Carrier route record

ASIAD→SEA

Alaska Airlines · Washington to Seattle

Flights: 835
Period: July 2025 to June 2026
Share of route: 44%
Carriers: 3

Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Alaska Airlines.

Alaska on IAD to SEA sits in the middle of the pack with a C. Close to three flights in four arrive on time by the DOT's definition, 4 points worse than the national rate of 77.6%. The late ones land roughly 55 minutes behind schedule. That rests on 835 flights, with a median arrival 3 minutes early.

The US average over the same twelve months is 77.6%, so there is little to separate Alaska on IAD to SEA from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.

On time

73.7%

Arrivals under 15 minutes late, of 825 completed flights

Avg delay

53 min

Across delayed arrivals only, not all flights

Cancelled

1.20%

National rate is 1.81%

Whole route

76.6%

Every carrier on IAD to SEA, 1,884 flights

These figures cover 835 flights between July 2025 and June 2026. The median arrival is 3 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 IAD to SEA

Alaska flew 835 of the 1,884 flights on IAD to SEA, about 44% of it. Its 73.7% on time is 3 points worse than the route as a whole, which runs 76.6%. Ranked by on-time rate it is last of three carriers on the route, where the range runs from United at 79.7% to Alaska at 73.7%. 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.

On-time performance by carrier on IAD to SEA
Airline	Flights	On time	Avg delay	Cancelled	Grade
United Airlines	688	79.7%	62 min	0.58%	B+
Delta Air Linesthin sample	361	77.2%	93 min	1.39%	B
Alaska Airlines (this page)	835	73.7%	53 min	1.20%	C

Flight by flight

Alaska flight numbers on IAD to SEA

AS 35107:0079.9% · 306 flights

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 26 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–8am327 flights79.7%
8am–11am186 flights85.9%
11am–2pm—
2pm–5pm—
5pm–8pm322 flights60.3%
8pm–5am—

Scale runs 50% to 90%. Rows with fewer than 30 flights show a dash.

The 5pm–8pm window is where this operation falls apart: 60.3% on time, against 85.9% 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 5am–8am window is the busiest, with 327 flights scheduled in it.

Across the year

Alaska on IAD to SEA through the year

Darker means more delays. Figures are on-time percentages.September best, December worst

December is the weak month at 21.6% on time, against 92.2% in September. 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. August was the busiest month here, with 93 flights.

Across the week, Thursday is the strongest day at 79.3% on time and Monday the weakest at 70.4%. 9 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 11,000 reported delay minutes.

National Airspace System
35%
Late-arriving aircraft
29%
Carrier
23%
Extreme weather
11%
Security
2%

35% 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 4,009 minutes out of 11,000, against a national NAS share of 21%. The split is drawn from 11,453 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 85.9% on time here.

Cancellations sit at 1.20% against a national 1.81%, which is ordinary. Diversions add another 0.00%.

Connections and stage length

What a delay here costs

7.4% 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 55 minutes, which a normal layover absorbs.

At 2,305 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 80.4% on time across 835 flights, 7 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 7 points of difference.

One caution: this is a thin sample. 835 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 IAD to SEA

Put together: treat all of this as provisional. 835 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 73.7% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 825 completed flights over 12 months sit behind that.

Where to go next

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.

Key figures