It appears airlines and others in the aviation industry might have popped the cork a little too early on a recent Transportation Department report showing only 50 tarmac delays in October, the first time the DOT included such delays in its monthly airline report card.

For the month, the 19 carriers reporting on-time performance recorded an overall on-time arrival rate of 86% for the month, up from 78.2% for the same month last year and 84.9% from September.

The DOT identified 50 flights that sat on airport tarmacs for three hours or more, out of 554,325 flights.

Now, though, the DOT says it can’t vouch for those figures because the data used to determine the delay count is corrupted.

An analysis of the data by an outside lobby group, which prompted the DOT acknowledgment, indicates there were likely more tarmac incidents than reported.

“Internally, we were missing a key data check,” said Anne Suissa, the DOT’s director of airline information. “The checks and reviews of this data were not as thorough as they should have been. I can’t say the tarmac delay number is correct.”

Suissa said the DOT failed to give airlines clear instructions on how to report the data.

“We recognize now there was a misunderstanding,” she said.

The DOT considers any time the plane is on the ground for three or more hours with passengers and doors closed to be a reportable tarmac delay, Suissa said.

But some of the calculations that go into figuring when those delays occurred are much more complex, relying on airlines to provide total time on ground, longest time on ground and other similar data points. Major discrepancies apparently exist in those data points, calling into question the overall tarmac delay calculation, Suissa acknowledged.

Flyersrights.org, formerly the Coalition for an Airline Passengers’ Bill of Rights, alerted the DOT to the discrepancies.

“It looks like the airlines are just filling in numbers,” said Mark Mogel, Flyersrights’ research director.

In reporting the analysis to the DOT, Mogel highlighted one flight where an aircraft was stuck at an airport for three hours and 48 minutes but was reported to be “on the ground” for only four minutes.

“It appears to me that a great deal of the data, possibly a majority, is incorrect,” Mogel said.

Suissa said the airlines apparently were confused about what information the DOT wanted. The numbers, she agreed, simply don’t add up.

To make matters worse, she said, the data were not properly vetted by the agency.

“There has been a culture of just getting the data out instead of getting it right,” Suissa said. “Now, we have a renewed focus on data quality.”

She said the DOT was working on a fix it can send to the airlines to better explain the information it needs reported.

In the meantime, the DOT says, the Bureau of Transportation Statistics, the government agency that collected and disseminated the data, is posting a disclaimer on its website that some of the tarmac delay data may have been misreported by some airlines.