Flight Reliability
DL 399 · Delta Air Lines
Boston → Atlanta (BOS–ATL)98% of its flights flew this route. The rest (MCO–ATL) are included in these numbers.
- 69%
- Arrive within 15 minutes
- 15 min
- Average arrival delay
- 0.8%
- Cancelled
- 3 min early
- Median arrival delay
Based on 257 historical flights. Data through May 2026.
What the data says
Thursdays have been rough.
DL 399 arrived on time 78% of the time on Fridays and just 57% on Thursdays. That gap is worth planning around.
Lagging the BOS–ATL route.
DL 399 arrived on time 69% of the time, versus 79% across the BOS–ATL route.
Lagging the Delta Air Lines network.
DL 399 arrived on time 69% of the time, versus 81% across the Delta Air Lines network.
Ticking up lately.
DL 399 arrived on time 74% of the time over the last three months in the data, compared with 68% in the three months before that.
The breakdown
- Mon68%(37 flights)
- Tue68%(37 flights)
- Wed75%(36 flights)
- Thu57%(37 flights)
- Fri78%(36 flights)
- Sat69%(35 flights)
- Sun69%(35 flights)
- 9 AM–12 PM—(6 flights)
- 3–6 PM68%(247 flights)
Jun 57% → May 73% on time
| Month | On-time percentage | Flights |
|---|---|---|
| June 2025 | 57% | 30 |
| July 2025 | 67% | 30 |
| August 2025 | 73% | 30 |
| September 2025 | 67% | 30 |
| October 2025 | 61% | 31 |
| November 2025 | 77% | 30 |
| December 2025 | 78% | 18 |
| April 2026 | 71% | 24 |
| May 2026 | 73% | 30 |
- Departures on time
- 63%
- Diverted
- 0.8%
- Flights flown
- 253
- Months covered
- 9
Same route, other flights
Keep nerding
Based on 257 historical flights, because apparently we checked. Historical flight data: U.S. Bureau of Transportation Statistics, June 2025 – May 2026. Data through May 2026. How we calculate this.