Flight number record
DL 2639
Delta Air Lines · New York to Boston
- Route
- JFK → BOS
- Departs
- 21:00
- Flights
- 349
- Period
- September 2025 to August 2026
Historical statistics for September 2025 to August 2026, not live status. For today’s DL 2639, check with Delta Air Lines.
DL 2639 sits in the middle of the pack with a C−. About seven flights in ten arrive on time by the DOT's definition, 9 points worse than the national rate of 77.3%. The late ones land an hour and a half behind schedule. That rests on 349 flights, with a median arrival 4 minutes early.
The national on-time rate over the same period is 77.3%, so DL 2639 runs 9 points behind the country as a whole. Across a thousand flights that is about 91 extra late arrivals.
Key figures
On time
68.2%
Arrivals under 15 minutes late, of 336 completed flights
Avg delay
87 min
Across delayed arrivals only, not all flights
Cancelled
3.72%
National rate is 1.89%
1 hour+ late
16.4%
National rate is 8.3%
These figures cover 349 flights between September 2025 and August 2026. Beyond the headline rate, 16.4% of arrivals land a full hour or more behind schedule, against 8.3% nationally.
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Schedule
When DL 2639 flies
DL 2639 flies JFK to BOS without a single fixed slot. Its most common scheduled departure was 21:00, used on 143 of 349 flights, with 20:59 (64 flights) next.
- Departs 21:00143 flights41.0%
- Departs 20:5964 flights18.3%
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 21:00 departure sits in the 8pm–5am window. Across every US flight scheduled in that window the on-time rate is 70.1%, and DL 2639 runs level with that at 68.2%. By that time of day most aircraft have flown several legs already, and whatever went wrong earlier is still in the schedule.
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Against the route
DL 2639 next to JFK to BOS
Every carrier on JFK to BOS combined arrived on time 72.1% of the time across 5,615 flights, so DL 2639 is 4 points behind it. Across its whole network Delta Air Lines managed 81.1%, which this flight trails by 13 points.
| Compared with | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| DL 2639thin sample | 349 | 68.2% | 87 min | 3.72% | C− |
| All Delta Air Lines on JFK–BOS | 368 | 68.7% | 87 min | 3.53% | C− |
| All carriers on JFK–BOS | 5,615 | 72.1% | 79 min | 5.02% | C− |
| Delta Air Lines, whole network | 1,039,517 | 81.1% | 71 min | 1.74% | B |
Across the year
DL 2639 quarter by quarter
DL 2639 did not run the same all year. Its best quarter was Jan–Mar 2026 at 76.2% on time and its weakest Jul–Sep 2026 at 56.9%, a swing of 19 points on roughly 70 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 flights70.0%
- Oct–Dec 202580 flights65.8%
- Jan–Mar 202686 flights76.2%
- Apr–Jun 202691 flights69.7%
- Jul–Sep 202662 flights56.9%
Scale runs 50% to 80%.
By weekday, DL 2639 did best on Wednesday at 77.6% on time and worst on Monday at 60.4%. Each day rests on about 50 flights, so a gap of 17 points is worth noticing but could still narrow in another year.
Arrival by arrival
How late DL 2639 runs when it is late
DL 2639 often beats the schedule: 106 of 336 completed flights, 32%, arrived 15 minutes or more early. When DL 2639 is late it tends to be very late: 55 of its 107 late arrivals were an hour or more behind, and 21 were two hours or more.
- 15+ min early106 flights31.5%
- Within 15 min123 flights36.6%
- 15–29 min late26 flights7.7%
- 30–59 min late26 flights7.7%
- 1–2 hours late34 flights10.1%
- 2+ hours late21 flights6.3%
Scale runs 0% to 100%.
Share of 336 completed flights by arrival against schedule.
22 of 111 late departures made up the time and arrived on time, 20% of them. In the other direction, 18 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 BOS.
The worst days
Worst days for DL 2639
The latest arrival of the period was on 10 October 2025, 15 hours 54 minutes behind schedule; most of its delay minutes were filed as carrier-caused (crew, maintenance, fuelling, baggage). The same cause led on three of the five worst days.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 10 October 2025 | 15 hours 54 minutes | Carrier |
| 31 January 2026 | 12 hours 25 minutes | Carrier |
| 11 March 2026 | 5 hours | Late-arriving aircraft |
| 7 August 2026 | 4 hours 35 minutes | Late-arriving aircraft |
| 11 December 2025 | 3 hours 46 minutes | Carrier |
Delay causes
Why DL 2639 runs late
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 9,296 reported delay minutes.
- 42%Late-arriving aircraft
- 35%Carrier
- 23%National Airspace System
- 0%Extreme weather
42% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 9,296 reported delay minutes here, that single category outweighs weather by 42 to one. The split is drawn from 9,296 delay minutes reported on DL 2639.
Cancellations run at 3.72%, against 1.89% nationally. That is about one flight in 25 cancelled outright. A cancelled flight is invisible in every on-time figure on this page, so the punctuality numbers above describe only the flights that actually operated.
Connections and routes
What a delay on this flight costs
16.4% of arrivals land a full hour or more behind schedule, against 8.3% nationally. Ninety minutes is the honest minimum for a connection here, and two hours if the onward flight is on a separate ticket.
Every one of the 349 flights under DL 2639 in the data flew JFK to BOS. 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. 349 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 2639
For a booking, the cancellation rate is the figure to plan around on DL 2639: 3.72% of its 349 scheduled flights did not operate. A late arrival costs an hour and a half, but a cancellation costs the day, so leave a later option open.
Related
Where to go next
- JFK to BOS, every carrier and departure
- BOS to JFK, the return direction
- Republic Airways 5733 on the same route84.0%
- JetBlue Airways 1118 on the same route62.0%
- Republic Airways 5765 on the same route91.1%
- JetBlue Airways 618 on the same route56.0%
- Republic Airways 5798 on the same route60.8%
- JetBlue Airways 418 on the same route74.4%
- John F. Kennedy International (JFK) delay statistics
- Boston Logan International (BOS) 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
- Why the first flight of the morning is statistically safest
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.