Carrier route record

ASPHL→SEA

Alaska Airlines · Philadelphia to Seattle

Flights: 657
Period: September 2025 to August 2026
Share of route: 46%
Carriers: 3

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

Alaska on PHL to SEA 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 77.3%. The late ones land roughly 50 minutes behind schedule. That rests on 657 flights, with a median arrival 1 minute late.

The national on-time rate over the same period is 77.3%, so Alaska on PHL to SEA runs 9 points behind the country as a whole. Across a thousand flights that is about 93 extra late arrivals.

On time

68.0%

Arrivals under 15 minutes late, of 646 completed flights

Avg delay

51 min

Across delayed arrivals only, not all flights

Cancelled

1.67%

National rate is 1.89%

Whole route

69.4%

Every carrier on PHL to SEA, 1,431 flights

These figures cover 657 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

Alaska against every carrier on PHL to SEA

Alaska flew 657 of the 1,431 flights on PHL to SEA, about 46% of it. Its 68.0% on time is about level with the route as a whole at 69.4%. Ranked by on-time rate it is last of three carriers on the route, where the range runs from American at 70.8% to Alaska at 68.0%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.

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 PHL to SEA
Airline	Flights	On time	Avg delay	Cancelled	Grade
American Airlines	661	70.8%	53 min	2.12%	C
Delta Air Linesthin sample	113	69.4%	76 min	0.88%	C+
Alaska Airlines (this page)	657	68.0%	51 min	1.67%	C

Flight by flight

Alaska flight numbers on PHL to SEA

AS 44316:2663.9% · 333 flights

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Departure window

When Alaska 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 657 flights.

5am–8am293 flights72.6%
8am–11am—
11am–2pm—
2pm–5pm70 flights66.2%
5pm–8pm294 flights63.7%
8pm–5am—

Scale runs 55% to 80%. Rows with fewer than 30 flights show a dash.

The 5pm–8pm window is where this operation falls apart: 63.7% on time, against 72.6% 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 5pm–8pm window is the busiest, with 294 flights scheduled in it.

Across the year

Alaska on PHL to SEA through the year

Darker means more delays. Figures are on-time percentages.May best, December worst

December is the weak month at 37.1% on time, against 82.0% in May. Winter delays cluster: a single storm system can account for most of a month's shortfall, so an average December hides both very good weeks and genuinely unflyable days. May was the busiest month here, with 62 flights.

Across the week, Saturday is the strongest day at 71.0% on time and Monday the weakest at 63.5%, a spread of 8 points.

Arrival by arrival

How late Alaska on PHL to SEA runs when it is late

Alaska on PHL to SEA often beats the schedule: 171 of 646 completed flights, 26%, arrived 15 minutes or more early. The 207 late arrivals split 74 under half an hour, 82 between 30 and 60 minutes, and 51 an hour or more.

15+ min early171 flights26.5%
Within 15 min268 flights41.5%
15–29 min late74 flights11.5%
30–59 min late82 flights12.7%
1–2 hours late38 flights5.9%
2+ hours late13 flights2.0%

Scale runs 0% to 100%.

Share of 646 completed flights by arrival against schedule.

37 of 138 late departures made up the time and arrived on time, 27% of them. In the other direction, 106 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 Alaska on PHL to SEA

The latest arrival of the period was on 21 May 2026, 6 hours 2 minutes behind schedule; most of its delay minutes were filed as extreme weather. The five worst days are spread across May, July, June and August, with no single month standing out.

The latest arrivals of Alaska on PHL to SEA in the period
Date	Arrived late by	Largest filed cause
21 May 2026	6 hours 2 minutes	Extreme weather
28 July 2026	4 hours 36 minutes	National Airspace System
10 June 2026	3 hours 55 minutes	National Airspace System
20 August 2026	3 hours 23 minutes	Carrier
27 August 2026	2 hours 38 minutes	Late-arriving aircraft

Delay causes

Why Alaska runs late on this route

National Airspace System accounts for 50% of the 11,000 delay minutes carriers reported here, and the remaining four split what is left.

National Airspace System
50%
Late-arriving aircraft
27%
Carrier
20%
Extreme weather
3%
Security
0%

50% of delay minutes are charged to the National Airspace System: air traffic volume, runway configuration, ground stops. No carrier can price its way out of that, which is why airport choice moves the number here more than carrier choice does. That is 5,341 minutes out of 11,000, against a national NAS share of 21%. The split is drawn from 10,585 reported delay minutes.

Cancellations sit at 1.67% against a national 1.89%, which is ordinary. Diversions add another 0.00%.

Connections and stage length

What a delay here costs

7.9% 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 roughly 50 minutes, which a normal layover absorbs.

At 2,379 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 80.7% on time across 657 flights, 13 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 13 points of difference.

One caution: this is a thin sample. 657 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 Alaska on PHL to SEA

Put together: treat all of this as provisional. 657 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 68.0% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 646 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