Route profile
SEA→PHL
Flight reliability, delays and best times to fly from Seattle to Philadelphia, 2,378 miles.
Right now
Aviation weather is not currently a factor.
Aviation weather is not currently a factor.
Route reliability
July 2023 – July 2026
Better than 51% of comparable major US routes (4,598 compared)
Calculated from 3,616 flights. How this is calculated
SEA → PHL arrives on time 75.8% of the time; the return trip, PHL → SEA, arrives on time 69.9% of the time, a 5.9-point gap between the two directions of the same city pair.
SEA → PHL spends 30.4 minutes on the ground on a 2,378-mile trip: 22.1 minutes from pushback to wheels-up at SEA and 8.3 minutes from touchdown to gate at PHL.
Source: US DOT Bureau of Transportation Statistics · Data covering July 2023 – July 2026
What stands out
Unlike most, it barely matters what time you fly this route, a steadier spread than 99% of 4,023 comparable routes.
77.2% on time for 9 PM–5 AM departures, against 73.4% for 12–3 PM, a narrow gap either way.
Source: FlyerIntel analysis of US DOT BTS data · July 2023 – July 2026 · Ranked against every other route with the same kind of figure and at least 4,023 in the comparison.
What sets this route apart
Where SEA to PHL differs most from similar routes by hour, weekday, month and airline, July 2023 – July 2026.
SEA to PHL struggles most at 8 AM: 71.6% of its flights scheduled then arrive on time, 11.9 points behind the 83.5% on routes of similar length at the same hour. Against all other routes the gap is 14.3 points.
Thursday is the day SEA to PHL slips furthest against routes of similar length, 73.3% on time where they average 77.3%, 4 points lower.
In August, SEA to PHL runs 9.2 points below routes of similar length, 67.6% on time to 76.8%. Against all other routes the gap is 8.9 points.
SEA to PHL against comparable routes
July 2023 – July 2026| Measure | This route | Compared with | Them | Gap | Flights behind it |
|---|---|---|---|---|---|
| Hour: 8 AM departures | 71.6% | routes of similar length | 83.5% | −11.9 pts | 222 here, 109,354 there |
| Weekday: Thursday | 73.3% | routes of similar length | 77.3% | −4.0 pts | 517 here, 160,350 there |
| Month: August | 67.6% | routes of similar length | 76.8% | −9.2 pts | 374 here, 94,723 there |
Each comparison pools the flights of other routes, with this route’s own left out. Similar length means within 15% of this route’s 2,378 miles, with at least 5 such routes. A bucket is set against the most comparable group that has enough flights: similar length, then the same origin (at least 3 routes), then all other routes. Hours, weekdays and months appear only where both sides have 120 completed flights, and airlines where both have 600. The gap must be at least 2 points and 2 standard errors, and only the largest gap each way is kept per measure. These are differences in the flights counted, not causes.
Why SEA → PHL flights are cancelled
July 2023 – July 2026
SEA → PHL cancelled 52 of 3,616 scheduled flights — about 1 in every 70. The reason filed most often was extreme weather, 59.6% of the cancellations coded on this route — about 1 in every 117 scheduled flights.
Share of cancellations
Of 52 cancelled departures carrying a reason code.
What each reason means
Conditions the carrier judged severe enough to stop the flight: a blizzard, a hurricane, a line of thunderstorms.
31 cancellations, 59.6% of the total.
Crew, maintenance, aircraft cleaning, baggage or fueling: what BTS counts as within the carrier’s own control.
18 cancellations, 34.6% of the total.
Airport capacity, air traffic control flow programs, heavy traffic and ordinary bad weather. A system decision, not the airline’s.
3 cancellations, 5.8% of the total.
A terminal evacuation, a security breach, screening equipment failure, or screening queues over 29 minutes.
0 cancellations, 0.0% of the total.
Reason codes are the operating airline’s own filing with US DOT, not an independent finding of fault. With only one or two carriers on the route, the split mostly reflects how they file. Ordinary bad weather is filed under air traffic, so weather’s full share is larger than its bar.
52 coded cancellations were recorded on SEA → PHL; the section appears from 50.
When it goes wrong
July 2023 – July 2026
35 min late
against a median of 3 min early
Percentiles over 3,616 operations; cancelled and diverted flights are counted separately.
Will your connection be tight enough?
Layovers at PHL after arriving from SEA.
| Connection time | Chance of missing | Reads as |
|---|---|---|
| 30 min | 43% | Likely to miss |
| 45 min | 23% | High risk |
| 60 min | 12% | Some risk |
| 90 min | 4.9% | Low risk |
| 120 min | 2.8% | Low risk |
This is one leg of a connection. Gate changes and the next flight's own schedule matter too. And a connection can fail before delay is even the question — this route cancels 1.44% of the time and diverts 0.47% of the time, which a late arrival never shows up in.
Chance of missing is the share of 3,547 arrivals on this route that landed later than the connection time less 30 minutes to reach the next gate.
