Air-safety officials probing last week’s fuselage blowout on a Boeing Co. 737 aircraft have turned their attention to four bolts they’ve been unable to locate and said they may widen their investigation beyond the Max 9 variant after multiple airlines found loose parts.

The bolts were meant to secure the door panel that suddenly broke loose on Jan. 5, when Alaska Airlines Flight 1282 was climbing toward cruising altitude with 171 passengers aboard. Tightened properly, they prevent the panel from sliding upward past the 12 stopper tabs that bind it to the aircraft’s fuselage. 

“We have not yet recovered the four bolts that restrain it from its vertical movement,” Clint Crookshanks, an NTSB engineer, said at a press conference Monday night. “We have not yet determined if they existed there. That will be determined when we take the plug to our lab in Washington, DC.”

Alaska Air Group Inc. and United Airlines Holdings Inc. have discovered loose bolts after the Federal Aviation Administration grounded the Max 9 and ordered carriers to inspect the planes. A missing washer was found on one plane in India, regulators there said Tuesday. 

National Transportation Safety Board Chair Jennifer Homendy said Monday that her agency would consider broadening the probe into other 737 Max models. Such a move would bring deeper scrutiny for Boeing and its manufacturing processes, magnifying the setback as the US planemaker seeks to get the aircraft back into service and avoid a lengthy grounding. 

“We need to first and foremost figure out what happened here on this aircraft,” Homendy said at the press briefing. “If we have a bigger system-wide, or fleet issue, we will issue an urgent safety recommendation to push for change.”

Up and Out

NTSB investigators said they have determined that the door panel on Flight 1282 moved upward before ejecting and causing a rapid decompression of the aircraft. Roller guide tracks that normally allow for the hinged panel, or plug, to swing outward when the bolts are loosened were fractured. 

The plugs cover an opening on the Max 9 that can be used for emergency doors. Some airlines, including United and Alaska, cover them up because they aren’t needed for their seat configurations.

United said Monday there have been signs of “installation issues” in some of its aircraft. Regulators in India said Boeing recommended a one-time inspection of all 737 Max jets for possible loose hardware after a local airline found a missing nut and washer in the rudder area of one 737 Max, the Directorate General of Civil Aviation said Tuesday. No Indian carrier operates the Max 9 subtype.

Shares of Boeing and key fuselage supplier Spirit AeroSystems Holdings Inc. have plummeted in the wake of the Alaska Air accident and groundings. Boeing fell 8% on Monday, its biggest drop since October 2022. Spirit slid 11%.

Ryanair Holdings Plc CEO Michael O’Leary, one of Boeing’s biggest customers for the 737 Max, told the Financial Times in an interview that the planemaker needs to “improve quality control.” In December, Boeing asked operators of newer Max jets to inspect the rudder area for loose hardware after an international operator discovered a missing nut and the planemaker found a loose one on an undelivered aircraft. 

Boeing Chief Executive Officer Dave Calhoun, who aims to increase production on the cash-cow Max this year, canceled an executive gathering this week and will instead hold an all-hands meeting on Tuesday focused on safety. 

While the NTSB was able to explain in great detail which parts came loose onboard Alaska Air Flight 1282, it’s yet to determine exactly why the accident happened. 

NTSB teams studying the aircraft meanwhile found “no discrepancies” between the door plug that blew off Alaska Airlines Flight 1282 and the intact identical one on the other side of the plane. The door panel has since been recovered on the ground, while other pieces of evidence, such as the cockpit voice recorder, proved unusable. 

As air safety investigators continue to collect evidence, Boeing took the first step toward returning its grounded 737 Max 9 jetliners to service, issuing guidance to airlines on what inspections are needed to prevent another midair fuselage blowout.

“As operators conduct the required inspections, we are staying in close contact with them and will help address any and all findings,” Boeing said in a statement. “We are committed to ensuring every Boeing airplane meets design specifications and the highest safety and quality standards.”

Before the Federal Aviation Administration will allow the planes to return to the air, carriers must “complete enhanced inspections which include both left and right cabin door exit plugs, door components, and fasteners,” the FAA said in its statement. “Operators must also complete corrective action requirements based on findings from the inspections prior to bringing any aircraft back into service.”

Alaska Air Flight 1282 was carrying 177 passengers and crew when the blowout of the panel occurred. The fact there were no people sitting in seats 26A and 26B and there weren’t more serious consequences was just by chance, Homendy has said.