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FAA orders checks on 9,300 Boeing 737 planes for possible switch failures:
WASHINGTON, July 15 (Reuters) - The Federal Aviation Administration (FAA) on Thursday issued a directive to operators of all Boeing Co (BA.N) 737 series airplanes to conduct inspections to address possible failures of cabin altitude pressure switches.
The directive requires operators to conduct repetitive tests of the switches and replace them if needed. The directive covers 2,502 U.S.-registered airplanes and 9,315 airplanes worldwide.
It was prompted after an operator reported in September that both pressure switches failed the on-wing functional test on three different 737 models.
The FAA said failure of the switches could result in the cabin altitude warning system not activating if the cabin altitude exceeds 10,000 feet (3,050 m), at which point oxygen levels could become dangerously low.
Airplane cabins are pressurized to the equivalent of not more than 8,000 feet (2438 m).
[...] Due to the importance of functions provided by the switch, the FAA in 2012 mandated all Boeing 737 airplanes utilize two switches to provide redundancy in case of one switch's failure.
The directive covers all versions of the 737 jetliners, including the MAX, but is unrelated to any issues related to the MAX's return to service last November.
(Score: 2) by Beryllium Sphere (r) on Monday July 19 2021, @08:06PM (2 children)
I believe that means the cabin pressure is the same as you'd have at the top of an 8,000 foot mountain. They could design it to go all the way to sea level pressure but that's a lot of force on the structure that's not required for humans to breathe.
So you go along at 37,000 feet, but bleed air from the engines puts as much pressure in the cabin as you'd get in an open plane at 8,000 feet.
(Score: 2) by sjames on Tuesday July 20 2021, @02:31AM
Unless it's a 737 with faulty switches, then, who knows?
(Score: 0) by Anonymous Coward on Tuesday July 20 2021, @04:47AM
The cabin pressure is adjustable. The pilots program in the starting altitude, the cruising altitude, and the destination altitude. The cabin pressure slowly decreases until hitting the programmed altitude pressure. As you start the decent, the pressure slowly builds back up until it matches the pressure on the ground.
Thankfully this pressure problem is only for the 10,000 warning system. There is a redundant 14,000 foot system that works slightly differently that would also warn the pilots and cabin crew if the primary system fails.