Flight number record
UA 637
United Airlines · Washington to Austin
- Route
- IAD → AUS
- Departs
- 08:25
- Flights
- 254
- Period
- September 2025 to August 2026
Historical statistics for September 2025 to August 2026, not live status. For today’s UA 637, check with United Airlines.
UA 637 earns an A+. Close to nine flights in ten arrive inside the 15-minute window the DOT uses to define an on-time arrival, which puts it 15 points better than the national rate of 77.3%. When something does go wrong the average delay runs about an hour. That rests on 254 flights, with a median arrival 17 minutes early.
Set against the rest of the country, UA 637's record is 15 points better than the US average of 77.3%. That gap is worth roughly 152 fewer late arrivals for every thousand flights.
Key figures
On time
92.5%
Arrivals under 15 minutes late, of 252 completed flights
Avg delay
61 min
Across delayed arrivals only, not all flights
Cancelled
0.79%
National rate is 1.89%
1 hour+ late
2.8%
National rate is 8.3%
These figures cover 254 flights between September 2025 and August 2026. The median arrival is 17 minutes early, which is the part an average hides: most flights here are fine, and the on-time rate is decided by a tail of badly late ones. On-time means under 15 minutes late, the DOT's own threshold.
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Schedule
When UA 637 flies
UA 637 flies IAD to AUS without a single fixed slot. Its most common scheduled departure was 08:25, used on 70 of 254 flights, with 08:30 (61 flights) and 08:15 (39 flights) next.
- Departs 08:2570 flights27.6%
- Departs 08:3061 flights24.0%
- Departs 08:1539 flights15.4%
Scale runs 0% to 100%.
Share of scheduled departures at each local time. Times used on fewer than one flight in ten are not listed.
A 08:25 departure sits in the 8am–11am window. Across every US flight scheduled in that window the on-time rate is 83.9%, and UA 637 runs 9 points better at 92.5%. Early departures usually start with an aircraft that has not flown yet that day, which is most of why the window does well.
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Against the route
UA 637 next to IAD to AUS
Every carrier on IAD to AUS combined arrived on time 83.8% of the time across 1,018 flights, so UA 637 is 9 points ahead of it. United flew 987 flights on the same city pair under all its flight numbers, including this one, and those ran 84.5% on time. Across its whole network United Airlines managed 78.8%, which this flight beats by 14 points.
| Compared with | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| UA 637thin sample | 254 | 92.5% | 61 min | 0.79% | A+ |
| All United Airlines on IAD–AUS | 987 | 84.5% | 73 min | 0.81% | B+ |
| All carriers on IAD–AUS | 1,018 | 83.8% | 72 min | 0.79% | B+ |
| United Airlines, whole network | 830,825 | 78.8% | 73 min | 1.02% | B |
Across the year
UA 637 quarter by quarter
UA 637 did not run the same all year. Its best quarter was Apr–Jun 2026 at 96.4% on time and its weakest Jul–Sep 2026 at 82.6%, a swing of 14 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 202526 flights—
- Oct–Dec 202581 flights93.8%
- Jan–Mar 202645 flights93.2%
- Apr–Jun 202655 flights96.4%
- Jul–Sep 202647 flights82.6%
Scale runs 75% to 100%. Rows with fewer than 30 flights show a dash.
By weekday, UA 637 did best on Thursday at 97.7% on time and worst on Monday at 84.4%. Each day rests on about 36 flights, so a gap of 13 points is worth noticing but could still narrow in another year.
Arrival by arrival
How late UA 637 runs when it is late
UA 637 often beats the schedule: 137 of 252 completed flights, 54%, arrived 15 minutes or more early. The 19 late arrivals split 7 under half an hour, 5 between 30 and 60 minutes, and 7 an hour or more.
- 15+ min early137 flights54.4%
- Within 15 min96 flights38.1%
- 15–29 min late7 flights2.8%
- 30–59 min late5 flights2.0%
- 1–2 hours late6 flights2.4%
- 2+ hours late1 flights0.4%
Scale runs 0% to 100%.
Share of 252 completed flights by arrival against schedule.
Only 10 of 252 completed flights left 15 minutes late or more, too few to say how often the time is made up.
The worst days
Worst days for UA 637
The latest arrival of the period was on 13 July 2026, 6 hours 1 minute behind schedule; most of its delay minutes were filed as a late-arriving aircraft. On three of the five worst days the largest share was filed as national airspace system delay.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 13 July 2026 | 6 hours 1 minute | Late-arriving aircraft |
| 10 August 2026 | 1 hour 39 minutes | Late-arriving aircraft |
| 5 December 2025 | 1 hour 27 minutes | National Airspace System |
| 22 July 2026 | 1 hour 15 minutes | National Airspace System |
| 16 August 2026 | 1 hour 8 minutes | National Airspace System |
Delay causes
Why UA 637 runs late
Late-arriving aircraft accounts for 44% of the 1,155 delay minutes carriers reported here, and the remaining four split what is left.
- 44%Late-arriving aircraft
- 41%National Airspace System
- 11%Carrier
- 4%Extreme weather
44% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 1,155 reported delay minutes here, that single category outweighs weather by 12 to one. The split is drawn from 1,155 delay minutes reported on UA 637.
Cancellations are rare at 0.79%, below the national 1.89% 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
Badly late arrivals are rare here: only 2.8% land an hour or more behind schedule, against 8.3% nationally. Connections built on this flight are about as safe as US domestic connections get, though a cancelled flight still ignores every layover you give it.
The 1,297 miles between these two airports put this in the middle of the US network, around two and a half to three hours of block time. That is enough cruise to absorb a ten-minute late pushback and not enough to absorb thirty.
The same number turns up on seven other city pairs in the data, including AUS to LAX (89), PWM to ORD (35) and SYR to IAD (20), but none flew often enough under UA 637 to report a rate for. Carriers move flight numbers between routes, so the figures on this page apply to IAD to AUS only.
One caution: this is a thin sample. 254 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 UA 637
For a booking, UA 637 has one of the better records a US domestic flight can show: 92.5% on time and 0.79% cancelled. That is a base rate, not a promise about any single day.
Related
Where to go next
- IAD to AUS, every carrier and departure
- AUS to IAD, the return direction
- United Airlines 2337 on the same route76.7%
- Washington Dulles International (IAD) delay statistics
- Austin-Bergstrom International (AUS) delay statistics
- United Airlines on-time record
- Every United Airlines flight number with a record
- The most and least reliable flight numbers in the US
- Why the first flight of the morning is statistically safest
A flight number here means United 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, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.