Flight number record
DL 1171
Delta Air Lines · Detroit to Boston
- Route
- DTW → BOS
- Departs
- 14:00
- Flights
- 360
- Period
- September 2025 to August 2026
Historical statistics for September 2025 to August 2026, not live status. For today’s DL 1171, check with Delta Air Lines.
DL 1171 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 about an hour behind schedule. That rests on 360 flights, with a median arrival 1 minute late.
The national on-time rate over the same period is 77.3%, so DL 1171 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 355 completed flights
Avg delay
66 min
Across delayed arrivals only, not all flights
Cancelled
1.39%
National rate is 1.89%
1 hour+ late
11.3%
National rate is 8.3%
These figures cover 360 flights between September 2025 and August 2026. Beyond the headline rate, 11.3% of arrivals land a full hour or more behind schedule, against 8.3% nationally.
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Schedule
When DL 1171 flies
DL 1171 flies DTW to BOS without a single fixed slot. Its most common scheduled departure was 14:00, used on 105 of 360 flights, with 14:02 (38 flights) and 14:31 (36 flights) next.
- Departs 14:00105 flights29.2%
- Departs 14:0238 flights10.6%
- Departs 14:3136 flights10.0%
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 14:00 departure sits in the 2pm–5pm window. Across every US flight scheduled in that window the on-time rate is 71.9%, and DL 1171 runs 4 points worse at 68.2%. Midday slots inherit some of the morning's delays without yet carrying the full weight of the evening's.
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Against the route
DL 1171 next to DTW to BOS
Every carrier on DTW to BOS combined arrived on time 73.6% of the time across 2,572 flights, so DL 1171 is 5 points behind it. Delta flew 1,716 flights on the same city pair under all its flight numbers, including this one, and those ran 74.6% on time. 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 1171thin sample | 360 | 68.2% | 66 min | 1.39% | C |
| All Delta Air Lines on DTW–BOS | 1,716 | 74.6% | 65 min | 1.98% | C |
| All carriers on DTW–BOS | 2,572 | 73.6% | 71 min | 2.72% | C |
| Delta Air Lines, whole network | 1,039,517 | 81.1% | 71 min | 1.74% | B |
Across the year
DL 1171 quarter by quarter
DL 1171 did not run the same all year. Its best quarter was Jan–Mar 2026 at 75.9% on time and its weakest Jul–Sep 2025 at 46.7%, a swing of 29 points on roughly 72 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 flights46.7%
- Oct–Dec 202588 flights67.8%
- Jan–Mar 202689 flights75.9%
- Apr–Jun 202691 flights72.5%
- Jul–Sep 202662 flights61.7%
Scale runs 40% to 80%.
By weekday, DL 1171 did best on Saturday at 76.5% on time and worst on Sunday at 54.9%. Each day rests on about 51 flights, so a gap of 22 points is worth noticing but could still narrow in another year.
Arrival by arrival
How late DL 1171 runs when it is late
The 113 late arrivals split 36 under half an hour, 37 between 30 and 60 minutes, and 40 an hour or more.
- 15+ min early83 flights23.4%
- Within 15 min159 flights44.8%
- 15–29 min late36 flights10.1%
- 30–59 min late37 flights10.4%
- 1–2 hours late24 flights6.8%
- 2+ hours late16 flights4.5%
Scale runs 0% to 100%.
Share of 355 completed flights by arrival against schedule.
13 of 108 late departures made up the time and arrived on time, 12% 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 1171
The latest arrival of the period was on 26 January 2026, 5 hours 41 minutes behind schedule; most of its delay minutes were filed as national airspace system delay. The same cause led on four of the five worst days.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 26 January 2026 | 5 hours 41 minutes | National Airspace System |
| 14 October 2025 | 5 hours 2 minutes | National Airspace System |
| 24 September 2025 | 4 hours 24 minutes | National Airspace System |
| 24 January 2026 | 4 hours | Carrier |
| 25 September 2025 | 3 hours 53 minutes | National Airspace System |
Delay causes
Why DL 1171 runs late
National Airspace System accounts for 67% of the 7,427 delay minutes carriers reported here, and the remaining four split what is left.
- 67%National Airspace System
- 21%Carrier
- 12%Late-arriving aircraft
- 1%Extreme weather
67% 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 4,952 minutes out of 7,427, against a national NAS share of 21%. The split is drawn from 7,427 delay minutes reported on DL 1171.
Cancellations sit at 1.39% against a national 1.89%, which is ordinary. Diversions add another 0.00%.
Connections and routes
What a delay on this flight costs
11.3% 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.
The 632 miles between these two airports put this in the middle of the US network, around two and a half to three hours of block time. That is enough cruise to absorb a ten-minute late pushback and not enough to absorb thirty.
Every one of the 360 flights under DL 1171 in the data flew DTW 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. 360 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 1171
For a booking, DL 1171 is one of the weaker ways to fly DTW to BOS: 5 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
- DTW to BOS, every carrier and departure
- BOS to DTW, the return direction
- Delta Air Lines 1163 on the same route91.0%
- Delta Air Lines 2648 on the same route82.7%
- Delta Air Lines 1187 on the same route70.3%
- Delta Air Lines 1707 on the same route55.5%
- Detroit Metropolitan Wayne County (DTW) 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
- How often a connection fails at the major US hubs
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.