The worst tenth of arrivals on this route land at least 35 minutes late (90th-percentile gate arrival delay), over 3,616 operations.
Any other layover length: connection checker.
Best time to fly
SEA → PHL flights departing 9 PM–5 AM arrived on time 77.2% of the time, against 73.4% for 12–3 PM departures, a gap of 3.8 percentage points.
By departure window
By departure hour
- 12 AM to 7 AM: too few flights to score
- 8 AM: 71.6% on time from 231 flights
- 9 AM: 74.6% on time from 1,031 flights
- 10 AM to 11 AM: too few flights to score
- 12 PM: 73.1% on time from 406 flights
- 1 PM to 8 PM: too few flights to score
- 9 PM: 75.5% on time from 777 flights
- 10 PM: 80.9% on time from 688 flights
- 11 PM: 74.1% on time from 405 flights
Departure windows with fewer than 120 flights are not scored.
Why SEA → PHL runs late
July 2023 – July 2026
crew, maintenance, boarding and fueling, all within the carrier’s control
the inbound aircraft was late, so this flight started late
airspace and airport capacity, including weather-driven flow control
weather severe enough to stop this flight specifically
screening or terminal security incidents
Share of the delay minutes US DOT attributed to each cause for SEA → PHL. Only delays of 15 minutes or more are attributed.
Airlines on this route
Carriers with at least 200 flights, by the airline that operated each one.
| Carrier | Flights | On time | Cancelled | Median delay | Severe |
|---|---|---|---|---|---|
| Alaska Airlines | 1,969 | 74.7% | 0.86% | -1 min | 3.7% |
| American Airlines | 1,564 | 76.7% | 2.17% | -6 min | 6.8% |
Alaska Airlines flew 55.7% of the 3,533 flights listed. American Airlines cancelled 2.17% of its flights here against 0.86% for Alaska Airlines.
American Airlines arrived on time 2.0 percentage points more often than Alaska Airlines on this route.
Flights on this route
Flight numbers with at least 600 operations here and still on the schedule.
| Flight | Scheduled | Operations | On time |
|---|---|---|---|
| AS442 Alaska Airlines | 9:40 AM | 1,111 | 73.1% |
Weekly and seasonal patterns
By day of week
Wednesday is historically the most reliable day and Sunday the least, a gap of 8.0 percentage points.
By month
- Jan: 74.3%
- Feb: 85.3%
- Mar: 84.4%
- Apr: 84.7%
- May: 74.9%
- Jun: 73.9%
- Jul: 68.4%
- Aug: 67.6%
- Sep: 73.1%
- Oct: 78.6%
- Nov: 82.9%
- Dec: 79.5%
August is historically the weakest month and February the strongest, a spread of 17.7 percentage points.
Reliability over time
July 2023 – July 2026
- July 2023: 73.3% from 125 flights
- August 2023: 82.9% from 124 flights
- September 2023: 76.7% from 120 flights
- October 2023: too few flights to score (97)
- November 2023: too few flights to score (85)
- December 2023: too few flights to score (62)
- January 2024: too few flights to score (59)
- February 2024: too few flights to score (54)
- March 2024: too few flights to score (73)
- April 2024: too few flights to score (85)
- May 2024: too few flights to score (93)
- June 2024: too few flights to score (116)
- July 2024: 53.7% from 123 flights
- August 2024: 46.6% from 124 flights
- September 2024: too few flights to score (91)
- October 2024: too few flights to score (77)
- November 2024: too few flights to score (74)
- December 2024: too few flights to score (86)
- January 2025: too few flights to score (38)
- February 2025: too few flights to score (36)
- March 2025: too few flights to score (72)
- April 2025: too few flights to score (82)
- May 2025: too few flights to score (93)
- June 2025: too few flights to score (116)
- July 2025: 67.0% from 123 flights
- August 2025: 71.9% from 136 flights
- September 2025: 80.0% from 121 flights
- October 2025: 86.8% from 123 flights
- November 2025: too few flights to score (87)
- December 2025: too few flights to score (93)
- January 2026: too few flights to score (67)
- February 2026: too few flights to score (55)
- March 2026: too few flights to score (76)
- April 2026: too few flights to score (114)
- May 2026: 82.2% from 158 flights
- June 2026: 86.9% from 173 flights
- July 2026: 76.1% from 185 flights
Over the most recent 12 months (2025-08 to 2026-07), on-time arrivals averaged 82.2% against 70.1% in the 12 months before — improving by 12.1 percentage points.
Data and methodology
Calculated by FlyerIntel from 3,616 SEA → PHL flight records from the US DOT Bureau of Transportation Statistics, covering July 2023 – July 2026. Late means 15 or more minutes past scheduled arrival; cancelled and diverted flights are left out of on-time rates.
Full methodology · Data sources · Report a problem
Related research: How Long a Layover Needs to Be · Two Airlines on One Route · Best Time of Day to Fly From Major US Airports
Analysis last recomputed