Boeing 737 MAX 9 Fleet Grounded Following In-Flight Loss of Cabin Door Plug

A diagram of a Boeing 737-9 mid-cabin door plug and components released by NTSB. (Image: Boeing)

The Federal Aviation Administration has grounded 171 in-service Boeing 737 MAX 9s following an Alaska Airlines flight involving the aircraft type last week. According to the emergency airworthiness directive (AD) issued by the FAA on Jan. 8, the 737-9 operated as flight 1282 by Alaska involved the in-flight loss of a "mid cabin door plug, which resulted in a rapid decompression of the airplane."

"The FAA is issuing this AD to address the potential in-flight loss of a mid cabin door plug, which could result in injury to passengers and crew, the door impacting the airplane, and/or loss of control of the airplane," the FAA notes in the AD. The AD is only applicable to 737-9s that have the same mid cabin door plug installed that was featured on the flight 1282 aircraft.

The Alaska Airlines flight incident is being investigated by the National Transportation Safety Board (NTSB), Boeing and the FAA to discover what ultimately prompted the loss of the mid cabin door plug. Flight 1282 departed Portland International Airport on Friday Jan. 5, and was approaching its cruising altitude traveling at 400 mph when a 4-foot piece of the fuselage "covering an unoperational emergency exit behind the left wing detached from the aircraft," according to Associated Press coverage of the accident.

NTSB Chair Jennifer Homendy held a media briefing on Monday providing some of the latest updates for the ongoing investigation into the incident. The agency was able to retrieve the door plug after it was discovered still in-tact in the backyard of a Portland high school teacher.

"We cannot tell you at this time how, or why, we do not have that information," Homendy said. "We will have that information. It's going to take time and we're going to have to analyze the components and the door plug in our lab to be able to figure out how this happened."

Alaska Airlines has also released several updates about the ongoing investigation on its website. The airline reported the cancellation of 140 total flights through Monday, Jan. 8.

“As our maintenance technicians began preparing our 737-9 MAX fleet for inspections, they accessed the area in question. Initial reports from our technicians indicate some loose hardware was visible on some aircraft,” Alaska Airlines writes in a Jan. 8 statement.