The new version of the decades-old 737 was approved with a vulnerable flight-control system and flaws in its fuel tank because Boeing and Federal Aviation Administration management overruled front-line workers, the report charged.
Elwell said he expects Boeing to complete its work "in the next week or so", after which the FAA will analyze the software changes and conduct test flights.
Acting FAA administrator Daniel Elwell said he was "not aware of an internal assessment that reaches that conclusion".
At the same time Wednesday, the Senate Commerce Committee is expected to hear from Stephen Dickson, a former airline pilot and Delta Air Lines executive whom President Donald Trump nominated to head the FAA on a permanent basis.
During the two-hour questioning of Elwell by the House aviation subcommittee, lawmakers pressed him on the FAA's reliance on designated Boeing employees during the planes' certification process.
"The FAA has a credibility problem", declared the subcommittee chairman, Rick Larsen.
The sale of Boeing's 737 for 2019 dropped by 171 units in April as the plane-maker adjusted its orders after Jet Airways shut its operations over financial distress, Bloomberg reported. He said Congress must help make the public feel safe about flying because "if they don't fly, airlines don't need to buy airplanes", and "then there will be no jobs" in aircraft manufacturing.
House lawmakers on Wednesday attempted to get to the bottom of Boeing's troubled 737 Max airliners, asking aviation leaders about an update on the grounded fleet and about how the planes were certified to fly years ago. Those accidents killed almost 350 people.
"We scan and filter every one of those flights for evidence that there were MCAS. anomalies in the USA fleet", he said, again reiterating that the FAA found no reports of that kind.More news: Sudan's Bashir charged over killings of protesters
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Are the safety issues unique to just the 737 Max, or all Boeing planes?
The audio, obtained by CBS News, captured American Airlines pilots demanding more information about the anti-stall system, known as MCAS, during a tense meeting with Boeing officials in November.
Missing Documents Transportation and Infrastructure Chairman Peter A. DeFazio, D-N.Y., said the FAA has begun providing the committee with documents requested surrounding the agency's certification process and handling of the 737 Max after the accidents, but that Boeing has not yet provided "a single" document.
Asked by Rep. Sharice Davids, a Democrat from Kansas, whether the FAA moved too quickly to certify the plane for flight, Elwell outlined the five-year process that ended in 2017, including almost 300 test flights, and said it wasn't out of the ordinary.
According to the reports, the pilots were particularly concerned about the MCAS anti-stall system that investigators in both Indonesia and Ethiopia have blamed for the crashes.
Boeing has said its software upgrade and associated pilot training will add layers of protection to prevent erroneous data from triggering the system called MCAS. They encouraged quick activity after the principal lethal 737 Max crash off Indonesia in October.
Boeing is changing MCAS to make it less powerful, and to link the system to two sensors instead of one. The Congress meeting also prompted Elwell to identify the company's mistakes or failures that allowed for errors in the jets' MCAS system.
"No one has yet to conclude that the sole cause of this was this function on the airplane", Boeing vice-president Mike Sinnett told the meeting. Boeing officials did not testify.