The Federal Aviation Administration is ordering airlines to inspect Boeing 737s after repeated failures of altitude switches.

The switch failures are related to a system to alert crew of cabin depressurization, raising concerns that "oxygen levels could become dangerously low," the FAA said, according to ABC News.

Airlines have not reported any instances of danger associated with switch failures.

An airline brought the switch problem to the FAA's attention last September after the switch failed on three different 737 models.

"A latent failure of both pressure switches could result in the loss of cabin altitude warning, which could delay flight crew recognition of a lack of cabin pressurization, and result in incapacitation of the flight crew due to hypoxia (a lack of oxygen in the body), and consequent loss of control of the airplane," the FAA said, according to ABC News.

In November, Boeing said the issue was not a threat to safety.

The FAA came back in May 2021 and said the failures "pose a safety issue" that "requires immediate action."

The switch failure is not limited to one 737 model.

Across the country the inspection order applies to around 2,500 Boeing 737 Max and NextGen models.

"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," Boeing said in a statement to ABC News.

The Boeing 737 Max was grounded in 2019 after two crashes killed 350 people.

Boeing is still recovering from the ensuing investigation. The 737 Max returned to skies last fall.

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