Carrier route record
ASPHL→SEA
Alaska Airlines · Philadelphia to Seattle
- Flights
- 656
- Period
- July 2025 to June 2026
- Share of route
- 49%
- Carriers
- 3
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Alaska Airlines.
Alaska on PHL to SEA draws a C. About one flight in three arrives at least 15 minutes late, and the typical late arrival is about 55 minutes behind schedule. Build slack into anything you connect to. That rests on 656 flights, with a median arrival 1 minute late.
The national on-time rate over the same period is 77.6%, so Alaska on PHL to SEA runs 12 points behind the country as a whole. Across a thousand flights that is about 120 extra late arrivals.
Key figures
On time
65.6%
Arrivals under 15 minutes late, of 645 completed flights
Avg delay
54 min
Across delayed arrivals only, not all flights
Cancelled
1.52%
National rate is 1.81%
Whole route
69.5%
Every carrier on PHL to SEA, 1,327 flights
These figures cover 656 flights between July 2025 and June 2026. Beyond the headline rate, 9.8% of arrivals land a full hour or more behind schedule. That is the number that wrecks a connection, and it is not visible in an on-time percentage alone.
Carrier by carrier
Alaska against every carrier on PHL to SEA
Alaska flew 656 of the 1,327 flights on PHL to SEA, about 49% of it. Its 65.6% on time is 4 points worse than the route as a whole, which runs 69.5%. Ranked by on-time rate it is last of three carriers on the route, where the range runs from American at 73.4% to Alaska at 65.6%. 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.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| American Airlines | 620 | 73.4% | 49 min | 2.26% | C |
| Delta Air Linesthin sample | 51 | 72.5% | 52 min | 0.00% | C+ |
| Alaska Airlines (this page) | 656 | 65.6% | 54 min | 1.52% | C |
Flight by flight
Alaska flight numbers on PHL to SEA
Departure window
When Alaska runs best on this route
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 11 points, against half a point between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am293 flights70.8%
- 8am–11am—
- 11am–2pm—
- 2pm–5pm21 flights—
- 5pm–8pm342 flights60.3%
- 8pm–5am—
Scale runs 50% to 75%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 60.3% on time, against 70.8% 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 342 flights scheduled in it.
Across the year
Alaska on PHL to SEA through the year
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, Tuesday is the strongest day at 77.1% on time and Monday the weakest at 56.4%. 21 points is a smaller lever than departure hour, but it is free.
Delay causes
Why Alaska runs late on this route
One category carries most of the weight here. National Airspace System accounts for 43% of the 12,000 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.
- 43%National Airspace System
- 34%Late-arriving aircraft
- 20%Carrier
- 3%Extreme weather
- 0%Security
34% 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 12,000 reported delay minutes here, that single category outweighs weather by 11 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 11,994 reported delay minutes.
43% 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 5,120 minutes out of 12,000, against a national NAS share of 21%.
Cancellations sit at 1.52% against a national 1.81%, which is ordinary. Diversions add another 0.15%.
Connections and stage length
What a delay here costs
For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 9.8% of arrivals land a full hour or more behind schedule, against 8.1% nationally. A 45-minute layover does not survive that, and no amount of walking quickly changes it. Ninety minutes is the honest minimum here, and two hours if the onward flight is on a separate ticket.
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 79.5% on time across 656 flights, 14 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 14 points of difference.
One caution: this is a thin sample. 656 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. 656 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 65.6% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 645 completed flights over 12 months sit behind that.
Related
Where to go next
- PHL to SEA, every carrier
- Alaska on SEA to PHL, the return leg
- American Airlines on PHL to SEA73.4%
- Alaska Airlines network-wide record
- Philadelphia International (PHL) delay statistics
- Seattle-Tacoma International (SEA) delay statistics
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.04 million flight records
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.