Flight profile · United Airlines
UA1665
San Francisco (SFO) to Boston (BOS) · scheduled 11:25 PM – 8:08 AM
How UA1665 performs
1,045 operations, July 2023 – July 2026.
UA1665 arrived on time 81.8% of the time, against 77.9% for all SFO → BOS flights, so this departure is 3.9 percentage points better than the route as a whole. Against United Airlines’ own flights on this route it is 2.4 points better.
Source: US DOT Bureau of Transportation Statistics · 1,045 operations, July 2023 – July 2026 · If UA1665 is cancelled or significantly changed, DOT’s automatic refund rule may entitle you to your money back. The refund checker walks through eligibility.
Where UA1665 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 |
|---|---|---|---|---|---|
| UA1665 | 81.8% | 1.24% | -8 min | 4.8% | 1,045 |
| United Airlines on SFO → BOS | 79.4% | 1.01% | -8 min | 8.2% | 5,526 |
| All SFO → BOS flights | 77.9% | 1.04% | -7 min | 8.5% | 14,227 |
Source: FlyerIntel analysis of US DOT BTS data · July 2023 – July 2026
Why UA1665 runs late
Where US DOT attributed the delay minutes on this flight.
the inbound aircraft was late, so this flight started late
crew, maintenance, boarding and fueling, all within the carrier’s control
airspace and airport capacity, including weather-driven flow control
Share of the delay minutes US DOT attributed to each cause for UA1665 on SFO → BOS. 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 UA1665 comes in late, and what that does to the departure.
When the aircraft came in 15 or more minutes late, UA1665 pushed back an average of 22 minutes late; when it came in on time or early, an average of 1 minute late.
Each departure is matched to the flight the same aircraft flew into SFO just before it, using the tail number in the DOT file, 925 of 1,032 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 |
|---|---|---|---|
| UA1665 | 32% | 41% | 10% |
| Network, same turn | 23% | 40% | 9% |
The schedule leaves a long gap on the ground, which gives a late aircraft room to catch up before this flight pushes back.
The network row is every flight with a scheduled turn of 90 minutes to 3 hours. How often UA1665’s aircraft landed 15 or more minutes late is higher than the network’s and, once the aircraft was late, how often UA1665 left 15 or more minutes late is about the same as 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 July 2023 – July 2026
From pushback to gate
When it leaves SFO late, does that still matter by the time it reaches BOS?
UA1665 pushes back an average of 9.4 minutes late and reaches the gate at BOS an average of 2.1 minutes early. The 11.5 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 24.8 minutes on the taxiways at SFO, 2.5 minutes longer than a typical SFO departure in the same hour.
On arrival at BOS, UA1665 spends 6.7 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 2.2 minutes shorter than a typical BOS arrival (9.0 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 BOS. Taxi-out is gate to wheels up and sits inside the scheduled block rather than on top of it; the comparison is 19,618 departures from SFO scheduled in the clock hour UA1665 most often leaves in. Taxi-in is landing to gate, compared against every arrival FlyerIntel has on file at BOS (440,886 flights), not just UA1665’s own. More on taxi time.
Source: FlyerIntel analysis of US DOT BTS data · July 2023 – July 2026
The hour it leaves SFO
Part of any flight’s record belongs to the clock rather than to the flight. UA1665 has one departure time, so this is what that time is worth.
On-time arrival rate. 19,618 departures from SFO are scheduled in the 11 PM–12 AM hour over the period, against 435,779 across the whole day.
UA1665 is scheduled out of SFO at 11:25 PM, in the 11 PM–12 AM bank. Departures from SFO in that hour arrive on time 78.5% of the time against 78.7% across the airport’s whole day, so the hour UA1665 leaves in is an ordinary one for SFO and explains nothing about its record either way.
The two airport figures cover every departure from SFO 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 UA1665 run worse on particular days?
Tuesday is historically the most reliable day and Sunday the least, a gap of 12.8 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 UA1665 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 |
|---|---|---|---|
| ONT→SFO Ontario to San Francisco | March 5, 2026 – May 20, 2026 | 71 | — |
| ATL→SFO Atlanta to San Francisco | February 12, 2026 – March 4, 2026 | 18 | — |
| SEA→SFO Seattle to San Francisco | January 7, 2026 – February 11, 2026 | 24 | — |
| SBA→SFO Santa Barbara to San Francisco | December 18, 2025 – January 5, 2026 | 15 | — |
| MSY→SFO New Orleans to San Francisco | May 22, 2025 – October 25, 2025 | 157 | 73.7% |
| PHX→SFO Phoenix to San Francisco | March 6, 2025 – May 21, 2025 | 48 | — |
| SNA→SFO Santa Ana to San Francisco | December 19, 2024 – January 6, 2025 | 19 | — |
| IND→SFO Indianapolis to San Francisco | August 19, 2024 – December 2, 2024 | 61 | — |
Because the same number has served different journeys, the statistics above describe only the route UA1665 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.
33 min late
against a median of 8 min early
Percentiles over 1,045 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 |
|---|---|---|---|---|
| DL400 | Delta Air Lines | 90.4% | 13 min early | 784 |
| B6434 | JetBlue | 86.2% | 11 min early | 988 |
| AS356 | Alaska Airlines | 85.1% | 9 min early | 712 |
| UA2647 | United Airlines | 83.0% | 9 min early | 835 |
| UA1665 this flight | United Airlines | 81.8% | 8 min early | 1,045 |
| B6734 | JetBlue | 76.9% | 6 min early | 810 |
| B61734 | JetBlue | 74.9% | 6 min early | 1,055 |
| DL977 | Delta Air Lines | 71.6% | 4 min early | 829 |
Every departure listed carries at least 600 operations, so the comparison is between figures that mean something. UA1665 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 1,045 records of UA1665 operating SFO → BOS, 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