The chairman of the House Transportation Committee said Wednesday that an FAA analysis of the Boeing 737 MAX jetliner performed after a fatal crash previous year predicted "as many as 15 future fatal crashes within the life of the fleet".
Noting that there is no clear timeline for when the 737 Max will be re-certified, Dickson said that there are 10 to 11 milestones left to complete before it can be approved. He also admitted that the authority should have grounded the fleet after the first of the two crashes that costed the lives of 346 people.
Once the FAA gives 737 Max approval, American will need at least 30 days to prepare the jets and its pilots for commercial flights, airline and union officials have said.
He said the report "should have rung alarm bells and apparently it didn't and we're going to be getting into that".
Lawmakers questioned Dickson about an internal FAA analysis produced after the first fatal crash on a Lion Air flight in Indonesia previous year that suggested serious risks of crashes over the life of the airplane and questioned why that did not prompt more aggressive action.
The agency also issued guidelines to flight crews worldwide on how the respond to a problem with MCAS, an automated system that pilots were unable to control during the Lion Air crash.
During Wednesday's hearing, FAA administrator Stephen Dickson confirmed the agency will continue to maintain oversight of the aircraft company.
"Obviously the result was not satisfactory", said Mr Dickson, who was put in charge of the FAA in the summer, after the accidents.
Even as Dickson sought to reassure the lawmakers, a former Boeing employee who repeatedly warned company officials about the working conditions at the Renton, Wash., plant where the aircraft was being built, urged lawmakers to investigate conditions at that plant.
After Dickson testified, he spoke to some of the family members of the crash victims, who pressed him to make sure there is never a similar 737 MAX crash.
The FAA said Dickson recommended to Muilenburg "that Boeing's focus should be on the quality and timeliness of data submittals for FAA review".
DeFazio said it was not clear how widely the FAA's internal risk analysis was distributed to the agency and whether officials at a key airworthiness committee viewed the document. Boeing declined to comment this week on that forecast, deferring to the FAA.
The DC hearing began with a discussion of a November 2018 internal FAA review which, following the first crash, found that the plane had a high likelihood of future crashes.
He said the accidents showed problems with "fragmented and inadequate" communications at the agency that inhibited the agency's ability to comprehensively assess safety during certification.