Flight number record
DL 384
Delta Air Lines · Boston to Seattle
- Route
- BOS → SEA
- Departs
- 07:15
- Flights
- 365
- Period
- September 2025 to August 2026
Historical statistics for September 2025 to August 2026, not live status. For today’s DL 384, check with Delta Air Lines.
DL 384 sits in the middle of the pack with a C. Close to three flights in four arrive on time by the DOT's definition, 3 points worse than the national rate of 77.3%. The late ones land roughly 45 minutes behind schedule. That rests on 365 flights, with a median arrival 2 minutes late.
Key figures
On time
74.3%
Arrivals under 15 minutes late, of 358 completed flights
Avg delay
47 min
Across delayed arrivals only, not all flights
Cancelled
1.64%
National rate is 1.89%
1 hour+ late
4.7%
National rate is 8.3%
These figures cover 365 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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Schedule
When DL 384 flies
DL 384 flies BOS to SEA without a single fixed slot. Its most common scheduled departure was 07:15, used on 119 of 365 flights, with 07:45 (55 flights) next.
- Departs 07:15119 flights32.6%
- Departs 07:4555 flights15.1%
Scale runs 0% to 100%.
Share of scheduled departures at each local time. Times used on fewer than one flight in ten are not listed.
A 07:15 departure sits in the 5am–8am window. Across every US flight scheduled in that window the on-time rate is 89.3%, and DL 384 runs 15 points worse at 74.3%. Early departures usually start with an aircraft that has not flown yet that day, which is most of why the window does well.
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Against the route
DL 384 next to BOS to SEA
Every carrier on BOS to SEA combined arrived on time 70.1% of the time across 2,555 flights, so DL 384 is 4 points ahead of it. Delta flew 1,068 flights on the same city pair under all its flight numbers, including this one, and those ran 71.1% on time. Across its whole network Delta Air Lines managed 81.1%, which this flight trails by 7 points.
| Compared with | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| DL 384 | 365 | 74.3% | 47 min | 1.64% | C |
| All Delta Air Lines on BOS–SEA | 1,068 | 71.1% | 57 min | 1.59% | C |
| All carriers on BOS–SEA | 2,555 | 70.1% | 55 min | 1.49% | C |
| Delta Air Lines, whole network | 1,039,517 | 81.1% | 71 min | 1.74% | B |
Across the year
DL 384 quarter by quarter
DL 384 did not run the same all year. Its best quarter was Jul–Sep 2025 at 86.7% on time and its weakest Jan–Mar 2026 at 57.0%, a swing of 30 points on roughly 73 flights a quarter. The twelve-month rate averages over that, so if you are flying in a weak quarter the quarter's own figure is the better guide.
- Jul–Sep 202530 flights86.7%
- Oct–Dec 202592 flights74.7%
- Jan–Mar 202690 flights57.0%
- Apr–Jun 202691 flights80.0%
- Jul–Sep 202662 flights83.6%
Scale runs 50% to 90%.
By weekday, DL 384 did best on Wednesday at 80.8% on time and worst on Tuesday at 66.7%. Each day rests on about 52 flights, so a gap of 14 points is worth noticing but could still narrow in another year.
Arrival by arrival
How late DL 384 runs when it is late
Most of the lateness is short. 53 of the 92 late arrivals were under half an hour behind, and 17 reached an hour or more.
- 15+ min early81 flights22.6%
- Within 15 min185 flights51.7%
- 15–29 min late53 flights14.8%
- 30–59 min late22 flights6.1%
- 1–2 hours late12 flights3.4%
- 2+ hours late5 flights1.4%
Scale runs 0% to 100%.
Share of 358 completed flights by arrival against schedule.
6 of 40 late departures made up the time and arrived on time, 15% of them. In the other direction, 58 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 DL 384
The latest arrival of the period was on 18 June 2026, 6 hours 59 minutes behind schedule; most of its delay minutes were filed as carrier-caused (crew, maintenance, fuelling, baggage). The five worst days are spread across June, August, July, January and September, with no single month standing out.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 18 June 2026 | 6 hours 59 minutes | Carrier |
| 3 August 2026 | 4 hours 53 minutes | National Airspace System |
| 21 July 2026 | 4 hours 51 minutes | National Airspace System |
| 27 January 2026 | 2 hours 16 minutes | Carrier |
| 7 September 2025 | 2 hours 2 minutes | Late-arriving aircraft |
Delay causes
Why DL 384 runs late
National Airspace System accounts for 56% of the 4,311 delay minutes carriers reported here, and the remaining four split what is left.
- 56%National Airspace System
- 30%Carrier
- 13%Late-arriving aircraft
- 1%Extreme weather
56% 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 2,396 minutes out of 4,311, against a national NAS share of 21%. The split is drawn from 4,311 delay minutes reported on DL 384.
Cancellations sit at 1.64% against a national 1.89%, which is ordinary. Diversions add another 0.27%.
Connections and routes
What a delay on this flight costs
Badly late arrivals are rare here: only 4.7% land an hour or more behind schedule, against 8.3% 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.
At 2,496 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.
Every one of the 365 flights under DL 384 in the data flew BOS to SEA. The number was not reused on any other city pair, which makes this a clean record of one route.
One caution: this is a thin sample. 365 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 DL 384
For a booking, read DL 384 as 74.3% on time with 1.64% cancelled over 365 flights. Those are rates from the past twelve months, not a forecast for any particular day.
Related
Where to go next
- BOS to SEA, every carrier and departure
- SEA to BOS, the return direction
- Alaska Airlines 459 on the same route72.3%
- Delta Air Lines 324 on the same route64.8%
- Boston Logan International (BOS) delay statistics
- Seattle-Tacoma International (SEA) delay statistics
- Delta Air Lines on-time record
- Every Delta Air Lines flight number with a record
- The most and least reliable flight numbers in the US
- The best time of day to fly, according to 7.05 million flight records
A flight number here means Delta Air Lines’s own number as it reports to the DOT. How the figures are computed is on the methodology page.
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.