Flight number record

DL 1171

Delta Air Lines · Detroit to Boston

Route: DTW → BOS
Departs: 14:00
Flights: 360
Period: July 2025 to June 2026

Historical statistics for July 2025 to June 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, 8 points worse than the national rate of 77.6%. The late ones land a little over an hour behind schedule. That rests on 360 flights, with a median arrival right on schedule.

The national on-time rate over the same period is 77.6%, so DL 1171 runs 8 points behind the country as a whole. Across a thousand flights that is about 84 extra late arrivals.

On time

69.2%

Arrivals under 15 minutes late, of 357 completed flights

Avg delay

73 min

Across delayed arrivals only, not all flights

Cancelled

0.83%

National rate is 1.81%

1 hour+ late

12.6%

National rate is 8.1%

These figures cover 360 flights between July 2025 and June 2026. Beyond the headline rate, 12.6% of arrivals land a full hour or more behind schedule. That is the number that wrecks a connection, and it is not visible in an on-time percentage alone.

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 100 of 360 flights, with 14:03 (43 flights) and 14:31 (36 flights) next. Carriers retime flights through the season, so the rates here blend slightly different positions in the aircraft's day.

Departs 14:00100 flights27.8%
Departs 14:0343 flights11.9%
Departs 14:3136 flights10.0%

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 14:00 departure sits in the 2pm–5pm window. Across every US flight scheduled in that window the on-time rate is 72.4%, and DL 1171 runs 3 points worse at 69.2%. Midday slots inherit some of the morning's delays without yet carrying the full weight of the evening's.

Against the route

DL 1171 next to DTW to BOS

Every carrier on DTW to BOS combined arrived on time 74.8% of the time across 2,588 flights, so DL 1171 is 6 points behind it. Delta flew 1,710 flights on the same city pair under all its flight numbers, including this one, and those ran 74.9% on time. Across its whole network Delta Air Lines managed 81.6%, which this flight trails by 12 points.

DL 1171 against its route and carrier
Compared with	Flights	On time	Avg delay	Cancelled	Grade
DL 1171thin sample	360	69.2%	73 min	0.83%	C+
All Delta Air Lines on DTW–BOS	1,710	74.9%	67 min	1.81%	C
All carriers on DTW–BOS	2,588	74.8%	72 min	2.09%	C
Delta Air Lines, whole network	1,038,570	81.6%	71 min	1.62%	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 60.9%, a swing of 15 points on roughly 90 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 flights60.9%
Oct–Dec 202588 flights67.8%
Jan–Mar 202689 flights75.9%
Apr–Jun 202691 flights72.5%

Scale runs 50% to 80%. Rows with fewer than 30 flights show a dash.

By weekday, DL 1171 did best on Saturday at 76.9% 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.

Delay causes

Why DL 1171 runs late

One category carries most of the weight here. National Airspace System accounts for 63% of the 8,027 delay minutes carriers reported, and the remaining four split what is left. The split is by minutes rather than by flights, so a few very long delays count for as much as many short ones.

National Airspace System
63%
Carrier
18%
Late-arriving aircraft
15%
Extreme weather
4%

63% 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 5,059 minutes out of 8,027, against a national NAS share of 21%. The split is drawn from 8,027 delay minutes reported on DL 1171.

Cancellations are rare at 0.83%, below the national 1.81% and low enough to earn the plus on the grade. Roughly one flight in 100 is called off; the risk here is arriving late, not not arriving.

Connections and routes

What a delay on this flight costs

For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 12.6% of arrivals land a full hour or more behind schedule, against 8.1% nationally. A 45-minute layover does not survive that, and no amount of walking quickly changes it. Ninety minutes is the honest minimum 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. It is also long enough that the aircraft usually flies three or four legs a day rather than six, which slows how fast delay compounds.

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 a flight to put a long connection behind. 12.6% of its completed flights arrived an hour or more late, which a short layover will not absorb. If the onward flight is on a separate ticket, the risk sits with you.

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