The Federal Aviation Administration (FAA) last night told operators of Boeing’s 737 airplanes to carry out checks of the plane’s cabin altitude pressure switches in the latest setback for the aerospace giant.

The new directive, which comes just days after the agency found a fault in undelivered 787 Dreamliners, affects some 9,000 planes worldwide.

It covers all versions of the 737, but is not related to the issues that saw the MAX model grounded for nearly two years.

If the switches fail, it could result in the cabin altitude warning system not activating if the cabin altitude exceeds 10,000 feet (3,050 m), the FAA said.

At this point oxygen levels in the cabin could become dangerously low, it added.

The latest directive was issued after an operator reported in September that both pressure switches failed the on-wing functional test on three different 737 models.

Boeing said in a statement that it welcomed the directive, which it said “makes mandatory the inspection interval that we issued to the fleet in June.”

Operators must carry out the tests within 2,000 flight hours since the last test of the cabin altitude pressure switches, before airplanes have flown 2,000 hours, or within 90 days of the directive’s effective date.

Although Boeing initially reviewed the data and decided it did not pose a safety issue, a subsequent analysis by the FAA deemed that the failure rate was much higher than initially expected.