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About 505 of the 737-900ER type of planes have been delivered to airlines globally, according to Boeing data. Image Credit: Bloomberg

The US Federal Aviation Administration is recommending airlines inspect another type of Boeing Co. 737 aircraft that also has mid-exit door plugs, the same type that ultimately failed in an Alaska Airlines blowout on January 5.

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Citing an ‘added level of safety,’ the US aviation regulator said in a statement late Sunday that it was “recommending that operators of Boeing 737-900ER aircraft visually inspect mid-exit door plugs to ensure the door is properly secured.” Boeing said in a statement that it “fully supports the FAA and our customers in this action.”

The 737-900ER is an older generation aircraft type that’s not part of the Max family but has the same door plug design.

The FAA ultimately grounded 171 MAX 9 jets that contained mid-exit door plugs after a panel on the Alaska Air jet blew out mid-flight earlier this month, leaving a gaping hole that fortunately didn’t suck anyone out of the plane.

According to Boeing data, 505 of the 737-900ER type of planes have been delivered to airlines globally. The major operators of the 900ER include United Airlines Holdings Inc., Alaska Airlines and Delta Air Lines Inc. Some 900ER operators have “noted findings with bolts” during inspections, the FAA said in a separate statement. Other operators include Korean Air, Indonesia’s Lion Air, and El Al.

United, which has 136 737-900ERs in its fleet, said it started “proactive inspections” earlier this week, and expects them to be completed in the next few days. Meanwhile, its MAX 9s will continue to be grounded through Friday. Delta, which has 163 of the 900ERs in its fleet as of September last year, said in a statement it planned to undergo inspections and that it didn’t anticipate any operational impact.

Inspections of the Max 9 plug door can take up to eight hours and the visual checks required by the FAA for the 900ER are specific to four locations where a bolt, nut and pin installation is used to secure the door to the airframe. The detail of the work suggests stripping back the door plug to its bare frame to undertake the checks. Most airlines so far have stressed no impact on flights relating to the measures.

The call to widen the inspection of the door plugs comes after the FAA said it would increase its oversight of Boeing’s production and manufacturing operations. Federal regulators had already stepped up oversight of Boeing since a pair of 737 MAX crashes in 2018 and 2019 killed 346 passengers and crew. FAA inspectors are required to sign off on every 737 and 787 prior to delivery, work it had previously delegated to employees of the planemaker.

Not all models of the planes have the door plugs, depending on the seating configuration.