Carrier route record

ASSLC→SEA

Alaska Airlines · Salt Lake City to Seattle

Flights: 1,369
Period: July 2025 to June 2026
Share of route: 33%
Carriers: 4

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

Alaska on SLC to SEA lands a B, about a point worse than the national rate of 77.6%. About one flight in four 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 1,369 flights. The strongest carrier on the route with a full sample, Delta Air Lines, flew 2,222 at 83.3% on time.

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

On time

76.7%

Arrivals under 15 minutes late, of 1,344 completed flights

Avg delay

46 min

Across delayed arrivals only, not all flights

Cancelled

1.83%

National rate is 1.81%

Whole route

80.2%

Every carrier on SLC to SEA, 4,108 flights

These figures cover 1,369 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 SLC to SEA

Alaska flew 1,369 of the 4,108 flights on SLC to SEA, about 33% of it. Its 76.7% on time is 4 points worse than the route as a whole, which runs 80.2%. Ranked by on-time rate it is number three of four carriers on the route, where the range runs from Delta at 83.3% to Frontier at 69.5%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.

The choice of carrier is not cosmetic here. Delta Air Lines arrives on time 83.3% of the time; SkyWest Airlines manages 77.3%. Sample sizes sit next to every figure, because a two-point gap across 419 flights means less than a ten-point one.

On-time performance by carrier on SLC to SEA
Airline	Flights	On time	Avg delay	Cancelled	Grade
Delta Air Lines	2,222	83.3%	54 min	0.54%	B+
SkyWest Airlines	419	77.3%	73 min	0.00%	B+
Alaska Airlines (this page)	1,369	76.7%	46 min	1.83%	B
Frontier Airlinesthin sample	98	69.5%	62 min	3.06%	C−

Delta leads SkyWest by 6 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.

Flight by flight

Alaska flight numbers on SLC to SEA

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 28 points, against 6 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am123 flights88.5%
8am–11am71 flights65.2%
11am–2pm362 flights86.6%
2pm–5pm438 flights73.3%
5pm–8pm173 flights79.0%
8pm–5am202 flights60.9%

Scale runs 50% to 95%. Rows with fewer than 30 flights show a dash.

The 8pm–5am window is where this operation falls apart: 60.9% on time, against 88.5% 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 2pm–5pm window is the busiest, with 438 flights scheduled in it.

Across the year

Alaska on SLC to SEA through the year

Darker means more delays. Figures are on-time percentages.April best, July worst

July is the worst month at 62.2% on time, 24 points below April, the best at 86.1%. 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. August was the busiest month here, with 135 flights.

Across the week, Tuesday is the strongest day at 81.3% on time and Thursday the weakest at 71.4%. 10 points is a smaller lever than departure hour, but it is free.

Delay causes

Why Alaska runs late on this route

One category carries most of the weight here. Late-arriving aircraft accounts for 44% of the 15,000 delay minutes carriers reported, and the remaining four split what is left. The split is by minutes rather than by flights, so a few very long delays count for as much as many short ones.

Late-arriving aircraft
44%
National Airspace System
30%
Carrier
19%
Extreme weather
6%
Security
0%

44% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. That is a cascade, and cascades start small and grow through the day. Across 15,000 reported delay minutes here, that single category outweighs weather by 7 to one. It is the strongest argument for booking the first departure of the morning, when the aircraft has been sitting at the gate overnight with nothing to inherit. The split is drawn from 14,514 reported delay minutes.

The practical consequence: the 5am–8am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 88.5% on time here.

Cancellations sit at 1.83% against a national 1.81%, which is ordinary. Diversions add another 0.00%.

Connections and stage length

What a delay here costs

Badly late arrivals are rare here: only 4.1% 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.

The 689 miles between these two airports put this in the middle of the US network, around two and a half to three hours of block time. That is enough cruise to absorb a ten-minute late pushback and not enough to absorb thirty. It is also long enough that the aircraft usually flies three or four legs a day rather than six, which slows how fast delay compounds.

The return leg runs 79.6% on time across 1,372 flights, within 3 points of this direction. The two legs are scored separately because they usually differ; on this city pair they happen not to.

The sample behind these figures is 1,369 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.

What to do with this

Booking Alaska on SLC to SEA

Put together: the calendar is the biggest lever here, not the carrier or the hour. April runs 86.1% on time and July 62.2%, a swing of 24 points. If the dates move at all, move them out of July before you think about anything else. 1,344 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