Members of the US Senate grilled Boeing CEO Dennis Muilenburg on the first anniversary of a Lion Air crash involving the 737 Max, accusing the company of putting profit before safety.

The October 2018 accident killed all 189 people on board, while a second crash involving a Max operated by Ethiopian Airlines in March killed 157 passengers and crew, leading to authorities around the world issuing a grounding order for the aircraft.

During a hearing by the Senate Committee on Commerce, Science and Transportation, lawmakers said they had concerns that Boeing had engaged in “a pattern of deliberate concealment” during the approval process for the 737 Max and its Manoeuvring Characteristics Augmentation System (MCAS).

Chairman senator Roger Wicker said the committee needed “to know if Boeing and the FAA [Federal Aviation Administration] rushed to certify the Max”. In particular, he pointed out criticism that testing of the MCAS may have ‘misjudged’ how pilots would react because the number of warnings and alerts the crew involved in the crashes faced were not included in simulator tests.

Wicker’s opening statement included details of email correspondence dating from as early as 2015 between the Max’s former chief technical pilot Mark Forkner and FAA personnel released earlier this month that “reflect a disturbing level of casualness and flippancy that seem to corroborate these criticisms”.

Along with the emails, Boeing provided lawmakers with transcripts of instant messages sent between employees as the 737 Max was being certified in 2016, in which one pilot said he had “basically lied to the regulators” after facing trouble during tests.

Senators also questioned the US’s regulatory process and the level of “cosiness” between the FAA and Boeing, something the firm’s chief engineer John Hamilton strongly denied.

In response to the criticisms, Muilenburg – who was recently stripped of his title as chairman but is still the company’s chief executive – admitted Boeing had made mistakes but stressed the manufacturer has “learned from both accidents and identified changes that need to be made”.

Boeing is still working on a software update to fix a potential issue with the MCAS that could erroneously trigger the system to push the nose of the plane down during take-off, which has been named as a contributing factor in both crashes.

The manufacturer maintains its belief that the aircraft will return to service soon, but senators at today’s hearing said the delays to recertification cast doubt on the aircraft’s initial approval.

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