, which runs 84.7%. Ranked by on-time rate it is last of two carriers on the route, where the range runs from United at 89.7% to Southwest at 73.5%.

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 IAD
Airline	Flights	On time	Avg delay	Cancelled	Grade
United Airlines	761	89.7%	73 min	0.79%	A+
Southwest Airlines (this page)thin sample	337	73.5%	40 min	0.30%	C+

Departure window

When Southwest runs best on this route

Departure time is the single lever a traveller controls, and it moves the odds more than most people expect. Each bar below is the on-time rate for flights scheduled to leave inside that window, across 337 flights.

5am–8am8 flights—
8am–11am213 flights72.0%
11am–2pm115 flights75.9%
2pm–5pm1 flights—
5pm–8pm—
8pm–5am—

Scale runs 65% to 80%. Rows with fewer than 30 flights show a dash.

The 11am–2pm window is the strongest at 75.9% on time. The full set of windows spans 4 points.

Across the year

Southwest on PHX to IAD through the year

Jul–Sep 202592 flights71.1%
Oct–Dec 202591 flights73.6%
Jan–Mar 202690 flights81.6%
Apr–Jun 202664 flights65.6%

Scale runs 55% to 85%. 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 73.5% on time across 337 flights.

Southwest on PHX to IAD did not run the same all year. Its best quarter was Jan–Mar 2026 at 81.6% on time and its weakest Apr–Jun 2026 at 65.6%, a swing of 16 points on roughly 84 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 81.2% on time and Sunday the weakest at 68.1%. 13 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. Carrier accounts for 47% of the 3,536 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.

Carrier
47%
National Airspace System
26%
Late-arriving aircraft
19%
Security
8%

The largest share of delay minutes, 47%, 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 1,646 of the 3,536 delay minutes reported here. The split is drawn from 3,536 reported delay minutes.

Cancellations are rare at 0.30%, 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

Badly late arrivals are rare here: only 3.3% land an hour or more behind schedule, against 8.1% 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.

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 68.7% on time across 337 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.

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 PHX to IAD

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 73.5% 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