Carrier route record

WNPHX→SEA

Southwest Airlines · Phoenix to Seattle

Flights: 1,037
Period: July 2025 to June 2026
Share of route: 14%
Carriers: 7

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

Southwest on PHX to SEA draws a D+. About one flight in three arrives at least 15 minutes late, and the typical late arrival is roughly 45 minutes behind schedule. Build slack into anything you connect to. That rests on 1,037 flights. The strongest carrier on the route with a full sample, Delta Air Lines, flew 1,764 at 87.8% on time.

Delta Air Lines is the most reliable of the four carriers covered here at 87.8% on time across 1,764 flights.

On time

64.8%

Arrivals under 15 minutes late, of 1,030 completed flights

Avg delay

43 min

Across delayed arrivals only, not all flights

Cancelled

0.58%

National rate is 1.81%

Whole route

82.7%

Every carrier on PHX to SEA, 7,269 flights

These figures cover 1,037 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 SEA

Southwest flew 1,037 of the 7,269 flights on PHX to SEA, about 14% of it. Its 64.8% on time is 18 points worse than the route as a whole, which runs 82.7%. Ranked by on-time rate it is last of seven carriers on the route, where the range runs from Delta at 87.8% to Southwest at 64.8%. Two of those carriers flew fewer than 365 flights here, so treat their positions as rough.

The four carriers here are closely matched: 5 points separate the best from the worst. At that spread, schedule and price are better tie-breakers than reliability. Sample sizes are shown so you can see which rows are worth weighing.

On-time performance by carrier on PHX to SEA
Airline	Flights	On time	Avg delay	Cancelled	Grade
Delta Air Lines	1,764	87.8%	73 min	0.85%	A+
Envoy Air	692	87.1%	45 min	0.00%	A+
Frontier Airlinesthin sample	165	86.1%	80 min	0.00%	A+
Alaska Airlines	2,903	84.9%	56 min	0.76%	B+
SkyWest Airlines	506	82.6%	61 min	0.59%	B+
American Airlinesthin sample	202	81.6%	53 min	0.50%	B+
Southwest Airlines (this page)	1,037	64.8%	43 min	0.58%	D+

No carrier stands out. Delta tops the table at 87.8%, 5 points clear of the bottom, which is inside the range this kind of sample moves year to year.

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 31 points, against 5 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am35 flights82.9%
8am–11am304 flights74.3%
11am–2pm100 flights63.9%
2pm–5pm105 flights64.8%
5pm–8pm193 flights51.6%
8pm–5am300 flights61.7%

Scale runs 45% to 90%. Rows with fewer than 30 flights show a dash.

The 5pm–8pm window is where this operation falls apart: 51.6% on time, against 82.9% 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 8am–11am window is the busiest, with 304 flights scheduled in it.

Across the year

Southwest on PHX to SEA through the year

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

Delays peak in March, when the on-time rate falls to 46.6%. February is the strongest month at 86.6%. Moving a flexible trip across that boundary buys 40 points. July was the busiest month here, with 104 flights.

Across the week, Tuesday is the strongest day at 72.2% on time and Monday the weakest at 56.2%. 16 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 48% of the 16,000 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
48%
Carrier
38%
National Airspace System
13%
Extreme weather
1%
Security
0%

48% 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 16,000 reported delay minutes here, that single category outweighs weather by 48 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 15,748 reported delay minutes.

The largest share of delay minutes, 38%, 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 6,013 of the 16,000 delay minutes reported here.

Cancellations are rare at 0.58%, 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

6.8% 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 1,107 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 69.0% on time across 1,036 flights, 4 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 4 points of difference.

One caution: this is a thin sample. 1,037 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 SEA

Put together: treat all of this as provisional. 1,037 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 64.8% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 1,030 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