WASHINGTON - The Federal Aviation Administration said on Monday it is requiring inspections of 2,600 Boeing 737 airplanes because passenger oxygen masks could fail during an emergency due to a retention strap.

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The FAA said it was requiring the inspections of 737 MAX and Next Generation airplanes after multiple reports of passenger service unit oxygen generators shifting out of position, an issue that could result in an inability to provide supplemental oxygen to passengers during a depressurization event.

The FAA said its airworthiness directive was immediately effective and requires inspections and corrective actions if needed within 120 to 150 days based on the 737 model.

Boeing, which on June 17 issued a bulletin to airlines calling for visual inspections, said Monday it had told airlines to update a subset of the restraining straps on 737 oxygen generators after a new adhesive introduced on the straps in August 2019 had been seen under certain circumstances to allowed units to shift up to three quarters of an inch.

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"We have gone back to the original adhesive for all new deliveries to ensure the generators remain firmly in place, as intended," Boeing said, adding inspections of the in-service fleet and undelivered airplanes have not identified any units that failed to operate properly.

The FAA said its airworthiness directive was immediately effective and requires inspections and corrective actions if needed within 120 to 150 days based on the 737 model. The FAA is also barring airlines from installing potentially defective parts.

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Airlines must conduct a general visual inspection and if needed replace oxygen generators with new or serviceable oxygen generators, strap thermal pads and reposition impacted oxygen generators, the agency said.