US lawmakers have accused Boeing of engaging in a “pattern of deliberate concealment” as it sought approval for its 737 Max 8 model to fly.
The accusation came as Boeing chief executive Dennis Muilenburg was quizzed by the Senate Commerce Committee.
Senators said they had serious concerns that Boeing put profits over safety as it rushed to get clearance.
Two deadly 737 Max 8 crashes killed a total of 346 people. Mr Muilenburg admitted the firm had made “mistakes”.
“We have learned from both accidents and identified changes that need to be made,” he said.
In October last year, a Boeing 737 Max operated by Lion Air crashed, killing all 189 people on board.
Five months later an Ethiopian Airlines plane crashed, killing 157, after which the entire 737 Max fleet was grounded.
‘Casualness and flippancy’
Lawmakers accused Boeing of being aware of problems in the automated control system in the 737 Max 8, known as MCAS, which has been identified as a factor in both accidents.
Senator Roger Wicker said messages between Boeing staff that discussed problems in the MCAS test system betrayed “a disturbing level of casualness and flippancy”.
Senator Richard Blumenthal said Boeing had engaged in a “pattern of deliberate concealment”.
Boeing provided the messages to the committee ahead of the testimony.
Mr Muilenburg said he became aware of them only recently and could not elaborate on the exchange.
Senators also criticised the regulatory process, saying there was too much “cosiness” between the firm and safety officials at the Federal Aviation Administration (FAA).
Mr Blumenthal described the US certification process as “absolutely broken”.
Mr Muilenburg said the firm supported “strong oversight” but declined to support increasing the authority of the FAA, which has been criticised for delegating too much of its oversight to company officials.
Mr Muilenburg said safety is enhanced by tapping industry technical expertise.
The company also disputed the characterisation of its relationship with regulators as “cosy”.
“It’s not a cosy relationship. It’s a professional relationship,” said Boeing’s chief engineer John Hamilton.
Since the grounding of the 737 Max fleet, Boeing has said it is fixing software and has overhauled its review procedures.
But senators said the continued delays in re-certification cast serious doubt on the initial approval.