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Flight Reliability

DL 4027 · Delta Air Lines

Seattle → Ontario (SEA–ONT)87% of its flights flew this route. The rest (FSD–MSP, CLE–DTW) are included in these numbers.

96
Nerd Approved
WanderNerd Reliability Score
89%
Arrive within 15 minutes
3 min early
Average arrival delay
0.3%
Cancelled
10 min early
Median arrival delay

Based on 356 historical flights. Data through May 2026.

What the data says

Friday is doing you no favors.

DL 4027 arrived on time 96% of the time on Saturdays and just 76% on Fridays. That gap is worth planning around.

A bit ahead of the SEA–ONT route.

DL 4027 arrived on time 89% of the time, versus 83% across the SEA–ONT route.

Better than the Delta Air Lines network average.

DL 4027 arrived on time 89% of the time, versus 81% across the Delta Air Lines network.

It basically never cancels.

Out of 356 scheduled flights, only 0.3% were cancelled.

The breakdown

On-time by weekday
  • Mon90%(52 flights)
  • Tue94%(52 flights)
  • Wed88%(50 flights)
  • Thu92%(49 flights)
  • Fri76%(50 flights)
  • Sat96%(49 flights)
  • Sun89%(53 flights)
On-time by departure window
  • 3–6 AM90%(20 flights)
  • 6–9 AM—(5 flights)
  • 6–9 PM89%(330 flights)
On-time trend by month
90%
May

Jun 87% → May 90% on time

On-time arrival percentage by month
MonthOn-time percentageFlights
June 202587%30
July 202584%31
August 2025100%31
September 202583%30
October 202584%31
November 202596%28
December 202589%28
January 202693%30
February 202689%28
March 202683%30
April 202693%28
May 202690%30
Departures on time
89%
Diverted
0%
Flights flown
355
Months covered
12

Same route, other flights

Keep nerding

Based on 356 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.