Route reliability record
PHL→SEA
Philadelphia to Seattle
- Flights
- 1,327
- Period
- July 2025 to June 2026
- Distance
- 2,379 mi
- Carriers
- 3
This route sits in the middle of the pack with a C. About seven flights in ten arrive on time by the DOT's definition, 8 points worse than the national rate of 77.6%. The late ones land roughly 50 minutes behind schedule. That rests on 1,327 PHL to SEA flights, of which American Airlines flew 620 at 73.4% on time.
Best time to fly PHL to SEA: a 8am–11am departure, ideally on a Tuesday. Flights in that window arrived on time 83.6% of the time and Tuesday flights 78.4%, against 69.5% for the route overall.
The national on-time rate over the same period is 77.6%, so this route runs 8 points behind the country as a whole. Across a thousand flights that is about 81 extra late arrivals.
Key figures
On time
69.5%
Arrivals under 15 minutes late, of 1,301 completed flights
Avg delay
52 min
Across delayed arrivals only, not all flights
Cancelled
1.81%
National rate is 1.81%
Best carrier
American
73.4% on time across 620 flights
These figures cover 1,327 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
Which airline is most reliable on PHL to SEA
The choice of carrier is not cosmetic here. American Airlines arrives on time 73.4% of the time; Alaska Airlines manages 65.6%. Sample sizes sit next to every figure, because a two-point gap across 656 flights means less than a ten-point one.
| 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 | 656 | 65.6% | 54 min | 1.52% | C |
American leads Alaska by 8 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.
Flight by flight
Flights on PHL to SEA
The flight numbers below flew this route at least 250 times in the period, busiest first. Each has its own record, with its schedule and delay causes.
Best ways to make this trip
The most reliable ways to fly Philadelphia to Seattle
Every airline on this route, ranked by how often a scheduled flight actually operated and arrived on time, with its best departure time and most punctual flight number. No nearby airport pair beat these.
| Option | Airline | Success | On time | Cancelled | Best departure | Most punctual flight |
|---|---|---|---|---|---|---|
| 1. PHL → SEAPhiladelphia to Seattle | American Airlines | 71.7% | 73.4% | 2.26% | 8am–11am, Tue | — |
| 2. PHL → SEAPhiladelphia to Seattle | Alaska Airlines | 64.6% | 65.6% | 1.52% | 5am–8am, Tue | AS 443 18:52 |
Success is the share of scheduled flights that operated and arrived less than 15 minutes late, so a cancelled flight counts against it. “(route)” means the best time comes from every carrier on the route rather than this airline alone.
Departure window
The best time of day to leave
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 19 points, against 8 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am319 flights71.6%
- 8am–11am208 flights83.6%
- 11am–2pm—
- 2pm–5pm40 flights76.3%
- 5pm–8pm760 flights64.3%
- 8pm–5am—
Scale runs 55% to 90%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 64.3% on time, against 83.6% 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 5pm–8pm window is the busiest, with 760 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 49 points from best month to worst, which is wide. An annual average tells you very little about the week you are actually flying, so read the strip rather than the headline if your dates are fixed.
December is the weak month at 38.0% on time, against 86.8% in February. 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. June was the busiest month here, with 174 flights.
Across the week, Tuesday is the strongest day at 78.4% on time and Friday the weakest at 64.5%. 14 points is a smaller lever than departure hour, but it is free.
Delay causes
Why this route gets delayed
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 21,000 reported delay minutes.
- 41%National Airspace System
- 28%Late-arriving aircraft
- 26%Carrier
- 4%Extreme weather
- 0%Security
41% 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 8,538 minutes out of 21,000, against a national NAS share of 21%. The split is drawn from 20,603 reported delay minutes.
The practical consequence: the 8am–11am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 83.6% on time here.
Cancellations sit at 1.81% against a national 1.81%, which is ordinary. Diversions add another 0.15%.
Connections and stage length
What a delay here actually costs
7.8% 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 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 81.7% on time across 1,326 flights, 12 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 12 points of difference.
The sample behind these figures is 1,327 flights, enough that the headline rate is stable to within roughly a point. The hour-block and month splits divide that further, so read the thinner bars with more caution than the headline.
Work out the risk of missing a connection in SEA after this flight
What to do with this
Booking this route
Put together: the calendar is the biggest lever here, not the carrier or the hour. February runs 86.8% on time and December 38.0%, a swing of 49 points. If the dates move at all, move them out of December before you think about anything else. 1,301 completed flights over 12 months sit behind that.
Common questions
PHL to SEA questions
How often is PHL to SEA delayed?
Roughly one flight in three arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 30.5% of the 1,327 flights in this analysis, against 22.4% nationally. Delayed flights are late by roughly 50 minutes on average.
Which airline is most reliable on PHL to SEA?
American Airlines leads at 73.4% on time across 620 flights. Alaska Airlines is at the other end on 65.6%, a gap of 8 points. Sample size matters as much as the percentage: a rate built from a few hundred flights moves around far more than one built from ten thousand.
What time of day has the fewest delays on PHL to SEA?
The 8am–11am departure window is the strongest at 83.6% on time. The 5pm–8pm window is the weakest at 64.3%, 19 points behind. Later departures inherit delays from earlier flights the same aircraft has already flown, which is why the curve slopes the way it does.
How bad are December delays on PHL to SEA?
December is the weakest month at 38.0% on time, compared with 86.8% in February. Across the year that is 49 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.
Related
Where to go next
- SEA to PHL — the return legseparate record
- Philadelphia International (PHL) delay statistics
- Seattle-Tacoma International (SEA) delay statistics
- American Airlines on PHL to SEA73.4%
- Alaska Airlines on PHL to SEA65.6%
- PHL to ATL, a related route79.2%
- LAX to SEA, a related route85.4%
- PHL to MCO, a related route72.4%
- American Airlines on-time record73.4%
- Delta Air Lines on-time record72.5%
- Alaska Airlines on-time record65.6%
- 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
Direction matters. PHL to SEA and SEA to PHL are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.
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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.