Flight number record
DL 638
Delta Air Lines · Boston to Atlanta
- Route
- BOS → ATL
- Departs
- 15:10
- Flights
- 275
- Period
- September 2025 to August 2026
Historical statistics for September 2025 to August 2026, not live status. For today’s DL 638, check with Delta Air Lines.
DL 638 lands a B+, level with the national rate of 77.3%. About one flight in four arrives 15 minutes late or worse, and those flights are late by a little over an hour on average. That rests on 275 flights, with a median arrival 6 minutes early.
Key figures
On time
76.6%
Arrivals under 15 minutes late, of 273 completed flights
Avg delay
74 min
Across delayed arrivals only, not all flights
Cancelled
0.73%
National rate is 1.89%
1 hour+ late
8.8%
National rate is 8.3%
These figures cover 275 flights between September 2025 and August 2026. Beyond the headline rate, 8.8% of arrivals land a full hour or more behind schedule, against 8.3% nationally.
Fare search by Aviasales, a Travelpayouts partner. Booking through it may earn this site a commission at no cost to you; it changes no figure here.
Schedule
When DL 638 flies
DL 638 flies BOS to ATL without a single fixed slot. Its most common scheduled departure was 15:10, used on 49 of 275 flights, with 15:00 (40 flights) and 15:20 (34 flights) next.
- Departs 15:1049 flights17.8%
- Departs 15:0040 flights14.5%
- Departs 15:2034 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 15:10 departure sits in the 2pm–5pm window. Across every US flight scheduled in that window the on-time rate is 71.9%, and DL 638 runs 5 points better at 76.6%. Midday slots inherit some of the morning's delays without yet carrying the full weight of the evening's.
Timetable by Aviasales, a Travelpayouts partner. Booking through it may earn this site a commission at no cost to you; it changes no figure here.
Against the route
DL 638 next to BOS to ATL
Every carrier on BOS to ATL combined arrived on time 76.8% of the time across 5,050 flights, so DL 638 is about level with it. Delta flew 3,726 flights on the same city pair under all its flight numbers, including this one, and those ran 80.8% on time. 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 638thin sample | 275 | 76.6% | 74 min | 0.73% | B+ |
| All Delta Air Lines on BOS–ATL | 3,726 | 80.8% | 75 min | 1.85% | B |
| All carriers on BOS–ATL | 5,050 | 76.8% | 72 min | 2.24% | B |
| Delta Air Lines, whole network | 1,039,517 | 81.1% | 71 min | 1.74% | B |
Across the year
DL 638 quarter by quarter
DL 638 did not run the same all year. Its best quarter was Apr–Jun 2026 at 91.4% on time and its weakest Jul–Sep 2026 at 64.9%, a swing of 27 points on roughly 69 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 flights70.3%
- Jan–Mar 202625 flights—
- Apr–Jun 202671 flights91.4%
- Jul–Sep 202657 flights64.9%
Scale runs 55% to 95%. Rows with fewer than 30 flights show a dash.
By weekday, DL 638 did best on Wednesday at 85.4% on time and worst on Monday at 69.2%. Each day rests on about 39 flights, so a gap of 16 points is worth noticing but could still narrow in another year.
Arrival by arrival
How late DL 638 runs when it is late
DL 638 often beats the schedule: 80 of 273 completed flights, 29%, arrived 15 minutes or more early. The 64 late arrivals split 25 under half an hour, 15 between 30 and 60 minutes, and 24 an hour or more.
- 15+ min early80 flights29.3%
- Within 15 min129 flights47.3%
- 15–29 min late25 flights9.2%
- 30–59 min late15 flights5.5%
- 1–2 hours late10 flights3.7%
- 2+ hours late14 flights5.1%
Scale runs 0% to 100%.
Share of 273 completed flights by arrival against schedule.
A late pushback is often recovered here: of 74 departures that left 15 minutes late or more, 25 still arrived on time. In the other direction, 15 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 ATL.
The worst days
Worst days for DL 638
The latest arrival of the period was on 7 December 2025, 5 hours 44 minutes behind schedule; most of its delay minutes were filed as a late-arriving aircraft. The five worst days are spread across December, June, November, September and March, with no single month standing out.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 7 December 2025 | 5 hours 44 minutes | Late-arriving aircraft |
| 22 June 2026 | 5 hours 23 minutes | Carrier |
| 8 November 2025 | 4 hours 31 minutes | National Airspace System |
| 6 September 2025 | 3 hours 42 minutes | National Airspace System |
| 16 March 2026 | 3 hours 34 minutes | Late-arriving aircraft |
Delay causes
Why DL 638 runs late
Late-arriving aircraft accounts for 44% of the 4,718 delay minutes carriers reported here, and the remaining four split what is left.
- 44%Late-arriving aircraft
- 32%National Airspace System
- 23%Carrier
- 0%Extreme weather
44% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 4,718 reported delay minutes here, that single category outweighs weather by 44 to one. The split is drawn from 4,718 delay minutes reported on DL 638.
Cancellations are rare at 0.73%, below the national 1.89% 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
8.8% 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 a little over an hour, which a normal layover absorbs.
The 946 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.
The same number turns up on two other city pairs in the data, including BUF to DTW (38) and EWR to SLC (6), but none flew often enough under DL 638 to report a rate for. Carriers move flight numbers between routes, so the figures on this page apply to BOS to ATL only.
One caution: this is a thin sample. 275 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 638
For a booking, read DL 638 as 76.6% on time with 0.73% cancelled over 275 flights. Those are rates from the past twelve months, not a forecast for any particular day.
Related
Where to go next
- BOS to ATL, every carrier and departure
- ATL to BOS, the return direction
- Delta Air Lines 695 on the same route86.0%
- Delta Air Lines 322 on the same route78.0%
- Delta Air Lines 973 on the same route79.1%
- Delta Air Lines 456 on the same route89.4%
- Delta Air Lines 385 on the same route86.4%
- Delta Air Lines 923 on the same route87.2%
- Boston Logan International (BOS) delay statistics
- Hartsfield-Jackson Atlanta International (ATL) 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
- Why the first flight of the morning is statistically safest
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.