Alaska Airlines Plane Appears to Have Left Boeing Factory Without Critical Bolts Regulators put limits on Boeing 737 MAX production; grounded MAX 9 jets have resumed flying after required inspections

By Andrew Tangel

Updated Jan. 29, 2024 12:03 pm ET You may also like Here’s a time line of what occurred after the aircraft’s midair incident. Photo: National Transportation/Planet Pix/Zuma Press

Bolts needed to secure part of an Alaska Airlines jet that blew off in midair appear to have been missing when the plane left Boeing’s BA -0.14%decrease; red down pointing triangle

factory.

Boeing and other industry officials increasingly believe the plane maker’s employees failed to put back the bolts when they reinstalled a 737 MAX 9 plug door after opening or removing it during production, according to people familiar with the matter.

The increasingly likely scenario, according to some of these people, is based partly on an apparent absence of markings on the Alaska door plug itself that would suggest bolts were in place when it blew off the jet around 16,000 feet over Oregon on Jan. 5.

They also pointed to paperwork and process lapses at Boeing’s Renton, Wash., factory related to the company’s work on the plug door. A hole from an Alaska Airlines plane’s blown-off door plug is covered. Photo: patrick t. fallon/Agence France-Presse/Getty Images

The National Transportation Safety Board has been conducting metallurgical analysis of the plug door but hasn’t released the results of the testing. Laboratory tests might show whether the bolts were in place or not there at all. An update in the NTSB probe is expected as soon as this week.

New evidence could later emerge before accident investigators reach final conclusions. It couldn’t be determined how many people were involved with work on the plug door at Boeing’s 737 factory.

Supplier Spirit AeroSystems delivered the 737 fuselage to Boeing’s factory with the door plug installed. The plug door itself was constructed in Spirit’s Malaysian factory, while the fuselage was assembled in Wichita, Kan.

Boeing opened or removed the door plug after the 737 MAX 9 jet’s fuselage arrived at the plane maker’s Renton, Wash., factory for final assembly, The Wall Street Journal and other news outlets have reported.

U.S. Sen. Tammy Duckworth (D., Ill.), chair of a key Senate panel on aviation safety, said she met with Boeing Chief Executive David Calhoun last week and discussed the probe into what went wrong.

“It is going to show that there has been lack of documentation when it comes with how and when those pins were installed or removed and whether or not they were reinstalled or not,” said Duckworth. “He assured me that they were going through that entire process to make sure that they are able to track on their aircraft when these things are happening.”

The Federal Aviation Administration last week put limits on Boeing’s production of 737 MAX jets, while also clearing the way for grounded jets to resume flying after airlines complete inspections.

Airlines have discovered loose hardware on some MAX 9 jets, and air-safety officials are probing Boeing’s manufacturing practices.

The Alaska accident has renewed scrutiny of problems with Boeing’s quality controls and supplier oversight, which have surfaced in recent years on various commercial and military aircraft. While the company has pushed to improve its factory operations, Calhoun has said Boeing must acknowledge “our mistake” in the Alaska accident.

The FAA’s increased regulatory scrutiny could slow Boeing deliveries and plans to ramp up production, as well as add to delays in certifying new 737 MAX variants awaiting regulatory approvals.

Sharon Terlep contributed to this article.

Write to Andrew Tangel at andrew.tangel@wsj.com