The US Federal Aviation Administration(FAA) will not impose any new standards on the airlines regarding seat size, as the issue does not pose an immediate safety risk to passengers.

In a letter, the agency said it could not find evidence that existing seat width and legroom will slow down passenger evacuations.

The letter was written in response to last year’s order by the US Court of Appeals for the District of Columbia Circuit asking the FAA to re-evaluate its seating safety rules after a nonprofit citizens group called Flyers Rights filed a lawsuit against the FAA.

According to the lawsuit, tighter seating and bigger passengers could hinder evacuations.

“The FAA has no evidence that a typical passenger, even a larger one, will take more than a couple of seconds to get out of his or her seat.”

In a filing, the FAA said it could not find evidence that current seat width and legroom  or the increasing size of passengers will slow down evacuations. The agency also said it takes more time for flight crews to open the exit door than it does for passengers to get up from their seats.

In the letter sent to Flyers Rights, the FAA said: “The FAA has no evidence that a typical passenger, even a larger one, will take more than a couple of seconds to get out of his or her seat.”

Flyers Rights alleged that the average seat width shrunk from nearly 18 inches to 17 inches, while the distance between seats, called pitch, has gone from an average of 35 inches to 31 inches, as low as 28 inches for some airlines.

Flyers Rights president Paul Hudson said: “This response is mainly couched in the idea that they don’t know of evidence that larger passengers in smaller seats, and older passengers, would be able to get out as quickly as smaller passengers, younger passengers.”

The organisation is expected to appeal the FAA’s assessment.