Carrier route record
ASSEA→PHL
Alaska Airlines · Seattle to Philadelphia
- 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 SEA to PHL lands a B, 2 points better than the national rate of 77.6%. About one flight in five arrives 15 minutes late or worse, and those flights are late by roughly 45 minutes on average. That is a workable record, not a spotless one. That rests on 656 flights, with a median arrival 5 minutes early.
The US average over the same twelve months is 77.6%, so there is little to separate Alaska on SEA to PHL from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
79.5%
Arrivals under 15 minutes late, of 644 completed flights
Avg delay
46 min
Across delayed arrivals only, not all flights
Cancelled
1.37%
National rate is 1.81%
Whole route
81.7%
Every carrier on SEA to PHL, 1,326 flights
These figures cover 656 flights between July 2025 and June 2026. The median arrival is 5 minutes early, which is the part an average hides: most flights here are fine, and the on-time rate is decided by a tail of badly late ones. On-time means under 15 minutes late, the DOT's own threshold.
Carrier by carrier
Alaska against every carrier on SEA to PHL
Alaska flew 656 of the 1,326 flights on SEA to PHL, about 49% of it. Its 79.5% on time is 2 points worse than the route as a whole, which runs 81.7%. Ranked by on-time rate it is last of three carriers on the route, where the range runs from Delta at 84.3% to Alaska at 79.5%. 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 |
|---|---|---|---|---|---|
| Delta Air Linesthin sample | 51 | 84.3% | 41 min | 0.00% | B+ |
| American Airlines | 619 | 83.9% | 83 min | 2.10% | B |
| Alaska Airlines (this page) | 656 | 79.5% | 46 min | 1.37% | B |
Flight by flight
Alaska flight numbers on SEA to PHL
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 12 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–8am—
- 8am–11am364 flights74.1%
- 11am–2pm—
- 2pm–5pm—
- 5pm–8pm—
- 8pm–5am292 flights86.2%
Scale runs 65% to 90%. Rows with fewer than 30 flights show a dash.
The overnight block holds up unusually well at 86.2% on time across 292 flights. Red-eyes fly into empty airspace and empty gates, and they are the first rotation of the aircraft's day rather than the last. The 8am–11am window is the busiest, with 364 flights scheduled in it.
Across the year
Alaska on SEA to PHL through the year
July is the worst month at 61.4% on time, 35 points below April, the best at 96.7%. Summer afternoon convection and peak-season schedules land on the same weeks every year, so this is a pattern you can book around rather than a run of bad luck. May was the busiest month here, with 62 flights.
Across the week, Tuesday is the strongest day at 86.2% on time and Thursday the weakest at 75.0%. 11 points is a smaller lever than departure hour, but it is free.
Delay causes
Why Alaska runs late on this route
Carriers report a reason for every delay minute they cause, in five DOT categories. The split below is by minutes, not by number of flights, so a handful of very long weather delays weighs as much as many short ones. It covers 6,122 reported delay minutes.
- 37%Carrier
- 32%Late-arriving aircraft
- 21%National Airspace System
- 11%Extreme weather
The largest share of delay minutes, 37%, 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 2,240 of the 6,122 delay minutes reported here. The split is drawn from 6,122 reported delay minutes.
Cancellations sit at 1.37% against a national 1.81%, which is ordinary. Diversions add another 0.46%.
Connections and stage length
What a delay here costs
Badly late arrivals are rare here: only 4.0% 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 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 65.6% on time across 656 flights, 14 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 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 SEA to PHL
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 79.5% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 644 completed flights over 12 months sit behind that.
Related
Where to go next
- SEA to PHL, every carrier
- Alaska on PHL to SEA, the return leg
- American Airlines on SEA to PHL83.9%
- Alaska Airlines network-wide record
- Seattle-Tacoma International (SEA) delay statistics
- Philadelphia International (PHL) delay statistics
- The best time of day to fly, according to 7.04 million flight records
- Worst months to fly in the US, ranked by the data
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.