Flight number record
F9 4251
Frontier Airlines · Denver to Salt Lake City
- Route
- DEN → SLC
- Departs
- 22:29
- Flights
- 275
- Period
- September 2025 to August 2026
Historical statistics for September 2025 to August 2026, not live status. For today’s F9 4251, check with Frontier Airlines.
F9 4251 sits in the middle of the pack with a C+. About seven flights in ten arrive on time by the DOT's definition, 8 points worse than the national rate of 77.3%. The late ones land about an hour behind schedule. That rests on 275 flights, with a median arrival 3 minutes early.
The national on-time rate over the same period is 77.3%, so F9 4251 runs 8 points behind the country as a whole. Across a thousand flights that is about 76 extra late arrivals.
Key figures
On time
69.7%
Arrivals under 15 minutes late, of 274 completed flights
Avg delay
56 min
Across delayed arrivals only, not all flights
Cancelled
0.36%
National rate is 1.89%
1 hour+ late
10.2%
National rate is 8.3%
These figures cover 275 flights between September 2025 and August 2026. Beyond the headline rate, 10.2% of arrivals land a full hour or more behind schedule, against 8.3% nationally.
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Schedule
When F9 4251 flies
F9 4251 flies DEN to SLC without a single fixed slot. Its most common scheduled departure was 22:29, used on 142 of 275 flights, with 22:13 (44 flights) next.
- Departs 22:29142 flights51.6%
- Departs 22:1344 flights16.0%
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 22:29 departure sits in the 8pm–5am window. Across every US flight scheduled in that window the on-time rate is 70.1%, and F9 4251 runs level with that at 69.7%. By that time of day most aircraft have flown several legs already, and whatever went wrong earlier is still in the schedule.
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Against the route
F9 4251 next to DEN to SLC
Every carrier on DEN to SLC combined arrived on time 78.2% of the time across 7,713 flights, so F9 4251 is 9 points behind it. Frontier flew 1,033 flights on the same city pair under all its flight numbers, including this one, and those ran 81.9% on time. Across its whole network Frontier Airlines managed 72.7%, which this flight trails by 3 points.
| Compared with | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| F9 4251thin sample | 275 | 69.7% | 56 min | 0.36% | C+ |
| All Frontier Airlines on DEN–SLC | 1,033 | 81.9% | 57 min | 0.29% | B+ |
| All carriers on DEN–SLC | 7,713 | 78.2% | 61 min | 0.35% | B+ |
| Frontier Airlines, whole network | 213,022 | 72.7% | 84 min | 2.05% | C |
Across the year
F9 4251 quarter by quarter
F9 4251 did not run the same all year. Its best quarter was Apr–Jun 2026 at 78.5% on time and its weakest Jul–Sep 2026 at 59.0%, a swing of 20 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 202517 flights—
- Oct–Dec 202564 flights70.3%
- Jan–Mar 202667 flights71.6%
- Apr–Jun 202665 flights78.5%
- Jul–Sep 202662 flights59.0%
Scale runs 50% to 85%. Rows with fewer than 30 flights show a dash.
By weekday, F9 4251 did best on Saturday at 74.2% on time and worst on Sunday at 62.0%. Each day rests on about 39 flights, so a gap of 12 points is worth noticing but could still narrow in another year.
Arrival by arrival
How late F9 4251 runs when it is late
F9 4251 often beats the schedule: 81 of 274 completed flights, 30%, arrived 15 minutes or more early. The 83 late arrivals split 26 under half an hour, 29 between 30 and 60 minutes, and 28 an hour or more.
- 15+ min early81 flights29.6%
- Within 15 min110 flights40.1%
- 15–29 min late26 flights9.5%
- 30–59 min late29 flights10.6%
- 1–2 hours late18 flights6.6%
- 2+ hours late10 flights3.6%
Scale runs 0% to 100%.
Share of 274 completed flights by arrival against schedule.
17 of 88 late departures made up the time and arrived on time, 19% of them. 12 flights left on time and still arrived late.
The worst days
Worst days for F9 4251
The latest arrival of the period was on 10 August 2026, 3 hours 7 minutes behind schedule; most of its delay minutes were filed as a late-arriving aircraft. The same cause led on four of the five worst days.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 10 August 2026 | 3 hours 7 minutes | Late-arriving aircraft |
| 14 August 2026 | 3 hours | Late-arriving aircraft |
| 6 June 2026 | 2 hours 47 minutes | Late-arriving aircraft |
| 29 December 2025 | 2 hours 42 minutes | Carrier |
| 6 March 2026 | 2 hours 38 minutes | Late-arriving aircraft |
Delay causes
Why F9 4251 runs late
Late-arriving aircraft accounts for 51% of the 4,625 delay minutes carriers reported here, and the remaining four split what is left.
- 51%Late-arriving aircraft
- 32%Carrier
- 13%National Airspace System
- 4%Extreme weather
51% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 4,625 reported delay minutes here, that single category outweighs weather by 14 to one. The split is drawn from 4,625 delay minutes reported on F9 4251.
Cancellations are rare at 0.36%, 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
10.2% of arrivals land a full hour or more behind schedule, against 8.3% nationally. Ninety minutes is the honest minimum for a connection here, and two hours if the onward flight is on a separate ticket.
Every one of the 275 flights under F9 4251 in the data flew DEN 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. 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 F9 4251
For a booking, F9 4251 is one of the weaker ways to fly DEN to SLC: 9 points below the route as a whole. If the schedule allows, compare it with the other departures listed on the route page before settling on this one.
Related
Where to go next
- DEN to SLC, every carrier and departure
- SLC to DEN, the return direction
- United Airlines 1963 on the same route79.9%
- Delta Air Lines 2663 on the same route69.1%
- Delta Air Lines 1581 on the same route91.1%
- SkyWest Airlines 5762 on the same route71.3%
- Delta Air Lines 2544 on the same route88.2%
- Delta Air Lines 1623 on the same route81.4%
- Denver International (DEN) delay statistics
- Salt Lake City International (SLC) delay statistics
- Frontier Airlines on-time record
- Every Frontier Airlines 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 Frontier Airlines’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.