Flights with Two Hour Ground Delays Were Twice as Likely to Cancel This Summer

I know that I said I wouldn’t bother writing about ground delays again until some new, interesting data came out, and now, we have some. The funny thing is that I didn’t even see it. It was only brought to my attention by the DOT as part of the agency’s campaign to convince the world that the ground delay rule is having no ill effects, but clearly we read the data differently. While the DOT sent this data to me as proof in its favor, what I saw was a doubling of the rate of cancellations when flights were held on the ground for more than two hours.

Here’s the chart with the data that DOT spokesperson Jill Zuckman sent me:

Ground Delays Over Two Hours

It really shows how data interpretation can vary widely. According to Jill, “the data shows that there were fewer cancellations involving flights that experienced tarmac delays of more than 2 hours during May-August 2010 when compared to the same period in 2009.” Well yeah, that’s true, but more importantly, it shows that when airplanes were delayed for two hours on the ground, they were twice as likely to cancel this year than last. Now that to me seems like proof that the ground delay rule is causing cancellations, no? I mean, without the rule, you would assume that the historical percentage would still be the rate we’d see today.

But let’s go back to the aggregate number. Jill and the DOT look at this and say that the “decline can be attributed to the fact that the average number of 2+ hour tarmac delays was much lower in the first 4 months of the post rule period than in the same 4 month period in 2009.” Yes, that’s true. But why is that the case? Airlines have probably started canceling flights further in advance. Or maybe the weather just wasn’t as bad this summer as it was last. (I already dug in and showed that earlier this summer.) There are a lot of reasons why cancellations numbers can fluctuate, but in general it’s been hard to pin down the reasons on a single event until this nugget of data was brought to my attention.

Let’s think about this. It’s no surprise that the number of 2 hour ground delays is down year over year, right? I mean, when you have harsh penalties kicking in at 3 hours, of course you’re going to make changes to prevent anything staying out there over 3 hours. We knew that, but my hypothesis has been that it will negatively impact cancellations. That seems to be the case here. It looks like once airplanes are sitting on the ground for over two hours, it means there’s probably a weather problem or some other operational event that’s preventing airplanes from getting to the gate. Last year, of those flights, 4 to 8 percent were canceled in any given month. But this year, it’s 10 to 14 percent. Why would that be? Because the 3 hour rule is forcing airplanes to come back and cancel.

Without having the airlines give us specific numbers, this is the closest I’ve seen to something showing that there without a doubt have been more cancels this year because of the rule.

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