The FAA on Friday confirmed that it has issued an airworthiness directive (AD) requiring inspections for all Boeing 737 airliners to address possible failures of cabin altitude pressure switches. If both of the pressurization system’s dual switches were to fail during an inflight depressurization event, this could result in the cabin altitude warning system not activating if cabin altitude exceeds 10,000 feet, causing oxygen levels to be dangerously low.
The AD requires operators to conduct repetitive tests of the cabin altitude pressure switches and replace faulty switches. It applies to all 2,502 U.S.-registered 737s and 9,315 aircraft worldwide, with the tests to be performed within 2,000 flight hours of the last test of the switches, before the airplane has flown 2,000 hours or within 90 days of the AD being issued.
Acknowledging the new AD, Boeing issued the following statement: “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 AD is unrelated to any of the issues around return-to-service requirements or flight control system recertification for Boeing’s 737 Max aircraft. It is not understood to have been implemented in response to an actual dual-switch failure event.