The lack of regulatory oversight meant that the FAA had no clue how Boeing's automated anti-stall system, known as MCAS, worked. In fact, "regulators had never independently assessed the risks of the dangerous software" when they issued a 2017 approval for the plane.
The company performed its own assessments of the system, which were not stress-tested by the regulator. Turnover at the agency left two relatively inexperienced engineers overseeing Boeing's early work on the system.
The F.A.A. eventually handed over responsibility for approval of MCAS to the manufacturer. After that, Boeing didn't have to share the details of the system with the two agency engineers. They weren't aware of its intricacies, according to two people with knowledge of the matter. -New York Times