Flight number record
DL 638
Delta Air Lines · Boston to Atlanta
- Route
- BOS → ATL
- Departs
- 15:10
- Flights
- 280
- Period
- July 2025 to June 2026
Historical statistics for July 2025 to June 2026, not live status. For today’s DL 638, check with Delta Air Lines.
DL 638 lands a B, about a point better than the national rate of 77.6%. About one flight in five arrives 15 minutes late or worse, and those flights are late by about an hour on average. That is a workable record, not a spotless one. That rests on 280 flights, with a median arrival 5 minutes early.
Key figures
On time
78.5%
Arrivals under 15 minutes late, of 274 completed flights
Avg delay
66 min
Across delayed arrivals only, not all flights
Cancelled
1.43%
National rate is 1.81%
1 hour+ late
6.6%
National rate is 8.1%
These figures cover 280 flights between July 2025 and June 2026. The median arrival is 5 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 638 flies
DL 638 flies BOS to ATL without a single fixed slot. Its most common scheduled departure was 15:10, used on 56 of 280 flights, with 15:00 (40 flights) and 15:20 (34 flights) next. Carriers retime flights through the season, so the rates here blend slightly different positions in the aircraft's day.
- Departs 15:1056 flights20.0%
- Departs 15:0040 flights14.3%
- Departs 15:2034 flights12.1%
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 15:10 departure sits in the 2pm–5pm window. Across every US flight scheduled in that window the on-time rate is 72.4%, and DL 638 runs 6 points better at 78.5%. Midday slots inherit some of the morning's delays without yet carrying the full weight of the evening's.
Against the route
DL 638 next to BOS to ATL
Every carrier on BOS to ATL combined arrived on time 78.5% of the time across 4,931 flights, so DL 638 is about level with it. Delta flew 3,662 flights on the same city pair under all its flight numbers, including this one, and those ran 82.1% on time. Across its whole network Delta Air Lines managed 81.6%, which this flight trails by 3 points.
| Compared with | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| DL 638thin sample | 280 | 78.5% | 66 min | 1.43% | B |
| All Delta Air Lines on BOS–ATL | 3,662 | 82.1% | 75 min | 1.77% | B |
| All carriers on BOS–ATL | 4,931 | 78.5% | 69 min | 1.99% | B |
| Delta Air Lines, whole network | 1,038,570 | 81.6% | 71 min | 1.62% | 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 Oct–Dec 2025 at 70.3%, a swing of 21 points on roughly 93 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 flights72.7%
- Oct–Dec 202592 flights70.3%
- Jan–Mar 202625 flights—
- Apr–Jun 202671 flights91.4%
Scale runs 60% to 95%. Rows with fewer than 30 flights show a dash.
By weekday, DL 638 did best on Wednesday at 88.1% on time and worst on Monday at 69.2%. Each day rests on about 40 flights, so a gap of 19 points is worth noticing but could still narrow in another year.
Delay causes
Why DL 638 runs late
One category carries most of the weight here. Late-arriving aircraft accounts for 52% of the 3,909 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.
- 52%Late-arriving aircraft
- 24%National Airspace System
- 23%Carrier
- 1%Extreme weather
52% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. That is a cascade, and cascades start small and grow through the day. Across 3,909 reported delay minutes here, that single category outweighs weather by 52 to one. It is the strongest argument for booking the first departure of the morning, when the aircraft has been sitting at the gate overnight with nothing to inherit. The split is drawn from 3,909 delay minutes reported on DL 638.
Cancellations sit at 1.43% against a national 1.81%, which is ordinary. Diversions add another 0.71%.
Connections and routes
What a delay on this flight costs
6.6% of arrivals land an hour or more late, close to the national 8.1%. That is the figure that decides a connection, and it says a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route last about 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. 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.
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. 280 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 78.5% on time with 1.43% cancelled over 280 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 973 on the same route84.5%
- Delta Air Lines 695 on the same route87.4%
- Delta Air Lines 322 on the same route82.0%
- Delta Air Lines 456 on the same route88.9%
- Delta Air Lines 385 on the same route88.4%
- Delta Air Lines 923 on the same route87.3%
- 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, July 2025 to June 2026. Last updated 15 September 2026; recomputed monthly. How this data is collected.