The Federal Aviation Administration said on Monday that a six-week audit of Boeing and one of it key suppliers, Spirit AeroSystems, found “multiple instances” in which the companies failed to comply with quality-control requirements.
As part of the audit, which looked at production of the Boeing 737 Max, the F.A.A. said that it had “identified noncompliance issues in Boeing’s manufacturing process control, parts handling and storage, and product control.” The regulator did not publicly release further details.
The F.A.A. initiated the audit after a door panel came off a 737 Max 9 jet while at about 16,000 feet in early January, raising new questions about quality-control practices at Boeing and Spirit, which makes the fuselage, or body, of the 737 Max.
Boeing did not immediately comment. A spokesman for Spirit, Joe Buccino, said the company was reviewing the findings and was “in communication with Boeing and the F.A.A. on appropriate corrective actions.”
The episode involving the door panel, known as a door plug, occurred on an Alaska Airlines flight shortly after it took off from Portland, Ore., on Jan. 5. The F.A.A. quickly grounded similar Max 9 jets, though the planes were allowed to return to service later that month after being inspected.
In a preliminary report last month, the National Transportation Safety Board said that four bolts used to secure the door plug had been removed from the jet at Boeing’s factory in Renton, Wash. The report suggested that the bolts may not have been reinstalled before the plane entered service.
The F.A.A.’s audit was one of several steps that the regulator took in the aftermath of the door-plug episode to step up scrutiny of Boeing’s manufacturing processes. The agency also opened an investigation into whether the plane maker failed to ensure that its products were safe and conformed to their approved design, and it barred the company from increasing production of the 737 Max series until quality-control issues are addressed.
Last week, the F.A.A. gave Boeing 90 days to develop a plan to improve its quality-control practices. The plane maker has already announced a leadership shake-up in its commercial airplanes unit, and it said on Friday that it was in talks to acquire Spirit, which it spun out nearly two decades ago.