Flight number record
DL 1128
Delta Air Lines · Seattle to Salt Lake City
- Route
- SEA → SLC
- Departs
- 05:30
- Flights
- 365
- Period
- September 2025 to August 2026
Historical statistics for September 2025 to August 2026, not live status. For today’s DL 1128, check with Delta Air Lines.
DL 1128 earns an A+. Nearly every flight arrives inside the 15-minute window the DOT uses to define an on-time arrival, which puts it 16 points better than the national rate of 77.3%. When something does go wrong the average delay runs a little over an hour. That rests on 365 flights, with a median arrival 14 minutes early.
Set against the rest of the country, DL 1128's record is 16 points better than the US average of 77.3%. That gap is worth roughly 164 fewer late arrivals for every thousand flights.
Key figures
On time
93.7%
Arrivals under 15 minutes late, of 363 completed flights
Avg delay
71 min
Across delayed arrivals only, not all flights
Cancelled
0.55%
National rate is 1.89%
1 hour+ late
2.2%
National rate is 8.3%
These figures cover 365 flights between September 2025 and August 2026. The median arrival is 14 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.
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Schedule
When DL 1128 flies
DL 1128 flies SEA to SLC without a single fixed slot. Its most common scheduled departure was 05:30, used on 195 of 365 flights, with 05:25 (101 flights) next.
- Departs 05:30195 flights53.4%
- Departs 05:25101 flights27.7%
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 05:30 departure sits in the 5am–8am window. Across every US flight scheduled in that window the on-time rate is 89.3%, and DL 1128 runs 4 points better at 93.7%. Early departures usually start with an aircraft that has not flown yet that day, which is most of why the window does well.
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Against the route
DL 1128 next to SEA to SLC
Every carrier on SEA to SLC combined arrived on time 83.4% of the time across 4,098 flights, so DL 1128 is 10 points ahead of it. Delta flew 2,232 flights on the same city pair under all its flight numbers, including this one, and those ran 86.8% on time. Across its whole network Delta Air Lines managed 81.1%, which this flight beats by 13 points.
| Compared with | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| DL 1128 | 365 | 93.7% | 71 min | 0.55% | A+ |
| All Delta Air Lines on SEA–SLC | 2,232 | 86.8% | 59 min | 0.49% | A+ |
| All carriers on SEA–SLC | 4,098 | 83.4% | 49 min | 0.78% | B+ |
| Delta Air Lines, whole network | 1,039,517 | 81.1% | 71 min | 1.74% | B |
Across the year
DL 1128 quarter by quarter
DL 1128 did not run the same all year. Its best quarter was Apr–Jun 2026 at 98.9% on time and its weakest Jan–Mar 2026 at 85.4%, a swing of 14 points on roughly 73 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 flights93.3%
- Oct–Dec 202592 flights95.7%
- Jan–Mar 202690 flights85.4%
- Apr–Jun 202691 flights98.9%
- Jul–Sep 202662 flights95.1%
Scale runs 75% to 100%.
By weekday, DL 1128 ranged from 90.4% on Saturday to 96.2% on Friday. With about 52 flights behind each day, a spread of 6 points is inside normal variation, so the day you fly is not worth changing for this flight.
Arrival by arrival
How late DL 1128 runs when it is late
DL 1128 often beats the schedule: 179 of 363 completed flights, 49%, arrived 15 minutes or more early. The 23 late arrivals split 10 under half an hour, 5 between 30 and 60 minutes, and 8 an hour or more.
- 15+ min early179 flights49.3%
- Within 15 min161 flights44.4%
- 15–29 min late10 flights2.8%
- 30–59 min late5 flights1.4%
- 1–2 hours late2 flights0.6%
- 2+ hours late6 flights1.7%
Scale runs 0% to 100%.
Share of 363 completed flights by arrival against schedule.
3 of 21 late departures made up the time and arrived on time, 14% of them. Only 5 left on time and still arrived late.
The worst days
Worst days for DL 1128
The latest arrival of the period was on 25 October 2025, 3 hours 38 minutes behind schedule; most of its delay minutes were filed as carrier-caused (crew, maintenance, fuelling, baggage). The same cause led on five of the five worst days.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 25 October 2025 | 3 hours 38 minutes | Carrier |
| 10 October 2025 | 3 hours 28 minutes | Carrier |
| 12 March 2026 | 3 hours 7 minutes | Carrier |
| 6 September 2025 | 2 hours 41 minutes | Carrier |
| 28 March 2026 | 2 hours 30 minutes | Carrier |
Delay causes
Why DL 1128 runs late
Carrier accounts for 88% of the 1,636 delay minutes carriers reported here, and the remaining four split what is left.
- 88%Carrier
- 12%National Airspace System
The largest share of delay minutes, 88%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 1,447 of the 1,636 delay minutes reported here. The split is drawn from 1,636 delay minutes reported on DL 1128.
Cancellations are rare at 0.55%, 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
Badly late arrivals are rare here: only 2.2% land an hour or more behind schedule, against 8.3% nationally. Connections built on this flight are about as safe as US domestic connections get, though a cancelled flight still ignores every layover you give it.
The 689 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.
Every one of the 365 flights under DL 1128 in the data flew SEA to SLC. 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. 365 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 1128
For a booking, DL 1128 has one of the better records a US domestic flight can show: 93.7% on time and 0.55% cancelled. That is a base rate, not a promise about any single day.
Related
Where to go next
- SEA to SLC, every carrier and departure
- SLC to SEA, the return direction
- Delta Air Lines 1016 on the same route90.0%
- Delta Air Lines 1120 on the same route83.0%
- Delta Air Lines 1265 on the same route85.1%
- Delta Air Lines 1165 on the same route80.4%
- SkyWest Airlines 3298 on the same route79.3%
- Alaska Airlines 733 on the same route68.4%
- Seattle-Tacoma International (SEA) delay statistics
- Salt Lake City International (SLC) 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
- Worst months to fly in the US, ranked by the data
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.