Flight profile · United Airlines
UA2309
Denver (DEN) to San Diego (SAN) · scheduled 7:45 AM – 9:14 AM
How UA2309 performs
1,049 operations, July 2023 – July 2026.
UA2309 arrived on time 87.6% of the time, against 75.5% for all DEN → SAN flights, so this departure is 12.1 percentage points better than the route as a whole. Against United Airlines’ own flights on this route it is 7.5 points better.
Source: US DOT Bureau of Transportation Statistics · 1,049 operations, July 2023 – July 2026 · If UA2309 is cancelled or significantly changed, DOT’s automatic refund rule may entitle you to your money back. The refund checker walks through eligibility.
What stands out
How UA2309 compares to other flight numbers, not just to itself.
This flight runs unusually far ahead of the DEN → SAN route as a whole, better than 94% of 11,788 comparable flight numbers.
87.6% on time for this specific departure, against 75.5% for every DEN → SAN flight.
Source: FlyerIntel analysis of US DOT BTS data · July 2023 – July 2026 · The one thing about this specific departure that ranks most extreme against every other published flight number, out of everything FlyerIntel checks — shown only when something clears a real statistical bar, not for every flight.
Where UA2309 is right now
A live reading, only if you ask for it. It is not part of the reliability record above.
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Against the rest of the route
| Flight or route | On time | Cancelled | Median delay | Severe | Flights |
|---|---|---|---|---|---|
| UA2309 | 87.6% | 0.38% | -12 min | 3.3% | 1,049 |
| United Airlines on DEN → SAN | 80.1% | 0.85% | -7 min | 6.9% | 6,597 |
| All DEN → SAN flights | 75.5% | 0.98% | -4 min | 7.4% | 17,468 |
Source: FlyerIntel analysis of US DOT BTS data · July 2023 – July 2026
Why UA2309 runs late
Where US DOT attributed the delay minutes on this flight.
the inbound aircraft was late, so this flight started late
airspace and airport capacity, including weather-driven flow control
crew, maintenance, boarding and fueling, all within the carrier’s control
weather severe enough to stop this flight specifically
Share of the delay minutes US DOT attributed to each cause for UA2309 on DEN → SAN. Only delays of 15 minutes or more are attributed.
Source: US DOT Bureau of Transportation Statistics · Data covering July 2023 – July 2026
Does a late aircraft delay this flight?
How often the plane that flies UA2309 comes in late, and what that does to the departure.
UA2309 is usually the aircraft’s first flight of the day: the schedule gives it a median of 7.3 hours on the ground at DEN, so its “inbound” is mostly the aircraft’s arrival the evening before.
The aircraft flying UA2309 came in 15 or more minutes late on 10% of the departures where its previous flight is known. There are not enough departures in both groups to say how the flight left after a late one and after an on-time one.
Each departure is matched to the flight the same aircraft flew into DEN just before it, using the tail number in the DOT file, 781 of 1,045 departures in all. A departure is left out when that flight is unknown, was cancelled or diverted, or the aircraft had sat for more than 12 hours. A flight the airline cancelled never left and is not in the count, and one flown by a substitute aircraft is matched to the aircraft that flew it, not to the one first planned.
Against the network at the same turn length
| Share of departures | Inbound landed 15+ late |
|---|---|
| UA2309 | 10% |
| Network, same turn | 29% |
A night on the ground absorbs most of a late arrival, so a late inbound matters far less on a turn this long than on a same-day one.
The network row is every flight with a scheduled turn of 6 hours or more, usually overnight. How often UA2309’s aircraft landed 15 or more minutes late is lower than the network’s. There are not enough departures in both groups to compare how it left.
More: Which Flight Numbers Pay for a Late Aircraft lists the flight numbers that pass a late aircraft on.
Source: US DOT Bureau of Transportation Statistics · Data covering July 2023 – July 2026
From pushback to gate
When it leaves DEN late, does that still matter by the time it reaches SAN?
UA2309 pushes back an average of 1.1 minutes late and reaches the gate at SAN an average of 5.2 minutes early. The 6.3 minutes between those two figures are slack the published schedule already carries, which is why a late pushback on this flight does not reliably become a late arrival. Its 18.6 minutes on the taxiways at DEN is about what any departure from the airport in that hour spends.
On arrival at SAN, UA2309 spends 4.2 min taxiing from touchdown to the gate — ground time a connecting passenger sits through before they can even leave the aircraft, on top of however late the flight itself ran. That is 1.7 minutes shorter than a typical SAN arrival (6.0 min).
