Investigators say many Federal Aviation Administration inspectors who worked on pilot-training standards for the grounded Boeing 737 Max and other planes were themselves unqualified and insufficiently trained.
The U.S. Office of Special Counsel also says the FAA gave a Senate committee misleading answers when the panel asked about the issue.
"The FAA's failure to ensure safety inspector competency for these aircraft puts the flying public at risk," Special Counsel Henry Kerner said Tuesday.
Kerner's office notified President Donald Trump and Congress about its findings, which started with a complaint from a whistleblower.
The FAA said in a statement that it was reviewing Kerner's finding.
"We remain confident in our representations to Congress and in the work of our aviation safety professionals," the FAA said.
The special counsel's disclosures are another setback for the FAA, which is already under scrutiny for its certification of the 737 Max. According to published reports, senior FAA officials did not understand a key flight-control system that was later implicated in two deadly crashes.
The FAA determined that 16 of 22 inspectors had not finished their formal training and of the 16, 11 did not hold a flight-instructor license, a requirement for the job. But, the FAA told Congress this spring, none of the unqualified inspectors worked on training standards for the Max.
The special counsel said that was not true. Based on information from the whistleblower and other evidence, Kerner said, there were "undertrained" inspectors in the Max program and it is likely they were neither qualified to certify other pilots to fly nor to recommend how pilots should be trained for procedures and maneuvers on the plane.
The Max remains grounded after two crashes killed 346 people. Boeing is nearing completion of changes that it hopes will persuade regulators to let the plane fly again, and pilot training has emerged as a key issue.
Some safety advocates and relatives of passengers killed in the crashes demand that pilots be trained on flight simulators before the plane is put back in service — a requirement that would delay the plane's return by weeks or months. Boeing believes that training on the updated flight-control system can be done on tablet computers and FAA technical advisers agree, although the agency has not made a final decision.