Flight number record
DL 571
Delta Air Lines · Boston to San Diego
- Route
- BOS → SAN
- Departs
- 17:10
- Flights
- 364
- Period
- September 2025 to August 2026
Historical statistics for September 2025 to August 2026, not live status. For today’s DL 571, check with Delta Air Lines.
DL 571 draws a C. About one flight in three arrives at least 15 minutes late, and the typical late arrival is roughly 45 minutes behind schedule. Build slack into anything you connect to. That rests on 364 flights, with a median arrival 1 minute late.
The national on-time rate over the same period is 77.3%, so DL 571 runs 11 points behind the country as a whole. Across a thousand flights that is about 113 extra late arrivals.
Key figures
On time
66.0%
Arrivals under 15 minutes late, of 353 completed flights
Avg delay
44 min
Across delayed arrivals only, not all flights
Cancelled
1.65%
National rate is 1.89%
1 hour+ late
7.6%
National rate is 8.3%
These figures cover 364 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 571 flies
DL 571 flies BOS to SAN without a single fixed slot. Its most common scheduled departure was 17:10, used on 100 of 364 flights, with 17:25 (74 flights) and 17:20 (45 flights) next.
- Departs 17:10100 flights27.5%
- Departs 17:2574 flights20.3%
- Departs 17:2045 flights12.4%
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 17:10 departure sits in the 5pm–8pm window. Across every US flight scheduled in that window the on-time rate is 68.0%, and DL 571 runs 2 points worse at 66.0%. 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 571 next to BOS to SAN
Every carrier on BOS to SAN combined arrived on time 75.3% of the time across 1,880 flights, so DL 571 is 9 points behind it. Across its whole network Delta Air Lines managed 81.1%, which this flight trails by 15 points.
| Compared with | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| DL 571thin sample | 364 | 66.0% | 44 min | 1.65% | C |
| All Delta Air Lines on BOS–SANthin sample | 364 | 66.0% | 44 min | 1.65% | C |
| All carriers on BOS–SAN | 1,880 | 75.3% | 62 min | 1.81% | B |
| Delta Air Lines, whole network | 1,039,517 | 81.1% | 71 min | 1.74% | B |
Across the year
DL 571 quarter by quarter
Quarter by quarter DL 571 held fairly steady: 66.7% in Oct–Dec 2025, 72.6% in Jan–Mar 2026, 65.9% in Apr–Jun 2026 and 62.9% in Jul–Sep 2026. A spread of 10 points is about what a sample of this size moves on its own, so the annual figure is a fair summary.
- Jul–Sep 202530 flights—
- Oct–Dec 202591 flights66.7%
- Jan–Mar 202690 flights72.6%
- Apr–Jun 202691 flights65.9%
- Jul–Sep 202662 flights62.9%
Scale runs 55% to 80%. Rows with fewer than 30 flights show a dash.
By weekday, DL 571 did best on Monday at 70.6% on time and worst on Friday at 57.7%. Each day rests on about 52 flights, so a gap of 13 points is worth noticing but could still narrow in another year.
Arrival by arrival
How late DL 571 runs when it is late
The 120 late arrivals split 56 under half an hour, 37 between 30 and 60 minutes, and 27 an hour or more.
- 15+ min early78 flights22.1%
- Within 15 min155 flights43.9%
- 15–29 min late56 flights15.9%
- 30–59 min late37 flights10.5%
- 1–2 hours late22 flights6.2%
- 2+ hours late5 flights1.4%
Scale runs 0% to 100%.
Share of 353 completed flights by arrival against schedule.
21 of 83 late departures made up the time and arrived on time, 25% 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 SAN.
The worst days
Worst days for DL 571
The latest arrival of the period was on 14 October 2025, 3 hours 18 minutes behind schedule; most of its delay minutes were filed as a late-arriving aircraft. The five worst days are spread across October, September, August, January and March, with no single month standing out.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 14 October 2025 | 3 hours 18 minutes | Late-arriving aircraft |
| 6 September 2025 | 2 hours 33 minutes | National Airspace System |
| 7 August 2026 | 2 hours 33 minutes | National Airspace System |
| 19 January 2026 | 2 hours 29 minutes | Carrier |
| 14 March 2026 | 2 hours 13 minutes | Late-arriving aircraft |
Delay causes
Why DL 571 runs late
National Airspace System accounts for 49% of the 5,219 delay minutes carriers reported here, and the remaining four split what is left.
- 49%National Airspace System
- 31%Late-arriving aircraft
- 20%Carrier
- 0%Extreme weather
49% 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 2,536 minutes out of 5,219, against a national NAS share of 21%. The split is drawn from 5,219 delay minutes reported on DL 571.
Cancellations sit at 1.65% against a national 1.89%, which is ordinary. Diversions add another 1.37%.
Connections and routes
What a delay on this flight costs
7.6% 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 roughly 45 minutes, which a normal layover absorbs.
At 2,588 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 same number turns up on one other city pair in the data, including SAN to BOS (162), but none flew often enough under DL 571 to report a rate for. Carriers move flight numbers between routes, so the figures on this page apply to BOS to SAN only.
One caution: this is a thin sample. 364 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 571
For a booking, DL 571 is one of the weaker ways to fly BOS to SAN: 9 points below the route as a whole. If the schedule allows, compare it with the other departures listed on the route page before settling on this one.
Related
Where to go next
- BOS to SAN, every carrier and departure
- SAN to BOS, the return direction
- Alaska Airlines 389 on the same route69.5%
- JetBlue Airways 619 on the same route87.2%
- Boston Logan International (BOS) delay statistics
- San Diego International (SAN) 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.