Route reliability record
RDU→SEA
Raleigh to Seattle
- Flights
- 918
- Period
- September 2025 to August 2026
- Distance
- 2,354 mi
- Carriers
- 2
This route lands a B, level with the national rate of 77.3%. Roughly one flight in five arrives 15 minutes late or worse, and those flights are late by about 50 minutes on average. That rests on 918 RDU to SEA flights, with a median arrival 4 minutes early.
The US average over the same twelve months is 77.3%, so there is little to separate this route from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
78.0%
Arrivals under 15 minutes late, of 901 completed flights
Avg delay
51 min
Across delayed arrivals only, not all flights
Cancelled
1.20%
National rate is 1.89%
Best carrier
Alaska
74.9% on time across 554 flights
These figures cover 918 flights between September 2025 and August 2026. The median arrival is 4 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.
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Carrier by carrier
Which airline is most reliable on RDU to SEA
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.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Delta Air Linesthin sample | 364 | 82.8% | 49 min | 1.37% | B |
| Alaska Airlines | 554 | 74.9% | 52 min | 1.08% | C |
Flight by flight
Flights on RDU to SEA
The flight numbers below flew this route at least 250 times in the period, busiest first. Each has its own record, with its schedule and delay causes.
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Departure window
The best time of day to leave
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 918 flights.
- 5am–8am588 flights81.5%
- 8am–11am—
- 11am–2pm—
- 2pm–5pm—
- 5pm–8pm330 flights71.8%
- 8pm–5am—
Scale runs 65% to 85%. Rows with fewer than 30 flights show a dash.
Book the early departure. Flights leaving between 5am–8am arrive on time 81.5% of the time, against 71.8% for the evening window. That is 10 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 5am–8am window is the busiest, with 588 flights scheduled in it.
Explore
Filter RDU to SEA by airline, time, month and day
Pick a breakdown and a carrier. The dashed mark on each row is the same slice for every US flight.
On RDU to SEA, the best departure window is 5am–8am at 81.5% on time and the worst is 5pm–8pm at 71.8%, a real gap of 9.7 points. All US flights leaving 5am–8am ran 89.3%.
- 5–8am81.5%
- 8–11am—
- 11am–2pm—
- 2–5pm—
- 5–8pm71.8%
- 8pm–5am—
best all US flightsScale 60% to 95%. Cells under 30 flights show a dash.
Across the year
When delays peak on this route
This route's year swings by 45 points from best month to worst, which is wide. An annual average tells you very little about the week you are actually flying, so read the strip rather than the headline if your dates are fixed.
December is the weak month at 47.9% on time, against 93.3% 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. May was the busiest month here, with 93 flights.
Across the week, Saturday is the strongest day at 82.1% on time and Monday the weakest at 69.3%, a spread of 13 points.
Delay causes
Why this route gets delayed
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 10,000 reported delay minutes.
- 37%Carrier
- 34%National Airspace System
- 27%Late-arriving aircraft
- 1%Extreme weather
- 1%Security
The largest share of delay minutes, 37%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 3,736 of the 10,000 delay minutes reported here. The split is drawn from 10,056 reported delay minutes.
34% 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 3,416 minutes out of 10,000, against a national NAS share of 21%.
Cancellations sit at 1.20% against a national 1.89%, which is ordinary. Diversions add another 0.65%.
Connections and stage length
What a delay here actually costs
5.0% 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 about 50 minutes, which a normal layover absorbs.
At 2,354 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 81.4% on time across 918 flights, 3 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 3 points of difference.
One caution: this is a thin sample. 918 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.
Work out the risk of missing a connection in SEA after this flight
What to do with this
Booking this route
Put together: treat all of this as provisional. 918 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 78.0% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 901 completed flights over 12 months sit behind that.
Common questions
RDU to SEA questions
How often is RDU to SEA delayed?
Roughly one flight in five arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 22.0% of the 918 flights in this analysis, against 22.7% nationally. Delayed flights are late by about 50 minutes on average.
How reliable is RDU to SEA compared with the rest of the country?
78.0% of flights arrive on time here against a national 77.3%, a difference of half a point in its favour. That is worth a B on this site's grading scale.
What time of day has the fewest delays on RDU to SEA?
The 5am–8am departure window is the strongest at 81.5% on time. The 5pm–8pm window is the weakest at 71.8%, 10 points behind. Later departures inherit delays from earlier flights the same aircraft has already flown, which is why the curve slopes the way it does.
How bad are December delays on RDU to SEA?
December is the weakest month at 47.9% on time, compared with 93.3% in September. Across the year that is 45 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.
Related
Where to go next
- SEA to RDU — the return legseparate record
- Raleigh-Durham International (RDU) delay statistics
- Seattle-Tacoma International (SEA) delay statistics
- Delta Air Lines on RDU to SEA82.8%
- Alaska Airlines on RDU to SEA74.9%
- RDU to ATL, a related route86.5%
- LAX to SEA, a related route85.0%
- RDU to ORD, a related route74.3%
- Delta Air Lines on-time record82.8%
- Alaska Airlines on-time record74.9%
- The best time of day to fly, according to 7.05 million flight records
- Worst months to fly in the US, ranked by the data
Direction matters. RDU to SEA and SEA to RDU are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.
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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.