WASHINGTON — Americans have gotten bigger. Airplane seats have gotten smaller. That pairing has led to a debate over whether the Federal Aviation Administration should redefine its definition of seat safety.

The agency has long maintained that if airplane seats — no matter their size — don’t extend the time needed to evacuate beyond 90 seconds, it sees no reason to set minimum standards. As for the comfort of those seats? That’s between the airlines and their customers.

But consumer groups, health experts and some members of Congress disagree, saying it’s a mistake for the FAA to only consider the effect smaller seats might have on evacuations. They say it doesn’t take into account other potential health risks passengers could face when forced to sit in small spaces for extended periods of time.

Prodded by lawmakers and consumer advocates, the FAA recently opened the door to what some hope could lead to new regulations setting minimum seat sizes. Any such attempt would likely face strong opposition from the airline industry.

“[Safety is] also when we’re in that airplane in normal operations,” Mica Endsley, government relations chair for the Human Factors and Ergonomics Society and a former chief scientist for the U.S. Air Force. “How safe is it for people to occupy those seats? Things that have impacts on the human body go beyond just evacuation.”

The numbers tell the story about how today’s air passengers and planes have changed over the years.

According to the Centers for Disease Control and Prevention, the average American man is about 30 pounds heavier, at 198 pounds, than in the 1960s. The average American woman weighs 170, also about 30 pounds more. About 40 percent of the population is considered obese, a number that is projected to reach half by 2030.

At the same time, the width of seats on many U.S. airlines has shrunk from about 18.5 inches to 17 inches. And seat pitch — the distance from one point in a seat to the same point in a seat in front or behind it — has decreased from an average of 35 inches to 31 inches. On some airlines, that distance is 28 inches.

An airline industry trade group says despite the downsizing, today’s airplane seats “continue to meet or exceed federal safety standards.”

“Airlines continue to invest in a wide range of innovative technologies to maximize personal space in the cabin while maintaining a level of comfort passengers expect,” Airlines for America said in a statement. “Safety is, and always will be, our top priority and we support the federal government’s determination regarding what seat size is safe.”

The FAA in August began asking the public to weigh in on whether it should regulate the size of seats on commercial aircraft as “necessary for passenger safety.” Nearly 12,000 individuals and organizations have left opinions, with comments allowed through the end of October.

Many expressed hope the agency would intervene and set a standard for seat sizes.

“Most Americans currently struggle to get in and out of seats on planes when boarding and disembarking in normal circumstances let alone in emergency situations,” one woman wrote. “There should be a minimum standard of seat dimensions.”

“As a lifelong frequent traveler, this initiative from the FAA is essential for safety,” responded another. “Not only for emergency evacuation, but to quell the air rage that has festered during and after the pandemic. Angrier people make everyone less safe!”

“Please consider the voices of most Americans,” pleaded another. “Traveling should be something we can do safely and comfortably. Make more space for people who have larger bodies, differently abled bodies.”

Only a handful of those who responded said seats already were an adequate size.

As part of a 2018 bill to fund the FAA, Congress directed the agency to take steps it hoped might lead to clarity on airplane seat sizes, including testing whether small seats would pose a safety hazard in an emergency. It was the highest-profile effort so far to limit the dwindling size of airplane seats. Lawmakers directed the agency to issue regulations for seat sizes and gave it an October 2019 deadline.

FAA officials declined to comment on the issue.

At the end of 2019, the FAA staged drills using volunteers to test whether smaller seats and less personal space affected their ability to evacuate. It was the first time the agency had specifically examined whether the size or space between seats could affect passengers’ ability to quickly leave an aircraft.

The report, released earlier this year, found smaller spaces did not impede participants’ ability to meet the 90-second evacuation standard. The study’s findings drew sharp criticism from Rep. Steven Cohen, D-Tenn., who has spent years urging the FAA to set minimums for the size of airplane seats.

“I am disappointed but not surprised that the flawed study came to the foregone conclusion the airline industry dictated,” Cohen earlier this year. “The flying public cannot rely on the results of this study nor should seat sizes be based solely on the study’s results.”

Endsley, the former Air Force scientist, said she worries that unless the FAA establishes minimum standards, seats and personal space will continue to shrink.

“They’ll just keep cramming more and more people in there,” she said. “If you establish a common regulation, nobody is incentivized to go below that standard.”

Others argue requiring seats to be a certain size might involve trade-offs that the public may not embrace, such as a possible rise in airfare if fewer passengers are in a plane.

“There are lots of ways that the lack of space can be a health concern and whether the FAA wants to take that on or not, I’m not sure. But in the end we’ll end up having to pay for it and people have been resistant to doing that,” said Matthew Parkinson, a professor of engineering design, mechanical engineering and industrial engineering at Pennsylvania State University.

Paul Hudson, president of FlyersRights, a nonprofit that advocates for airline passengers, has called on the FAA to establish seat-size minimums for years.

In 2016, his group asked the U.S. Court of Appeals for the D.C. Circuit to impose a moratorium that would stop airlines from reducing the size of seats, but the request was denied. Judge Patricia Millett, however, instructed the FAA to explain why smaller seats were not an increased safety hazard. In mid-September, the group was back before the same court, asking a three-judge panel to compel the FAA to issue a rule on seat-size dimensions.

At the hearing, Martin Totaro, appearing on behalf of the FAA, said the agency disagreed with the nonprofit’s interpretation that Congress intended the FAA to issue regulations on seat size. Rather, he argued, lawmakers were directing the agency to “get information from the public to take a fresh look at the connection between seat dimensions and passenger safety.”

Whether the courts will force the FAA to establish standards for seat size or whether the FAA will do so based on its own review isn’t clear. Still, many say it’s time for the agency to act.

James Stewart, 71, of California, said safety and comfort are inextricably linked.

“When you give them comfort, you will get safety,” he wrote in his submission to the FAA. “A passenger who has been sitting in a cramped position for several hours is not going to be able to react as fast as someone who is relaxed and comfortable.”

Stewart said in an interview that at 6-foot-3, he recognizes he might be an outlier when it comes to height, but even average-size people are squeezed into airplane cabins these days. As for the effect such a mandate could have on ticket prices? Stewart scoffed.

“They’re going to go up no matter what we do,” he said.