Muilenburg, who was stripped of his title as Boeing's chairman by the board this month, will also testify before the US House of Representatives Committee on Transportation and Infrastructure on Wednesday.
"How frequently are new automated systems left out of the training manuals that you give to pilots", Senator Amy Klobuchar asked.
On Tuesday, Muilenburg denied Boeing's initial statements about the investigative findings from the Lion Air crash sought to shift blame onto pilots. Richard Blumenthal (D-Conn.).
The pilot said "this was egregious", but "I basically lied to regulators (unknowingly)", according to the message transcript. Passengers "never had a chance". Richard Blumenthal, D-Conn. "They were in flying coffins as a result of Boeing deciding it was going to hide MCAS from pilots".
Despite these apologies, committee members loudly voiced their concerns about the way Boeing brought the 737 MAX to market and how it has handled things since the crashes and subsequent grounding.
"How did you not in February set out a 9-alarm fire to say, we need to figure out exactly what happened, not after all the hearings, not after the pressure, but because 346 people have died and we don't want another person to die", he said.
The company saw capacity decline year over year for the first time in several years, but expects capacity growth of three per cent in the fourth quarter, said chief commercial officer Lucie Guillemette.
He told senators Tuesday that Boeing had always trained pilots to respond to the effect caused by an MCAS failure - a condition called runaway trim - which also can be caused by other problems.
In early stages of Lion Air flight 610 crash, it was discovered that there was a disagreement of approximately 20° between the left and right AoA sensors on the plane. Tuesday's hearing represents Boeing's broadest acceptance of responsibility that it made mistakes, though Muilenburg's written testimony ahead of the hearing did not describe in detail what those mistakes were.
The 737 Max was grounded in March, following the second accident.
The Boeing jets were grounded earlier this year following two fatal crashes in five months.
Senate Commerce Committee Chairman Roger Wicker told Reuters last week that the 737 MAX "won't fly unless 99.9% of the American public and American policymakers are convinced that it's absolutely safe". When they trickled into the room holding the photos, Muilenburg turned in his seat to look at them.
Boeing Co chief executive Dennis Muilenburg has faced intense grilling by USA lawmakers over what the company knew about its stall-prevention system linked to two deadly crashes, and about delays in turning over internal 2016 messages that described erratic behaviour of the software in a simulator.
USA airlines have cancelled flights into January and February because of the grounding and the Federal Aviation Administration is not expected to approve the 737 MAX's ungrounding until December at the earliest. It's an approach the FAA has followed for many years. He admitted mistakes were made in communications about the MCAS anti-stall system and in delayed disclosures to the FAA.
The committee didn't get an answer to that question.
Doug Taylor, an analyst with Canaccord Genuity, highlighted how "the company has been able to effectively pass the added costs through to customers".
"In the months since the accidents, there has been much criticism of Boeing and its culture". "We understand that we have important work to do for the world", said Muilenburg.
"Clearly there was a breakdown in the system somewhere and clearly changes needed to be made", Wicker said. Cantwell asked Hamilton whether it was a mistake for Boeing not to test a failure mode similar to the scenarios faced by pilots in the crashes. He added: "We also know we can and must do better".
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