The on-time ranking did not notice WestJet's strike.
TL;DR [show]
Cirium's August 2026 on-time report ranks WestJet first in North America at 82.55% on-time, its fourth consecutive month at the top. In the same month WestJet's flight attendants struck network-wide, and the airline cancelled 1,230 of 19,652 flights, about one in sixteen, finishing with the worst completion factor in the ranked group at 93.74%. Both facts survive together because a cancellation is not a late arrival: it leaves the numerator and the denominator at the same time. The inversion runs the other way too. Southwest posts the worst-sounding number in the release, on-time 68.28%, late nearly a third of the time, and the best completion factor in North America at 99.22% against Delta's 98.23, United's 98.53, Alaska's 98.57 and American's 97.72. The piece argues the metric is not incomplete but inverted for the question a passenger actually asks, which is whether they arrive today rather than whether they arrive within fifteen minutes, and that the gap is worst at Southwest precisely because it holds no interline agreements, so its cancelled passenger waits for the next Southwest seat. No gaming is alleged and none is needed: a ranking that does not count cancellations ranks the airline that cancelled, without requiring anyone's intent.
Cirium published its August 2026 on-time performance report, and WestJet is first in North America at 82.55%. Fourth consecutive month at the top.
Also in August: WestJet's flight attendants walked out. The stoppage was network-wide, the recovery after the August 3 tentative agreement was messy, and the airline cancelled 1,230 of 19,652 flights, one in sixteen. Its completion factor for the month, 93.74%, is the worst in the group Cirium ranked.
So how do those two facts live in the same month?
Because a cancelled flight is not a late flight. It leaves the numerator and the denominator at the same moment. On-time performance counts arrivals within fifteen minutes of schedule among the flights that arrived, and a flight that never operated is not late, not early, not anything. It is absent. A strike that removes one flight in sixteen from the schedule does not make the rank worse. It removes the evidence.
The inversion runs the other way too.
Southwest posted the worst-sounding number in the release. On-time 68.28%, which is to say late nearly a third of the time. It also posted the best completion factor in North America, 99.22%, against Delta at 98.23%, United at 98.53%, Alaska at 98.57% and American at 97.72%. Roughly 922 cancellations across the month. The airline that looks worst on the headline metric is the one most likely to actually fly you.
Which is the number a passenger wants? Not the fifteen-minute one. Nobody stands at a gate hoping for punctuality in the aggregate. They want to sleep in the city they bought a ticket to. A twenty-five minute delay and a cancellation sit on different scales. Only one of them ends with a hotel voucher and a morning off work.
That gap is widest at Southwest, for a structural reason rather than a service one. Southwest holds no interline agreements. When Delta cancels, Delta can put you on American. When Southwest cancels, you wait for the next Southwest seat, which on a full late-summer weekend is a genuinely different kind of wait. The carrier with the best completion factor in North America is also the carrier for whom a cancellation costs the passenger the most, so it has the strongest operational reason to keep the flight, and the metric gives it nothing for doing so. With Southwest, behaviour runs downstream of structure, and it usually does.
Gary Leff, who wrote up the report, puts it carefully: an airline that is quick to cancel may look better than one that sticks it out. Nobody is alleging that WestJet cancelled to protect a rank, and the August numbers have a labour dispute sitting under them.
No intent was required, which is what gaming-stories get wrong about metrics. A ranking that does not count cancellations will inevitably rank the airline that cancelled, and it will do so without anybody deciding to game it. The incentive does not need to be taken up to be real. It sits there, paying for a behaviour nobody has to choose.
Fourth consecutive month, incidentally. The strike sits in the middle of the streak.
One month of data is one month of data, and the ranking is monthly, so September will say something different. But the structure does not reset with the calendar. Cirium is not ranking reliability. It is ranking the flights that operated, which is a claim about the schedule that survived rather than the one that was sold.
—TJ