United Airlines is the most reliable airline on the IAD to SEA route with a 84% on-time rate, compared to Alaska Airlines at 79%. Based on 2,818 flights tracked.
Source: Bureau of Transportation Statistics. Updated October 2026.Best Airline: IAD to SEA
Washington to Seattle — airline reliability comparison
On-Time Rate by Airline
United Airlines84%
Delta Air Lines80%
Alaska Airlines79%
IAD to SEA Airline Comparison
| Airline | On-Time % | Cancel % | Avg Delay | Flights |
|---|---|---|---|---|
| United AirlinesUABest | 84% | 1.6% | 68m | 2,818 |
| Delta Air LinesDL | 80% | 1.0% | 115m | 1,675 |
| Alaska AirlinesASWorst | 79% | 1.1% | 53m | 3,010 |
Route Overview
81%
Overall On-Time
75m
Avg Delay
1.1%
Cancel Rate
7,503
Total Flights
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Data last updated October 2026. Source: Bureau of Transportation Statistics.