FAA to require more frequent testing of low cabin pressure warning systems on Boeing 737s

The Federal Aviation Administration (FAA) will require more frequent testing of low cabin pressure warning systems on Boeing 737s.

The FAA issued an Airworthiness Directive on Thursday, which was prompted by “reports of latent failures of the cabin altitude pressure switches.”

The directive requires “repetitive functional tests of pressure switches,” and to replace the switches if necessary.

Operators of the plane have to test the parts every 2,000 flight hours. According to The Associated Press, testing currently happens on a 6,000-hour interval.

Boeing 737s have two cabin altitude pressure switches that detect if a certain cabin pressure altitude has been exceeded and to signal parts of the system that warn the flight crew.

When these systems fail, they fail latently — meaning there’s no signal to flight crew or maintenance personnel.

The latent failure of both switches would delay flight crew recognition of a lack of cabin pressurization, and result in hypoxia, a lack of oxygen in the body. 

The FAA said in its directive that it received reports of the latent failures. In September 2020, an operator reported that both switches failed on three of the airplanes during a test. 

Boeing originally said the failure was not a safety issue, but the FAA said it determined in May 2021 that the failure rate of both switches is “much higher than initially estimated.”

The FAA told The Hill in a statement that the order effects 2,502 U.S.-registered airplanes and 9,315 airplanes worldwide.

Boeing added that it welcomes the change.

“Safety is our highest priority, and we fully support the FAA’s direction, which makes mandatory the inspection interval that we issued to the fleet in June,” the company said.