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Flight Reliability

UA 5539 · United Airlines

ACV → San Francisco (ACV–SFO)90% of its flights flew this route. The rest (PIA–DEN, SAV–ORD) are included in these numbers.

77
Usually Fine
WanderNerd Reliability Score
80%
Arrive within 15 minutes
6 min
Average arrival delay
2.4%
Cancelled
10 min early
Median arrival delay

Based on 337 historical flights. Data through May 2026.

What the data says

Morning-you made the right choice.

UA 5539 departing between 6–9 AM arrived on time 91% of the time, versus 79% between 3–6 PM.

Sunday scaries are real for this one.

UA 5539 arrived on time 88% of the time on Fridays and just 70% on Sundays. That gap is worth planning around.

Better than the ACV–SFO route average.

UA 5539 arrived on time 80% of the time, versus 68% across the ACV–SFO route.

Recent months have been rougher.

UA 5539 arrived on time 67% of the time over the last three months in the data, compared with 80% in the three months before that.

The breakdown

On-time by weekday
  • Mon77%(51 flights)
  • Tue86%(44 flights)
  • Wed77%(48 flights)
  • Thu76%(49 flights)
  • Fri88%(51 flights)
  • Sat85%(39 flights)
  • Sun70%(46 flights)
On-time by departure window
  • 6–9 AM91%(23 flights)
  • 3–6 PM79%(299 flights)
  • 6–9 PM—(6 flights)
On-time trend by month
54%
May

Jun 93% → May 54% on time

On-time arrival percentage by month
MonthOn-time percentageFlights
June 202593%30
July 202577%31
August 202587%31
September 202593%30
October 202574%31
November 202578%27
December 202586%28
January 202683%29
February 202671%24
March 202696%22
April 202653%19
May 202654%26
Departures on time
82%
Diverted
0.3%
Flights flown
328
Months covered
12

Same route, other flights

Keep nerding

Based on 337 historical flights, because apparently we checked. Historical flight data: U.S. Bureau of Transportation Statistics, June 2025 – May 2026. Data through May 2026. How we calculate this.