Flight number record

F9 4251

Frontier Airlines · Denver to Salt Lake City

Route: DEN → SLC
Departs: 22:29
Flights: 255
Period: July 2025 to June 2026

Historical statistics for July 2025 to June 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 77.6%. The late ones land about an hour behind schedule. That rests on 255 flights, with a median arrival 3 minutes early.

The national on-time rate over the same period is 77.6%, so F9 4251 runs 8 points behind the country as a whole. Across a thousand flights that is about 84 extra late arrivals.

On time

69.2%

Arrivals under 15 minutes late, of 253 completed flights

Avg delay

57 min

Across delayed arrivals only, not all flights

Cancelled

0.78%

National rate is 1.81%

1 hour+ late

10.7%

National rate is 8.1%

These figures cover 255 flights between July 2025 and June 2026. Beyond the headline rate, 10.7% of arrivals land a full hour or more behind schedule. That is the number that wrecks a connection, and it is not visible in an on-time percentage alone.

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 156 of 255 flights, with 22:44 (28 flights) next. Carriers retime flights through the season, so the rates here blend slightly different positions in the aircraft's day.

Departs 22:29156 flights61.2%
Departs 22:4428 flights11.0%

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 22:29 departure sits in the 8pm–5am window. Across every US flight scheduled in that window the on-time rate is 70.5%, and F9 4251 runs level with that at 69.2%. By that time of day most aircraft have flown several legs already, and whatever went wrong earlier is still in the schedule.

Against the route

F9 4251 next to DEN to SLC

Every carrier on DEN to SLC combined arrived on time 77.5% of the time across 7,758 flights, so F9 4251 is 8 points behind it. Frontier flew 1,010 flights on the same city pair under all its flight numbers, including this one, and those ran 81.7% on time. Across its whole network Frontier Airlines managed 73.2%, which this flight trails by 4 points.

F9 4251 against its route and carrier
Compared with	Flights	On time	Avg delay	Cancelled	Grade
F9 4251thin sample	255	69.2%	57 min	0.78%	C+
All Frontier Airlines on DEN–SLC	1,010	81.7%	60 min	0.50%	B+
All carriers on DEN–SLC	7,758	77.5%	61 min	0.48%	B+
Frontier Airlines, whole network	205,332	73.2%	84 min	1.85%	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 2025 at 54.4%, a swing of 24 points on roughly 64 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 202559 flights54.4%
Oct–Dec 202564 flights70.3%
Jan–Mar 202667 flights71.6%
Apr–Jun 202665 flights78.5%

Scale runs 45% to 85%. Rows with fewer than 30 flights show a dash.

By weekday, F9 4251 did best on Monday at 73.5% on time and worst on Sunday at 56.0%. Each day rests on about 36 flights, so a gap of 18 points is worth noticing but could still narrow in another year.

Delay causes

Why F9 4251 runs late

One category carries most of the weight here. Late-arriving aircraft accounts for 51% of the 4,478 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.

Late-arriving aircraft
51%
Carrier
36%
National Airspace System
11%
Extreme weather
2%

51% 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 4,478 reported delay minutes here, that single category outweighs weather by 25 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 4,478 delay minutes reported on F9 4251.

Cancellations are rare at 0.78%, below the national 1.81% 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

For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 10.7% of arrivals land a full hour or more behind schedule, against 8.1% nationally. A 45-minute layover does not survive that, and no amount of walking quickly changes it. Ninety minutes is the honest minimum here, and two hours if the onward flight is on a separate ticket.

Every one of the 255 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. 255 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: 8 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.

Where to go next

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, July 2025 to June 2026. Last updated 15 September 2026; recomputed monthly. How this data is collected.

Key figures