In the aftermath, under intense pressure from consumer advocates, the government adopted a regulation that punished airlines for keeping passengers on a plane for more than three hours.

But they may have gone too far, new research suggests. The new regulations have “significantly increased” the number of passenger delays, according to a new study by Dartmouth College and the Massachusetts Institute of Technology.

How much of a delay? Each minute of time saved waiting on the tarmac translates into roughly three minutes of total passenger delay, according to the research.

“This is due primarily to increases in flight cancellations, resulting in passengers requiring rebooking, and often leading to extensive delays in reaching their final destinations,” says Vikrant Vaze, an assistant professor at Dartmouth’s Thayer School of Engineering.

Government data indicates about 1 in 5 flights is delayed. (A flight is considered delayed when it arrived 15 or more minutes than the schedule.) From October 2014 to 2015, the latest period for which statistics are available, 80 percent of flights operated on-time, according to the Bureau of Transportation Statistics. A year before, flights were running 77 percent on-time. A year before that, the national on-time average was 79 percent. The research, based on a hypothetical model, suggests there should have been fewer delays.

The study recommends the U.S. Department of Transportation (DOT) take the following steps to correct the over-regulation:

• Changing its existing tarmac delay rules to a more flexible version. It proposes increasing the tarmac time limit to 3.5 hours from the current 3 hours.
• Applying the tarmac delay rules only to flights with planned departure times before 5 p.m.
• The researchers also recommends the tarmac time limit be defined in terms of when the aircraft must begin returning to the gate, instead of when passengers are allowed to deplane.

Now what?

The study has drawn a strong reaction from critics and prompted the question: What’s next? Will the research pressure the government to loosen its tarmac delay rules?

The airline industry hopes so. “The tarmac delay rule has actually caused more harm than good for the traveling public,” says Jean Medina, a spokeswoman for A4A, a trade group for some of the major domestic airlines. “The rigid structure of the rule in its current form has resulted in unnecessary delays in getting passengers to their intended destination, as carriers seek to avoid overly punitive fines from Department of Transportation.”

Medina says reforms are needed, including adjusting the rule to provide pilots more flexibility to complete flights. The airline industry, she adds, “remains committed to working with the Department of Transportation to ensure the rule benefits both customers and airline employees alike.”

A DOT representative said the agency hadn’t reviewed the new research yet. But the agency pointed out that a January 2014 study on the impact of the tarmac delay rule on flight cancellations concluded that the rule has virtually eliminated tarmac delays of more than three hours and that there was relatively little impact on flight cancellations.

Advocates oppose changes

The consumer advocates who pushed for the existing tarmac regulations insisted that the research is flawed and that no regulatory changes are necessary. Kendall Creighton, a spokeswoman for FlyersRights.org, says passengers support the existing three-hour rule.

“This action was the consequence of thousands of extended tarmac delays of nine hours or more, with horrifying conditions on-board commercial jets in the US,” she says. “Passengers witnessed children passing out due to heat exposure, overflowing toilets, cramped spaces, no food or water, screaming babies and no hope of ever getting off the plane as no laws were in place to protect them.”

Creighton claims the new study is timed to try to persuade both Congress and the DOT to either extend the tarmac delay rule or reduce the fines imposed for tarmac delays, but that it does nothing to help airline passengers. “Instead, it would allow the airlines more flexibility to overschedule, and prevent passenger migration in the event of a long ground delay,” she says.

Vaze, the Dartmouth researcher, says the paper is a scientific study that simply tried to accurately estimate the positive and negative effects of the tarmac delay rule on the passengers. And he’s just getting started. Next, his team plans to examine the rule’s impact on commercial airlines across different years, as well as on commercial airline schedule decision-making.