Departure delay is averaged over every pushback and arrival delay over every completed arrival, so the two counts differ by the flights that never reached SAN. Taxi-out is gate to wheels up and sits inside the scheduled block rather than on top of it; the comparison is 46,622 departures from DEN scheduled in the clock hour UA2309 most often leaves in. Taxi-in is landing to gate, compared against every arrival FlyerIntel has on file at SAN (297,664 flights), not just UA2309’s own. More on taxi time.
Source: FlyerIntel analysis of US DOT BTS data · July 2023 – July 2026
The hour it leaves DEN
Part of any flight’s record belongs to the clock rather than to the flight. UA2309 has one departure time, so this is what that time is worth.
On-time arrival rate. 46,622 departures from DEN are scheduled in the 7 AM–8 AM hour over the period, against 963,099 across the whole day.
UA2309 is scheduled out of DEN at 7:45 AM, in the 7 AM–8 AM bank. Departures from DEN in that hour arrive on time 87.5% of the time against 76.0% across the airport’s whole day — the slot alone is worth 11.5 points better before anything about this particular flight is considered.
The two airport figures cover every departure from DEN to every destination, so they describe the slot rather than this journey — the like-for-like comparison against the route is above. Hours are scheduled local, and a number whose schedule moved between banks inside the period has no single hour and is not described here at all. Why the hour matters.
Source: FlyerIntel analysis of US DOT BTS data · July 2023 – July 2026 · Hours below 120 departures are not scored.
By day of week
Does UA2309 run worse on particular days?
Tuesday is historically the most reliable day and Friday the least, a gap of 11.0 percentage points.
Source: FlyerIntel analysis of US DOT BTS data · July 2023 – July 2026 · Days with fewer than 120 operations are not scored.
Other routes UA2309 has flown
A flight number is a slot in a schedule, and carriers reassign it. These are the other city pairs this number served in the analysis period.
| Route | Operated | Flights | On time |
|---|---|---|---|
| SAN→SFO San Diego to San Francisco | February 15, 2024 – July 31, 2026 | 504 | 64.8% |
| MCI→DEN Kansas City to Denver | March 29, 2026 – April 5, 2026 | 3 | — |
| MSY→DEN New Orleans to Denver | December 19, 2024 – January 6, 2025 | 16 | — |
| SFO→PDX San Francisco to Portland | March 7, 2024 – December 18, 2024 | 267 | 85.0% |
| SAT→DEN San Antonio to Denver | October 27–31, 2024 | 5 | — |
| ORD→DEN Chicago to Denver | August 19–31, 2024 | 13 | — |
Because the same number has served different journeys, the statistics above describe only the route UA2309 currently operates. Blending them would produce an average of two different flights.
When it goes wrong
The average describes a usual day. This is the day that ruins a connection.
19 min late
against a median of 12 min early
Percentiles over 1,049 operations; cancelled and diverted flights are counted separately.
Source: US DOT Bureau of Transportation Statistics · Data covering July 2023 – July 2026
Other flights on this route
Same airports, same journey, different odds of arriving on time.
| Flight | Airline | On time | Median arrival | Operations |
|---|---|---|---|---|
| UA2309 this flight | United Airlines | 87.6% | 12 min early | 1,049 |
| UA1302 | United Airlines | 87.1% | 9 min early | 689 |
| F92817 | Frontier Airlines | 82.5% | 10 min early | 653 |
| UA1281 | United Airlines | 82.2% | 6 min early | 1,061 |
| F94989 | Frontier Airlines | 70.1% | 3 min early | 623 |
| UA540 | United Airlines | 68.9% | 0 min early | 1,039 |
Every departure listed carries at least 600 operations, so the comparison is between figures that mean something. UA2309 is placed in the same ordering rather than left out of it; the rows around it are the most punctual departures on the route, not all of them, so this is a comparison and not a rank. Schedules change; confirm the departure still operates before booking around this.
Data and methodology
Calculated by FlyerIntel from 1,049 records of UA2309 operating DEN → SAN, published by the US DOT Bureau of Transportation Statistics. A flight counts as delayed when it arrives 15 or more minutes after schedule. Cancelled and diverted flights are excluded from the on-time rate and reported separately. Flight numbers are resolved as carrier plus number plus route, because the same number serves different routes over time.
Full methodology · Data sources · Report a problem
Related research: Most and Least Reliable Flight Numbers · The Delay You Inherit · Making Up Time in the Air
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