Flight profile · United Airlines
UA2129
San Diego (SAN) to Washington (IAD) · scheduled 9:30 PM – 5:19 AM
How UA2129 performs
1,016 operations, September 2023 – July 2026.
UA2129 arrived on time 88.2% of the time, against 85.1% for all SAN → IAD flights, so this departure is 3.1 percentage points better than the route as a whole. Against United Airlines’ own flights on this route it is 1.6 points better.
Source: US DOT Bureau of Transportation Statistics · 1,016 operations, September 2023 – July 2026 · If UA2129 is cancelled or significantly changed, DOT’s automatic refund rule may entitle you to your money back. The refund checker walks through eligibility.
Where UA2129 is right now
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Against the rest of the route
| Flight or route | On time | Cancelled | Median delay | Severe | Flights |
|---|---|---|---|---|---|
| UA2129 | 88.2% | 1.38% | -13 min | 2.6% | 1,016 |
| United Airlines on SAN → IAD | 86.6% | 1.11% | -11 min | 3.9% | 3,610 |
| All SAN → IAD flights | 85.1% | 1.21% | -10 min | 4.1% | 4,729 |
Source: FlyerIntel analysis of US DOT BTS data · September 2023 – July 2026
Why UA2129 runs late
Where US DOT attributed the delay minutes on this flight.
crew, maintenance, boarding and fueling, all within the carrier’s control
the inbound aircraft was late, so this flight started late
weather severe enough to stop this flight specifically
airspace and airport capacity, including weather-driven flow control
Share of the delay minutes US DOT attributed to each cause for UA2129 on SAN → IAD. Only delays of 15 minutes or more are attributed.
Source: US DOT Bureau of Transportation Statistics · Data covering September 2023 – July 2026
Does a late aircraft delay this flight?
How often the plane that flies UA2129 comes in late, and what that does to the departure.
When the aircraft came in 15 or more minutes late, UA2129 pushed back an average of 38 minutes late; when it came in on time or early, an average of 0 minutes late.
Each departure is matched to the flight the same aircraft flew into SAN just before it, using the tail number in the DOT file, 1,000 of 1,002 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 | Left 15+ late after a late inbound | Left 15+ late after an on-time inbound |
|---|---|---|---|
| UA2129 | 18% | 45% | 5% |
| Network, same turn | 17% | 68% | 9% |
The schedule leaves a normal turn: enough time to clean and board if the aircraft is on time, little to spare if it is not.
The network row is every flight with a scheduled turn of 60 to 89 minutes. How often UA2129’s aircraft landed 15 or more minutes late is about the same as the network’s and, once the aircraft was late, how often UA2129 left 15 or more minutes late is lower than the network’s.
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 September 2023 – July 2026
From pushback to gate
When it leaves SAN late, does that still matter by the time it reaches IAD?
UA2129 pushes back an average of 7.7 minutes late and reaches the gate at IAD an average of 1.8 minutes early. The 9.5 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. It spends 21.1 minutes on the taxiways at SAN, 1.1 minutes longer than a typical SAN departure in the same hour.
On arrival at IAD, UA2129 spends 6.1 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 1.4 minutes shorter than a typical IAD arrival (7.5 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 IAD. Taxi-out is gate to wheels up and sits inside the scheduled block rather than on top of it; the comparison is 13,519 departures from SAN scheduled in the clock hour UA2129 most often leaves in. Taxi-in is landing to gate, compared against every arrival FlyerIntel has on file at IAD (169,930 flights), not just UA2129’s own. More on taxi time.
Source: FlyerIntel analysis of US DOT BTS data · September 2023 – July 2026
The hour it leaves SAN
Part of any flight’s record belongs to the clock rather than to the flight. UA2129 has one departure time, so this is what that time is worth.
On-time arrival rate. 13,519 departures from SAN are scheduled in the 9 PM–10 PM hour over the period, against 297,668 across the whole day.
UA2129 is scheduled out of SAN at 9:30 PM, in the 9 PM–10 PM bank. Departures from SAN in that hour arrive on time 75.5% of the time against 77.9% across the airport’s whole day, so the hour UA2129 leaves in is an ordinary one for SAN and explains nothing about its record either way.
The two airport figures cover every departure from SAN 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 · September 2023 – July 2026 · Hours below 120 departures are not scored.
By day of week
Does UA2129 run worse on particular days?
Saturday is historically the most reliable day and Friday the least, a gap of 8.7 percentage points.
Source: FlyerIntel analysis of US DOT BTS data · September 2023 – July 2026 · Days with fewer than 120 operations are not scored.
Other routes UA2129 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 |
|---|---|---|---|
| SFO→LAS San Francisco to Las Vegas | March 30, 2026 – April 27, 2026 | 5 | — |
| IAH→SAN Houston to San Diego | May 1–21, 2025 | 15 | — |
| SFO→SAN San Francisco to San Diego | July 1, 2023 – September 4, 2023 | 66 | — |
| SLC→SFO Salt Lake City to San Francisco | July 1, 2023 – September 4, 2023 | 66 | — |
Because the same number has served different journeys, the statistics above describe only the route UA2129 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 13 min early
Percentiles over 1,016 operations; cancelled and diverted flights are counted separately.
Source: US DOT Bureau of Transportation Statistics · Data covering September 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 |
|---|---|---|---|---|
| UA2129 this flight | United Airlines | 88.2% | 13 min early | 1,016 |
| AS322 | Alaska Airlines | 78.8% | 6 min early | 827 |
Every departure listed carries at least 600 operations, so the comparison is between figures that mean something. UA2129 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 1,016 records of UA2129 operating SAN → IAD, 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
Analysis last recomputed