Airline passengers who have long felt squished in cramped seats suffered a setback on Friday as a U.S. appeals court refused to order the Federal Aviation Administration (FAA) to adopt minimum requirements for seat size and spacing.

The D.C. Circuit Court of Appeals said an advocacy group, FlyersRights.org, had no right to force the FAA to adopt seating rules because it was not "clear and indisputable" that tight seating, while uncomfortable, was also dangerous.

Congress had in 2018 given the FAA one year to establish minimum seating dimensions including pitch, the distance between seatbacks, that were "necessary" for passenger safety.

No such rules yet exist, though airlines must be able to evacuate passengers within 90 seconds in emergencies. Airline margins could suffer if carriers were forced to reconfigure planes.

Writing for a three-judge panel, Circuit Judge Justin Walker rejected FlyersRights' claims that tight seating materially slowed emergency exits and posed medical risks such as blood clots, saying the FAA had no compelling evidence of either.

"To be sure, many airline seats are uncomfortably small. That is why some passengers pay for wider seats and extra legroom," Walker wrote. "But it is not 'clear and indisputable' that airline seats have become dangerously small.

"Unless they are dangerously small, seat-size regulations are not 'necessary for the safety of passengers,'" he added.

Paul Hudson, president of FlyersRights, said the decision ignored Congress' intent that minimum standards be considered, and passengers could expect seating to shrink to "torture class" if the FAA did nothing.

FlyersRights is directly petitioning the FAA for new rules.

"Even rules codifying the status quo would stop seat dimensions from getting even smaller," its lawyer Michael Kirkpatrick said in an interview.

The FAA declined to comment. Airline trade groups have opposed new seating rules.

In November, six Democratic U.S. senators led by Majority Leader Chuck Schumer urged the FAA to ban airlines from further shrinking seat sizes and leg room.

FlyersRights has said typical average seat pitch has shrunk four to seven inches, to as little as 28 inches (71 cm), and seat width has also shrunk since airline deregulation in 1978, while passengers have gotten larger.

The case is In re Flyers Rights Education Fund Inc, D.C. Circuit Court of Appeals, No. 22-1004.

(Reporting by Jonathan Stempel in New York and David Shepardson in Washington; Editing by Bill Berkrot and Richard Chang)