Carrier route record
DLPHL→SEA
Delta Air Lines · Philadelphia to Seattle
- Flights
- 113
- Period
- September 2025 to August 2026
- Share of route
- 8%
- Carriers
- 3
Historical statistics for September 2025 to August 2026, not live status. For today’s flights, check with Delta Air Lines.
Delta 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, 8 points worse than the national rate of 77.3%. The late ones land a little over an hour behind schedule. That rests on 113 flights. The strongest carrier on the route with a full sample, American Airlines, flew 661 at 70.8% on time.
The national on-time rate over the same period is 77.3%, so Delta on PHL to SEA runs 8 points behind the country as a whole. Across a thousand flights that is about 79 extra late arrivals.
Key figures
On time
69.4%
Arrivals under 15 minutes late, of 111 completed flights
Avg delay
76 min
Across delayed arrivals only, not all flights
Cancelled
0.88%
National rate is 1.89%
Whole route
69.4%
Every carrier on PHL to SEA, 1,431 flights
These figures cover 113 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
Delta against every carrier on PHL to SEA
Delta flew 113 of the 1,431 flights on PHL to SEA, about 8% of it. Its 69.4% on time is about level with the route as a whole at 69.4%. Ranked by on-time rate it is number two of three carriers on the route, where the range runs from American at 70.8% to Alaska at 68.0%.
The two carriers here are closely matched: 3 points separate the best from the worst. At that spread, schedule and price are better tie-breakers than reliability. Sample sizes are shown so you can see which rows are worth weighing.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| American Airlines | 661 | 70.8% | 53 min | 2.12% | C |
| Delta Air Lines (this page)thin sample | 113 | 69.4% | 76 min | 0.88% | C+ |
| Alaska Airlines | 657 | 68.0% | 51 min | 1.67% | C |
No carrier stands out. American tops the table at 70.8%, 3 points clear of the bottom, which is inside the range this kind of sample moves year to year.
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Departure window
When Delta 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 113 flights.
- 5am–8am82 flights71.6%
- 8am–11am—
- 11am–2pm—
- 2pm–5pm—
- 5pm–8pm31 flights63.3%
- 8pm–5am—
Scale runs 55% to 75%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 63.3% on time, against 71.6% 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 5am–8am window is the busiest, with 82 flights scheduled in it.
Across the year
Delta on PHL to SEA through the year
- Apr–Jun 202651 flights72.5%
- Jul–Sep 202662 flights66.7%
Scale runs 60% to 80%.
Monthly volumes are too low here to break the year into twelve reliable readings. What the twelve-month total says is 69.4% on time across 113 flights.
Split by quarter, Delta on PHL to SEA logged 51 flights in Apr–Jun 2026 and 62 flights in Jul–Sep 2026. Fewer than three of those quarters carried the 30 completed flights this site needs before printing a rate, so the 69.4% annual figure is the one to use.
Arrival by arrival
How late Delta on PHL to SEA runs when it is late
The 34 late arrivals split 11 under half an hour, 15 between 30 and 60 minutes, and 8 an hour or more.
- 15+ min early17 flights15.3%
- Within 15 min60 flights54.1%
- 15–29 min late11 flights9.9%
- 30–59 min late15 flights13.5%
- 1–2 hours late5 flights4.5%
- 2+ hours late3 flights2.7%
Scale runs 0% to 100%.
Share of 111 completed flights by arrival against schedule.
7 of 25 late departures made up the time and arrived on time, 28% of them. In the other direction, 16 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 Delta on PHL to SEA
The latest arrival of the period was on 5 July 2026, 14 hours 21 minutes behind schedule; most of its delay minutes were filed as extreme weather. The five worst days are spread across July, August and June, with no single month standing out.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 5 July 2026 | 14 hours 21 minutes | Extreme weather |
| 21 August 2026 | 4 hours 2 minutes | Late-arriving aircraft |
| 28 August 2026 | 2 hours 38 minutes | Carrier |
| 6 June 2026 | 1 hour 57 minutes | National Airspace System |
| 14 June 2026 | 1 hour 35 minutes | National Airspace System |
Delay causes
Why Delta 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 2,591 reported delay minutes.
- 33%Extreme weather
- 30%National Airspace System
- 19%Carrier
- 17%Late-arriving aircraft
Extreme weather accounts for 33% of delay minutes, well above the single-digit share typical across the system. Weather delays are lumpy: they arrive as whole bad days rather than as a steady drag, so the monthly strip above is the more useful view of the risk. The national share is 6%, so this operation carries roughly 5.5 times the usual weather exposure. The split is drawn from 2,591 reported delay minutes.
Cancellations are rare at 0.88%, below the national 1.89% and low enough to earn the plus on the grade. Roughly one flight in 100 is called off; the risk here is arriving late, not not arriving.
Connections and stage length
What a delay here costs
7.2% 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 a little over an hour, 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 83.2% on time across 114 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. 113 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 Delta on PHL to SEA
Put together: treat all of this as provisional. 113 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 69.4% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 111 completed flights over 12 months sit behind that.
Related
Where to go next
- PHL to SEA, every carrier
- Delta on SEA to PHL, the return leg
- American Airlines on PHL to SEA70.8%
- Alaska Airlines on PHL to SEA68.0%
- Delta Air Lines network-wide record
- Philadelphia International (PHL) delay statistics
- Seattle-Tacoma International (SEA) delay statistics
- The best time of day to fly, according to 7.05 million flight records
- Late aircraft, weather, or the airline: what actually causes US flight delays
Source: US DOT Bureau of Transportation Statistics, on-time performance data, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.