Renton, Washington - The Federal Aviation Administration on Monday said it found "multiple" issues with aircraft maker Boeing's production practices during an investigation launched after a fuselage panel blew out midair on a 737 MAX flight.

The FAA said it found cases where Boeing and parts supplier Spirit AeroSystems "allegedly failed to comply with manufacturing quality control requirements."

"The FAA identified non-compliance issues in Boeing's manufacturing process control, parts handling and storage, and product control," the US regulator said, adding that the investigation into Boeing and the fuselage supplier Spirit Aerosystems was ongoing.

The investigation comes after an incident in early January when a part of the fuselage of a virtually new Boeing 737-9 MAX with more than 170 people on board tore out of the plane body at seat row 26 shortly after take-off. No-one was seriously injured, and the two seats directly by the rip were luckily empty.

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The National Transportation Safety Board (NTSB) said the detachment of the panel was due to crucial bolts being removed during the manufacturing process at Boeing's Renton facility, suggesting they may not have been reinstalled.

Boeing had to stop deliveries of the aircraft model for weeks at a time and has been given 90 days to come up with a comprehensive action plan addressing its quality control issues and complying with the FAA's safety standards.

Ed Clark, vice president of the 737 Max program and general manager at the Renton facility, has been forced to leave his position.