Boeing chief executive Dennis Muilenburg faced criticism from US politicians on Tuesday at a packed hearing, as family members of victims from two Max 737 crashes watched on.
In his first appearance before Congress since the 737 Max aircraft was grounded in March, Mr Muilenburg apologised for the crashes and admitted to shortcomings, but defended Boeing's development of the model.
Senators from both parties showed clear dissatisfaction, with some close to rage.
Democratic Senator Tammy Duckworth, a former National Guard helicopter pilot who lost both legs during the Iraq War, was frank in her disapproval.
"Boeing is the company that built the Flying Fortress that saved Europe," said Ms Duckworth, who represents Illinois, home to Boeing's corporate headquarters.
"You have told this committee and you told me half-truths over and over again. You have not told us the whole truth and these families are suffering because of it."
Mr Muilenburg stuck to Boeing's longstanding position that the Max was developed under company procedures that were tested by time.
He defended it against charges that it cut corners on safety and was too familiar with the regulator, the Federal Aviation Administration.
Many analysts think the hearings will lead to Mr Muilenburg leaving the company in the foreseeable future, probably after the Max returns to service.
"That's not where my focus is," he said when asked if he would resign. "My focus is on the job at hand, focused on safety. And we're going to do everything we can to ensure safe flight."
Two Max 737 crashes within six months killed all 346 people aboard. They were a Lion Air flight on October 29, 2018 and an Ethiopian Airlines flight on March 10, 2019.
Nadia Milleron, who lost her daughter on the Ethiopian Airlines crash, said the company needed a shakeup, starting with Mr Muilenburg.
"He needs to resign," Ms Milleron said. "The whole board needs to resign. I expect him to stop putting the blame on the FAA and other people because that is what they always do. They don't take responsibility."
Many of the questions focused on Manoeuvring Characteristics Augmentation, an automated system that the pilots in both crashes were unable to control.
"We have learnt from both accidents and we've identified changes that need to be made to MCAS," Mr Muilenburg told the Senate commerce committee.
But Ted Cruz, a Texas Republican, heavily criticised the chief executive as he struggled to answer pointed questions about texts from Boeing pilot Mark Forkner to a colleague in 2016.
In the messages, Forkner discussed the "egregious" performance of the system during a simulation test and said that he "basically lied to the regulators".
Mr Muilenburg said Boeing's counsel shared the documents with the Justice Department in February, but he did not see the exchange until it was reported by media this month.
"I was made aware of existence of this kind of document," Mr Muilenburg told Mr Cruz. "I counted on counsel to handle this appropriately."
Mr Cruz replied: "That is passive voice. You're the CEO, the buck stops with you.
"How did your team not put it in front of you, run with their hair on fire and say, 'We have a real problem here?' How did that not happen and what does that say about the culture at Boeing?"
Senator Maria Cantwell, a Democrat from Washington state where the 737 Max is built, said the crisis showed that Boeing leadership was failing its employees.
"This isn't a question about line workers, this is a question about the corporate view from Chicago, and whether there is enough attention to manufacturing and certification," Ms Cantwell said.
"You should take offence to the fact that people say, 'It's a great company that's not being run correctly'."
Tuesday's hearing will be followed by a second session on Wednesday in the House transport committee.
Boeing is still aiming for regulatory approval for the Max in 2019, which many aviation experts still consider possible.
Senator Roger Wicker, a Mississippi Republican who chairs the committee, earlier told CNBC that he intended to scrutinise Boeing's processes but did not see anything that would prevent the Max from going back into service "fairly soon".
"I think this plane is eminently fixable," Mr Wicker said. "I don't think it's a hopeless cause."