The US Federal Aviation Administration (FAA) issued a directive to inspect cabin altitude pressure switches on all Boeing 737 aircraft.

The directive affects all 737 series aircraft, including Classic, NG, and MAX models. It urges all operators to perform tests of and replace switches if needed.

According to the FAA, the concern was caused by reports about failed switches, discovered by a certain 737 operator during tests. 

“Failure of these switches could result in the cabin altitude warning system not activating if the cabin altitude exceeds 10,000ft, at which point oxygen levels could become dangerously low,” the directive states.

The issue is unrelated to much-publicized problems with Boeing 737 MAX flight control software, according to the agency. There have been previous issues with 737 pressure switches though. The latest failures, discovered in September 2020, were investigated by Boeing and found inconsequential. FAA disagreed, which lead to the issuing of the directive.