The U.S. Federal Aviation Administration issued a recommendation advising airlines operating Boeing 737-900ER aircraft to conduct inspections of door plugs to ensure their proper securement.

This guidance comes after some operators reported unspecified issues with bolts during inspections.

The FAA’s recommendation follows its grounding of 171 Boeing 737 MAX 9 planes following a mid-air cabin incident on January 5, where a door plug on an eight-week-old Alaska Airlines MAX 9 jet experienced a blowout.

While the 737-900ER is not part of the newer MAX fleet, it shares the same optional door plug design, allowing for the addition of an extra emergency exit door when carriers choose to install more seats.

The FAA is urgently checking 737 MAX aircraft

The FAA disclosed in a “Safety Alert for Operators” that some airlines had conducted additional inspections on the 737-900ER mid-exit door plugs and discovered issues with bolts during maintenance inspections.

Fuselage plug

The FAA recommended that air carriers promptly perform crucial portions of a fuselage plug assembly maintenance procedure related to the four bolts used to secure the door plug to the airframe.

A Boeing spokesperson expressed full support for the FAA’s action. Boeing first delivered the 737-900ER in 2007, with the last one delivered in 2019.

Both Alaska Airlines and United Airlines (UAL.O), the only two U.S. carriers operating the MAX 9, reported finding loose parts on multiple grounded MAX 9 aircraft during preliminary checks earlier this month. As a result, they have had to cancel thousands of flights this month due to the grounding.

Remain grounded

The FAA stated on Sunday that MAX 9 planes would remain grounded until it is satisfied that they are safe to return to service.

United Airlines extended the cancellation of its MAX 9 flights through January 26, while Alaska Airlines, which has 20% of its fleet consisting of MAX 9 planes, had previously canceled all flights through Sunday.

The airline did not immediately comment on the duration of the extension of its cancellations.

Number of flights

In contrast to the MAX 9, which experienced the door-plug issue on a new plane with a low number of flights, Boeing 737-900ER aircraft have accumulated over 11 million hours of operation and 3.9 million flight cycles.

The FAA noted that the door plug “has not been an issue with this model.”

Both United and Alaska have initiated inspections of the door plugs on their 737-900ER fleets. United, which operates 136 of these aircraft, expects inspections to be completed in the next few days without causing disruptions to its customers.

Alaska Airlines began its inspections several days ago, reporting no findings to date and expecting to complete the remainder of its -900ER fleet without disruptions to its operations.