Flight Reliability
DL 1239 · Delta Air Lines
Seattle → Salt Lake City (SEA–SLC)
91
Nerd Approved
WanderNerd Reliability Score
- 84%
- Arrive within 15 minutes
- 0 min
- Average arrival delay
- 0.4%
- Cancelled
- 10 min early
- Median arrival delay
Based on 244 historical flights. Data through May 2026.
What the data says
Friday is doing you no favors.
DL 1239 arrived on time 92% of the time on Tuesdays and just 75% on Fridays. That gap is worth planning around.
A bit ahead of the Delta Air Lines network.
DL 1239 arrived on time 84% of the time, versus 81% across the Delta Air Lines network.
Slipping a little lately.
DL 1239 arrived on time 79% of the time over the last three months in the data, compared with 83% in the three months before that.
The breakdown
- Mon88%(48 flights)
- Tue92%(24 flights)
- Wed79%(24 flights)
- Thu87%(46 flights)
- Fri75%(44 flights)
- Sat80%(10 flights)
- Sun87%(47 flights)
69%
May
Jun 89% → May 69% on time
| Month | On-time percentage | Flights |
|---|---|---|
| June 2025 | 89% | 18 |
| July 2025 | 88% | 16 |
| August 2025 | 79% | 14 |
| September 2025 | 92% | 12 |
| October 2025 | 100% | 15 |
| November 2025 | 93% | 14 |
| December 2025 | 81% | 21 |
| January 2026 | 81% | 31 |
| February 2026 | 88% | 24 |
| March 2026 | 92% | 26 |
| April 2026 | 77% | 26 |
| May 2026 | 69% | 26 |
- Departures on time
- 84%
- Diverted
- 0%
- Flights flown
- 243
- Months covered
- 12
Same route, other flights
Keep nerding
Based on 244 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.