The Federal Aviation Administration (FAA) issued a recommendation late Sunday night (January 21) to all airlines operating Boeing 737-900ER jets to inspect the door plugs of the planes in question to ensure they were properly secured.
The agency's "Safety Alert for Operators" disclosed that some airlines have conducted additional inspections on the 37-900ER mid-exit door plugs and "have noted findings with bolts during the maintenance inspections."
Reuters reported that the advisory was made after several operators reported unspecified issues with bolts upon inspections in the aftermath of an incident where the door plug of a brand new Alaska Airlines MAX 9 jet caused a mid-air blowout.
The incident eventually forced the FAA to recommend grounding 171 Boeing 737 MAX 9 planes, which remained in effect as of Sunday until it "is satisfied they are safe to return to service."
Door Plug Issues Plague MAX 9 Fleet
While the 737-900ER was not part of the MAX fleet, it has the same optional door plug design that allowed for the addition of an extra emergency exit door when carriers opt to install more seats.
The FAA's recommendation told air carriers to perform key portions of a fuselage plug assembly maintenance procedure related to the four bolts used to secure the door plug to the airframe "as soon as possible."
In an email obtained by Reuters, a Boeing spokesperson said that they "fully support the FAA and [its] customers in this action."
The company delivered the 737-900ER to its customers from 2017 to 2019. Among US carriers, United Airlines is the only other operator of the specific 737 variant, and it said that they found loose parts on multiple grounded MAX 9 aircraft during preliminary checks, prompting them to cancel thousands of flights this month.
United added that it was extending the cancellation of its MAX 9 flights until January 26. Alaska, whose MAX 9 planes account for 20% of its fleet, previously canceled all of its flights through Sunday but has not immediately provided comment on how long it planned to extend cancellations.
The Wall Street Journal also reported that the parts that failed in Alaska's MAX 9 were made in Malaysia.
Meanwhile, Indonesian carrier Lion Air, which also operated MAX 9 planes, said that it was resuming the fleet's flights after its own checks.
United, Alaska to Also Inspect 900ERs
On the other hand, the Boeing 737-900ER has logged over 11 million hours of flight time and 3.9 million flight cycles without any issues with door plugs, the FAA added.
However, both United and Alaska said that they have already begun inspections of the door plugs on their 737-900ER fleets to see if they were also affected by the door plug issue.
United said that the inspections of their 136 737-900ER planes were "to be completed in the next few days" without disruption to their customers. As for Alaska, their inspections began several days ago, and that it has had no findings to date, but they expected to "complete the remainder of [its] -900ER fleet without disruption to our operations."
Meanwhile, Delta Air Lines also said that it "elected to take proactive measures" to inspect its own 737-900ER fleet and does not anticipate any operational impacts.
