U.S. aviation safety regulators found Boeing Co. failed to comply with manufacturing quality control requirements on “multiple” occasions, according to an audit launched in response to response a harrowing near-disaster involving a new Alaska Airlines 737 Max 9 jet in January. 

The shortfalls were found at both Boeing and Spirit AeroSystems Holdings Inc., which makes most of the 737’s fuselage, the Federal Aviation Administration said in a statement on March 4.  

The U.S. regulator sent more than a dozen inspectors into Boeing’s factories as well of those of Spirit after a fuselage panel exploded out of the airborne Alaska Airlines jet on January 5. Their findings were released days after the FAA issued a scathing review of deficiencies in Boeing’s safety culture, and the agency gave the company 90 days to draft a comprehensive plan to fix those shortcomings.  

“The FAA identified non-compliance issues in Boeing’s manufacturing process control, parts handling and storage, and product control,” the agency said in the release. 

The agency didn’t release the full audit report or detail of the alleged violations, citing its ongoing probe of quality issues linked to the dramatic incident. Still, the findings add to the pressure facing the manufacturing giant to tighten up its processes.

The six-week FAA audit “found multiple instances where the companies allegedly failed to comply with manufacturing quality control requirements,” the agency said.

The FAA’s findings follow a separate report by the National Transportation Safety Board that found the Alaska jet was delivered without four bolts meant to hold the so-called door plug in place. 

The panel was opened at Boeing’s factory to perform repairs on the plane and photos showed it was reinstalled without those bolts, the NTSB said. Investigators have not yet concluded how the lapse occurred. 

The audit comes as Boeing makes its biggest-ever shift away from outsourcing by potentially reintegrating its former division, Spirit. The FAA and airlines are also ratcheting up scrutiny of the U.S. planemaker’s practices within its factories and its control over quality at suppliers.

While the FAA has allowed Boeing to keep building its cash-cow jetliner, the agency has capped 737 production rates until it’s satisfied the company has quality under control. 

FAA Administrator Mike Whitaker has said that the agency may broaden its review if problems are found elsewhere. He also told U.S. lawmakers that the agency personnel may maintain a larger presence at Boeing’s plants over the longer term.  

A separate FAA investigation is underway to determine whether Boeing had adequate controls in place to ensure that planes leaving its factory strictly conform to their agency-approved design. Bloomberg reported on Feb. 29 that the Justice Department is examining the blowout in light of a deferred prosecution agreement reached in the wake of two deadly 737 crashes that led to a grounding of the model in 2019. The single criminal count was due to expire days after the Alaska Air incident. 

Boeing, for its part, has added more frequent pauses to its 737 manufacturing to address missing or incomplete parts, stepped up inspections and sent a small army of workers to assist Spirit in bolstering its quality. Bloomberg News and others reported last week that the company is in talks to acquire Spirit AeroSystems, bringing the fuselage maker back into Boeing’s fold after a 2005 split. 

In a statement, Boeing reiterated its February 28 commitment to deliver a comprehensive plan to address the agency’s recent findings and lessons from its recent internal factory pauses to focus on quality.

Spirit didn’t immediately respond to requests for comment on the FAA release.