Flight number record
DL 1780
Delta Air Lines · Boston to San Juan
- Route
- BOS → SJU
- Departs
- 08:05
- Flights
- 365
- Period
- September 2025 to August 2026
Historical statistics for September 2025 to August 2026, not live status. For today’s DL 1780, check with Delta Air Lines.
DL 1780 lands a B, about a point worse than the national rate of 77.3%. About one flight in four arrives 15 minutes late or worse, and those flights are late by about 50 minutes on average. That rests on 365 flights, with a median arrival 4 minutes early.
Key figures
On time
76.5%
Arrivals under 15 minutes late, of 361 completed flights
Avg delay
51 min
Across delayed arrivals only, not all flights
Cancelled
1.10%
National rate is 1.89%
1 hour+ late
5.3%
National rate is 8.3%
These figures cover 365 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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Schedule
When DL 1780 flies
DL 1780 flies BOS to SJU without a single fixed slot. Its most common scheduled departure was 08:05, used on 99 of 365 flights, with 08:10 (90 flights) and 08:50 (90 flights) next.
- Departs 08:0599 flights27.1%
- Departs 08:1090 flights24.7%
- Departs 08:5090 flights24.7%
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 08:05 departure sits in the 8am–11am window. Across every US flight scheduled in that window the on-time rate is 83.9%, and DL 1780 runs 7 points worse at 76.5%. 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 1780 next to BOS to SJU
Every carrier on BOS to SJU combined arrived on time 66.8% of the time across 1,717 flights, so DL 1780 is 10 points ahead of it. Across its whole network Delta Air Lines managed 81.1%, which this flight trails by 5 points.
| Compared with | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| DL 1780 | 365 | 76.5% | 51 min | 1.10% | B |
| All Delta Air Lines on BOS–SJU | 398 | 74.5% | 57 min | 1.51% | C |
| All carriers on BOS–SJU | 1,717 | 66.8% | 76 min | 2.97% | C |
| Delta Air Lines, whole network | 1,039,517 | 81.1% | 71 min | 1.74% | B |
Across the year
DL 1780 quarter by quarter
DL 1780 did not run the same all year. Its best quarter was Apr–Jun 2026 at 82.4% on time and its weakest Jan–Mar 2026 at 69.8%, a swing of 13 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 flights70.0%
- Oct–Dec 202592 flights75.0%
- Jan–Mar 202690 flights69.8%
- Apr–Jun 202691 flights82.4%
- Jul–Sep 202662 flights82.3%
Scale runs 60% to 90%.
By weekday, DL 1780 did best on Friday at 82.7% on time and worst on Thursday at 69.2%. 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 1780 runs when it is late
The 85 late arrivals split 40 under half an hour, 26 between 30 and 60 minutes, and 19 an hour or more.
- 15+ min early79 flights21.9%
- Within 15 min197 flights54.6%
- 15–29 min late40 flights11.1%
- 30–59 min late26 flights7.2%
- 1–2 hours late13 flights3.6%
- 2+ hours late6 flights1.7%
Scale runs 0% to 100%.
Share of 361 completed flights by arrival against schedule.
16 of 63 late departures made up the time and arrived on time, 25% of them. In the other direction, 38 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 SJU.
The worst days
Worst days for DL 1780
The latest arrival of the period was on 24 February 2026, 6 hours 31 minutes behind schedule; most of its delay minutes were filed as a late-arriving aircraft. On three of the five worst days the largest share was filed as carrier-caused (crew, maintenance, fuelling, baggage).
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 24 February 2026 | 6 hours 31 minutes | Late-arriving aircraft |
| 7 September 2025 | 3 hours 49 minutes | Carrier |
| 27 January 2026 | 3 hours 41 minutes | Carrier |
| 27 December 2025 | 3 hours 34 minutes | Extreme weather |
| 3 June 2026 | 2 hours 45 minutes | Carrier |
Delay causes
Why DL 1780 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 4,299 reported delay minutes.
- 37%National Airspace System
- 36%Carrier
- 23%Late-arriving aircraft
- 4%Extreme weather
37% 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 1,570 minutes out of 4,299, against a national NAS share of 21%. The split is drawn from 4,299 delay minutes reported on DL 1780.
Cancellations sit at 1.10% against a national 1.89%, which is ordinary. Diversions add another 0.00%.
Connections and routes
What a delay on this flight costs
5.3% 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 1,674 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.
DL 1780 is not only a BOS to SJU flight. It also flew SJU to BOS (324 flights, 79.3% on time) often enough to be scored on its own. Airlines attach one number to several legs of an aircraft's day, and each leg keeps its own record here, so check which city pair is on your booking before reading a rate.
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.
| Also flown as | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| SJU to BOSthin sample | 324 | 79.3% | 58 min | 0.93% | B+ |
What to do with this
Booking DL 1780
For a booking, read DL 1780 as 76.5% on time with 1.10% 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 SJU, every carrier and departure
- SJU to BOS, the return direction
- JetBlue Airways 861 on the same route73.4%
- JetBlue Airways 561 on the same route48.5%
- Boston Logan International (BOS) delay statistics
- Luis Munoz Marin International (SJU) 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
- Worst months to fly in the US, ranked by the data
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.