Flight profile · United Airlines
UA688
Washington (IAD) to Boston (BOS) · scheduled 5:10 PM – 6:56 PM
How UA688 performs
1,036 operations, July 2023 – July 2026.
UA688 arrived on time 61.7% of the time, against 77.5% for all IAD → BOS flights, so this departure is 15.8 percentage points worse than the route as a whole. Against United Airlines’ own flights on this route it is 15.8 points worse.
Source: US DOT Bureau of Transportation Statistics · 1,036 operations, July 2023 – July 2026 · If UA688 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 UA688 compares to other flight numbers, not just to itself.
Which day you fly matters unusually much here, a wider weekday spread than 97% of 1,710 comparable flight numbers.
71.2% on time on a typical Saturday, against 50.3% on a Thursday.
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 UA688 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 |
|---|---|---|---|---|---|
| UA688 | 61.7% | 2.12% | 4 min | 18.4% | 1,036 |
| United Airlines on IAD → BOS | 77.5% | 1.53% | -5 min | 9.1% | 4,585 |
| All IAD → BOS flights | 77.5% | 1.68% | -5 min | 9.1% | 4,651 |
Source: FlyerIntel analysis of US DOT BTS data · July 2023 – July 2026
Why UA688 runs late
Where US DOT attributed the delay minutes on this flight.
airspace and airport capacity, including weather-driven flow control
the inbound aircraft was late, so this flight started late
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 UA688 on IAD → 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 UA688 comes in late, and what that does to the departure.
When the aircraft came in 15 or more minutes late, UA688 pushed back an average of 57 minutes late; when it came in on time or early, an average of 17 minutes late.
Each departure is matched to the flight the same aircraft flew into IAD just before it, using the tail number in the DOT file, 857 of 1,017 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 |
|---|---|---|---|
| UA688 | 15% | 63% | 23% |
| 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 UA688’s aircraft landed 15 or more minutes late is about the same as the network’s and, once the aircraft was late, how often UA688 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 July 2023 – July 2026
From pushback to gate
When it leaves IAD late, does that still matter by the time it reaches BOS?
On arrival at BOS, UA688 spends 6.8 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 2.1 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 37,767 departures from IAD scheduled in the clock hour UA688 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 UA688’s own. More on taxi time.
Source: FlyerIntel analysis of US DOT BTS data · July 2023 – July 2026
The hour it leaves IAD
Part of any flight’s record belongs to the clock rather than to the flight. UA688 has one departure time, so this is what that time is worth.
On-time arrival rate. 37,767 departures from IAD are scheduled in the 5 PM–6 PM hour over the period, against 170,208 across the whole day.
UA688 is scheduled out of IAD at 5:10 PM, in the 5 PM–6 PM bank. Departures from IAD in that hour arrive on time 72.1% of the time against 81.0% across the airport’s whole day — the slot alone is worth 8.9 points worse before anything about this particular flight is considered.
The two airport figures cover every departure from IAD 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 UA688 run worse on particular days?
Saturday is historically the most reliable day and Thursday the least, a gap of 20.9 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 UA688 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 |
|---|---|---|---|
| MCI→IAD Kansas City to Washington | June 25, 2026 – July 31, 2026 | 37 | — |
| SEA→IAD Seattle to Washington | May 21, 2026 – June 24, 2026 | 34 | — |
| LAS→IAD Las Vegas to Washington | March 29, 2026 – May 20, 2026 | 53 | — |
| SLC→IAD Salt Lake City to Washington | October 26, 2025 – February 11, 2026 | 74 | — |
| LAX→IAD Los Angeles to Washington | June 26, 2025 – January 5, 2026 | 118 | 84.2% |
| SFO→LAX San Francisco to Los Angeles | December 18, 2025 – January 5, 2026 | 19 | — |
| BOS→EWR Boston to Newark | September 29, 2023 – September 30, 2025 | 42 | — |
| MCO→IAD Orlando to Washington | May 22, 2025 – June 25, 2025 | 35 | — |
| BOS→DEN Boston to Denver | May 23, 2024 – May 21, 2025 | 75 | — |
| PHX→IAD Phoenix to Washington | February 13, 2025 – March 5, 2025 | 21 | — |
| RSW→IAD Fort Myers to Washington | August 19, 2024 – February 12, 2025 | 141 | 83.2% |
| EWR→BOS Newark to Boston | June 2–26, 2024 | 22 | — |
| AUS→IAD Austin to Washington | May 2–22, 2024 | 21 | — |
| SRQ→IAD Sarasota/Bradenton to Washington | January 9, 2024 – March 6, 2024 | 58 | — |
| TPA→IAD Tampa to Washington | September 29–30, 2023 | 2 | — |
| DEN→IAD Denver to Washington | August 1, 2023 – September 4, 2023 | 35 | — |
Because the same number has served different journeys, the statistics above describe only the route UA688 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.
99 min late
against a median of 4 min late
UA688 has an average that understates its risk: a typical arrival is 4 min late, but the worst tenth are 95 minutes worse than that. If the trip has something unmissable at the end of it, the median is the wrong number to plan against.
Percentiles over 1,036 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 |
|---|---|---|---|---|
| UA641 | United Airlines | 91.7% | 10 min early | 1,103 |
| UA755 | United Airlines | 79.5% | 4 min early | 600 |
| UA688 this flight | United Airlines | 61.7% | 4 min late | 1,036 |
Every departure listed carries at least 600 operations, so the comparison is between figures that mean something. UA688 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 1,036 records of UA688 operating IAD → 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
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