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 that the FAA gave Congress misleading answers when it asked about FAA employee training.
The head of the office says the FAA's actions put the flying public at risk.
The agency said Tuesday that it told President Donald Trump and Congress about its findings, which started with a complaint from a whistleblower.
The agency'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.