Flight number record

DL 1780

Delta Air Lines · Boston to San Juan

Route: BOS → SJU
Departs: 08:10
Flights: 365
Period: July 2025 to June 2026

Historical statistics for July 2025 to June 2026, not live status. For today’s DL 1780, check with Delta Air Lines.

DL 1780 lands a B, level with the national rate of 77.6%. Roughly one flight in five arrives 15 minutes late or worse, and those flights are late by about 50 minutes on average. That is a workable record, not a spotless one. That rests on 365 flights, with a median arrival 4 minutes early.

On time

78.1%

Arrivals under 15 minutes late, of 361 completed flights

Avg delay

50 min

Across delayed arrivals only, not all flights

Cancelled

1.10%

National rate is 1.81%

1 hour+ late

4.4%

National rate is 8.1%

These figures cover 365 flights between July 2025 and June 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.

Schedule

When DL 1780 flies

DL 1780 flies BOS to SJU without a single fixed slot. Its most common scheduled departure was 08:10, used on 125 of 365 flights, with 08:05 (99 flights) and 08:50 (55 flights) next. Carriers retime flights through the season, so the rates here blend slightly different positions in the aircraft's day.

Departs 08:10125 flights34.2%
Departs 08:0599 flights27.1%
Departs 08:5055 flights15.1%

Scale runs 0% to 100%. Rows with fewer than 30 flights show a dash.

Share of scheduled departures at each local time. Times used on fewer than one flight in ten are not listed.

A 08:10 departure sits in the 8am–11am window. Across every US flight scheduled in that window the on-time rate is 84.1%, and DL 1780 runs 6 points worse at 78.1%. Early departures usually start with an aircraft that has not flown yet that day, which is most of why the window does well.

Against the route

DL 1780 next to BOS to SJU

Every carrier on BOS to SJU combined arrived on time 69.0% of the time across 1,819 flights, so DL 1780 is 9 points ahead of it. Across its whole network Delta Air Lines managed 81.6%, which this flight trails by 4 points.

DL 1780 against its route and carrier
Compared with	Flights	On time	Avg delay	Cancelled	Grade
DL 1780	365	78.1%	50 min	1.10%	B
All Delta Air Lines on BOS–SJU	398	76.0%	57 min	1.51%	B
All carriers on BOS–SJU	1,819	69.0%	74 min	2.69%	C
Delta Air Lines, whole network	1,038,570	81.6%	71 min	1.62%	B

Across the year

DL 1780 quarter by quarter

DL 1780 did not run the same all year. Its best quarter was Jul–Sep 2025 at 84.8% on time and its weakest Jan–Mar 2026 at 69.8%, a swing of 15 points on roughly 91 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 202592 flights84.8%
Oct–Dec 202592 flights75.0%
Jan–Mar 202690 flights69.8%
Apr–Jun 202691 flights82.4%

Scale runs 60% to 90%. Rows with fewer than 30 flights show a dash.

By weekday, DL 1780 ranged from 73.1% on Sunday to 82.7% on Friday. With about 52 flights behind each day, a spread of 10 points is inside normal variation, so the day you fly is not worth changing for this flight.

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 3,957 reported delay minutes.

Carrier
38%
National Airspace System
38%
Late-arriving aircraft
19%
Extreme weather
5%

38% 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 1,509 minutes out of 3,957, against a national NAS share of 21%. The split is drawn from 3,957 delay minutes reported on DL 1780.

Cancellations sit at 1.10% against a national 1.81%, which is ordinary. Diversions add another 0.00%.

Connections and routes

What a delay on this flight costs

Badly late arrivals are rare here: only 4.4% land an hour or more behind schedule, against 8.1% 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 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, 80.5% 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.

Other routes flown as DL 1780
Also flown as	Flights	On time	Avg delay	Cancelled	Grade
SJU to BOSthin sample	324	80.5%	58 min	0.93%	B+

What to do with this

Booking DL 1780

For a booking, read DL 1780 as 78.1% on time with 1.10% cancelled over 365 flights. Those are rates from the past twelve months, not a forecast for any particular day.

Where to go next

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, July 2025 to June 2026. Last updated 15 September 2026; recomputed monthly. How this data is collected.

Key figures