Carrier route record

WNPHX→SEA

Southwest Airlines · Phoenix to Seattle

Flights: 1,039
Period: September 2025 to August 2026
Share of route: 14%
Carriers: 7

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

Southwest on PHX to SEA draws a D+. Roughly one flight in three arrives at least 15 minutes late, and the typical late arrival is about 45 minutes behind schedule. Build slack into anything you connect to. That rests on 1,039 flights. The strongest carrier on the route with a full sample, Envoy Air, flew 761 at 87.6% on time.

Envoy Air is the most reliable of the four carriers covered here at 87.6% on time across 761 flights.

On time

62.2%

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

Avg delay

45 min

Across delayed arrivals only, not all flights

Cancelled

0.77%

National rate is 1.89%

Whole route

82.2%

Every carrier on PHX to SEA, 7,202 flights

These figures cover 1,039 flights between September 2025 and August 2026. Beyond the headline rate, 8.2% of arrivals land a full hour or more behind schedule, against 8.3% nationally.

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Carrier by carrier

Southwest against every carrier on PHX to SEA

Southwest flew 1,039 of the 7,202 flights on PHX to SEA, about 14% of it. Its 62.2% on time is 20 points worse than the route as a whole, which runs 82.2%. Ranked by on-time rate it is last of seven carriers on the route, where the range runs from Envoy at 87.6% to Southwest at 62.2%. 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
Envoy Air	761	87.6%	50 min	0.00%	A+
Delta Air Lines	1,767	87.5%	75 min	0.96%	A+
Alaska Airlines	2,886	84.4%	56 min	0.76%	B+
Frontier Airlinesthin sample	116	83.6%	83 min	0.00%	B+
SkyWest Airlines	409	83.0%	63 min	0.49%	B+
American Airlinesthin sample	224	82.5%	63 min	0.45%	B+
Southwest Airlines (this page)	1,039	62.2%	45 min	0.77%	D+

No carrier stands out. Envoy tops the table at 87.6%, 5 points clear of the bottom, which is inside the range this kind of sample moves year to year.

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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 28 points, against 5 points between the best and worst carrier.

5am–8am12 flights—
8am–11am337 flights74.1%
11am–2pm65 flights58.1%
2pm–5pm140 flights62.9%
5pm–8pm178 flights46.3%
8pm–5am307 flights58.1%

Scale runs 40% to 80%. Rows with fewer than 30 flights show a dash.

The 5pm–8pm window is where this operation falls apart: 46.3% on time, against 74.1% for the 8am–11am 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 337 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 107 flights.

Across the week, Tuesday is the strongest day at 68.1% on time and Monday the weakest at 56.4%, a spread of 12 points.

Arrival by arrival

How late Southwest on PHX to SEA runs when it is late

The 389 late arrivals split 170 under half an hour, 135 between 30 and 60 minutes, and 84 an hour or more.

15+ min early131 flights12.7%
Within 15 min510 flights49.5%
15–29 min late170 flights16.5%
30–59 min late135 flights13.1%
1–2 hours late69 flights6.7%
2+ hours late15 flights1.5%

Scale runs 0% to 100%.

Share of 1,030 completed flights by arrival against schedule.

95 of 425 late departures made up the time and arrived on time, 22% of them. In the other direction, 59 flights left on time yet arrived 15 minutes late or more, so that delay built up after pushback: in the air, in a holding pattern or on the ground at SEA.

The worst days

Worst days for Southwest on PHX to SEA

The latest arrival of the period was on 18 May 2026, 8 hours 37 minutes behind schedule; most of its delay minutes were filed as carrier-caused (crew, maintenance, fuelling, baggage). On three of the five worst days the largest share was filed as a late-arriving aircraft.

The latest arrivals of Southwest on PHX to SEA in the period
Date	Arrived late by	Largest filed cause
18 May 2026	8 hours 37 minutes	Carrier
12 August 2026	4 hours 11 minutes	Late-arriving aircraft
18 September 2025	3 hours 51 minutes	Late-arriving aircraft
6 March 2026	2 hours 43 minutes	Late-arriving aircraft
17 February 2026	2 hours 42 minutes	Carrier

Delay causes

Why Southwest runs late on this route

Late-arriving aircraft accounts for 50% of the 17,000 delay minutes carriers reported here, and the remaining four split what is left.

Late-arriving aircraft
50%
Carrier
36%
National Airspace System
13%
Extreme weather
1%
Security
1%

50% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 17,000 reported delay minutes here, that single category outweighs weather by 50 to one. The split is drawn from 17,405 reported delay minutes.

The largest share of delay minutes, 36%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 6,212 of the 17,000 delay minutes reported here.

Cancellations are rare at 0.77%, 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

8.2% 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.

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.

The return leg runs 65.1% on time across 1,042 flights, within 3 points of this direction. The two legs are scored separately because they usually differ; on this city pair they happen not to.

One caution: this is a thin sample. 1,039 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. 1,039 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 62.2% 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, September 2025 to August 2026. Last updated 22 October 2026; recomputed monthly. How this data is collected.

Key figures