Boeing’s chief executive, Dennis Muilenburg, faced the anger of members of Congress in Washington over the failure of the aircraft maker and US regulators to identify and correct flaws in the design of the 737 Max jet that led to two crashes, killing 346.

Muilenburg, who was forced to step down as Boeing chairman earlier this month after emails suggesting Boeing test pilots knew about defects in an anti-stall system but failed to alert regulators, opened his testimony with an apology to the family members of crash victims.

“We are sorry, truly and deeply sorry,” Muilenburg said. “As a husband and father, I am heartbroken by your losses.”

Muilenberg was appearing at the first of a series of congressional committee hearings. Tuesday’s occurred on the first anniversary of the Lion Air flight 610 crash in Indonesia that killed 189 people. In March, after an Ethiopian Airlines 737 Max crashed, killing 157 people, the 737 Max was grounded worldwide, and Muilenburg pledged such accidents would not happen again.

But he was subjected to withering questioning from US politicians from both sides of the political aisle, in the first of several planned hearings and further investigations into Boeing’s conduct over the top-selling jet.

Boeing was accused of putting profits over safety and developing a cosy relationship with regulators that permitted the company to rush the 737 Max, Boeing’s most profitable model, into service.

“Both of these accidents were entirely avoidable,” the Mississippi senator Roger Wicker, a Republican, said. “We cannot fathom the pain experienced by the families of those 346 souls who were lost.”

Last week, an Indonesian report into the Lion Air crash criticized the design of the anti-stall system that left pilots fighting for control, as well as “deficiencies” in the flight crew’s communication and manual control of the aircraft.

The Ethiopian Airlines crash led to the grounding of the aircraft. That decision is estimated to have cost Boeing as much as $9bn.

At the hearing, the Connecticut Democratic senator Richard Blumenthal sharply accused Boeing of engaging in “a pattern of deliberate concealment”, noting that Boeing’s 1,600-page pilot’s manual mentions the so-called MCAS anti-stall system just once. Blumenthal accused Muilenberg and Boeing of supplying “flying coffins as a result of Boeing deciding to conceal MCAS from pilots”.

At issue are recently disclosed internal instant messages that Boeing had not previously handed to committee investigators. The messages, sent by Boeing’s chief test pilot Mark Forkner in 2016, complained of “egregious” erratic behavior in flight simulator tests of the MCAS system, and referred to “Jedi mind tricks” to persuade regulators to approve the plane.

Muilenburg claimed he was not fully briefed on the details of the messages until a “couple of weeks ago” despite the company knowing of the exchange before the Ethiopian airlines crash.

The Texas Republican senator Ted Cruz called the test pilot’s exchange “shocking” and accused Boeing of withholding knowledge of the systems faults from regulators.

Cruz said: “How come your team didn’t come to you with their hair on fire, saying, ‘We’ve got a real problem here’? What does that say about Boeing? Why did you not act before 346 people died?”

Lawmakers accused Boeing of selling safety as an “add-on feature”, referring to a warning light that advises pilots of any discrepancy in the aircraft’s pitch, which was sold as an add-on rather than included as standard.

“If you want to be the leader in aviation manufacturing you have to be the leader in safety,” offered the Washington senator Maria Cantwell, the committee’s top Democrat.

The committee has said it plans to change the program that gave Boeing, rather than regulators, authority to sign off on aspects of the jet.

“We don’t ‘sell’ safety, that’s not our business model,” Muilenburg claimed under questioning. “We have learned that we’ve made mistakes, and there are things we can improve. We take responsibility for that, we own that, we’ve made fixes going forward.”

As the first Boeing official to testify on Capitol Hill about the crisis engulfing the company, Muilenburg said that since the 737 Max was grounded, the company has conducted extensive testing with updated software.

Several other inquiries are also expected to report soon, including an international panel convened by the Federal Aviation Authority, the US regulator, to recommend changes to the way planes are certified. There is also a looming criminal investigation by the US justice department.

Asked if Boeing could have done more after the first 737 Max crash, Muilenburg said: “I think about that decision over and over again. If we knew then what we know now we would have made a different decision.”

The Democratic Illinois senator Tammy Duckworth, a former military pilot, questioned why Boeing did not disclose more details about anti-stall system’s lack of safeguards.

“You have told me half-truths over and over again,” Duckworth said. “You have not told us the whole truth and these families are suffering because of it.”

Duckworth said the pilots did not know enough about the anti-stall system. “You set those pilots up for failure,” she said.

Reuters contributed to this report