U.S. air safety regulators found “dozens of problems” at facilities owned by Boeing and one of its key suppliers after a six-week audit of the production of the 737 Max jet, according to The New York Times.

The Federal Aviation Administration started the probe after a door panel blew off a 737 Max 9 flight on Alaska Airlines in early January, an incident that has attracted intense scrutiny of Boeing’s quality-control practices.

FAA auditors found that out of 89 product audits that were conducted, Boeing passed 56 tests and failed 33 of them, according to the report.

During the six-week audit, the FAA also conducted 13 product audits that focused on Spirit AeroSystems, which makes fuselages for the Boeing 737 Max — of those, only six audits resulting in passing grades, and seven failed, the NYT said.

Click here for CNBC’s full story on the audit.