WASHINGTON, July 15 (Reuters) – The Federal Aviation Administration (FAA) on Thursday issued a directive to operators of all Boeing Co (BN) 737 series aircraft to perform inspections to remedy possible aircraft failures. cabin altitude pressure switches.
The directive obliges operators to carry out repetitive tests of switches and to replace them if necessary. The directive covers 2,502 airplanes registered in the United States and 9,315 airplanes worldwide.
It was triggered after an operator reported in September that both pressure switches had failed the under-wing functional test on three different 737 models.
The FAA said the failure of the switches could prevent the cabin altitude warning system from activating if the cabin altitude exceeds 10,000 feet (3,050 m), in which case oxygen levels could become dangerously low.
Aircraft cabins are pressurized to the equivalent of no more than 8,000 feet (2,438 m).
Boeing said it supports “the FAA directive, which mandates the inspection interval we assigned to the fleet in June.” The FAA directive did not report any in-flight switch failures.
The FAA said on Thursday that the tests must be completed within 2,000 flight hours of the cabin altitude pressure switches last tested, before the planes have completed 2,000 flight hours, or within 90 days. following the date of entry into force of the directive.
Boeing first looked at the problem, including the expected failure rate of the switches, and found it not to be a safety concern.
Subsequent investigation and analysis led the FAA and Boeing to determine in May that “the failure rate of the two switches is much higher than initially estimated and therefore poses a safety concern.” Boeing declined to say what the failure rate was.
The FAA added that it “does not yet have sufficient information to determine what caused this surprisingly high failure rate.”
Due to the importance of the functions provided by the switch, the FAA in 2012 required that all Boeing 737 aircraft use two switches to provide redundancy in the event of a switch failure.
The directive covers all versions of 737 airliners, including the MAX, but is not related to any issues with the MAX returning to service last November.
Reporting by David Shepardson; Editing by Leslie Adler and Peter Cooney
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