20240109 alaska airlines
An Alaska Airlines Boeing 737 Max-9 aircraft grounded at Los Angeles International Airport (LAX) in Los Angeles, California, US. Image Credit: Bloomberg

The US National Transportation Safety Board (NTSB) said late on Monday it could not yet tell whether a recovered cabin panel that blew off an Alaska Airlines Boeing 737 MAX 9 plane in mid-air last week had been properly attached.

The comments came after Alaska Airlines and the other US 737 MAX 9 operator, United Airlines, said on Monday they had found loose parts on multiple grounded aircraft, raising new concerns among industry experts about how Boeing’s best-selling jet family is manufactured.

The NTSB “has not yet recovered the four bolts that restrain it from its vertical movement,” NTSB engineer Clint Crookshanks told reporters at a briefing in Portland. “And we have not yet determined if they existed there.” The door plug is further fastened in place by “stop fittings” at 12 different locations along the side of the plug and the door frame. Those components hold the door plug in place and prevent it from being pushed out of the aircraft.

“The door translated up and disengaged from the stops, which then fractured the fittings,” Crookshanks said.