Washington DC - Boeing chief executive Dave Calhoun on Tuesday apologized to the relatives of the victims of the fatal crashes involving the aircraft maker's 737 airplanes in 2018 and 2019 during a hearing at the US Senate.

A total of 346 people lost their lives in the accidents.

"We are deeply sorry for your losses," Calhoun said on Tuesday, addressing several of the victims' relatives present.

"Nothing is more important than the safety of the people who step on board our airplanes. Every day, we seek to honor the memory of those lost through a steadfast commitment to safety and quality."

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The accidents involving 737 MAX 8 aircraft belonging to Indonesian airline Lion Air and Ethiopian Airlines were caused by problems with flight control software.

The system, known as MCAS, was designed to help pilots control the aircraft in certain situations. However, in both cases, the pilots were surprised by the software's irregular intervention.

Boeing previously acknowledged that it had not accurately communicated the extent of pilot training required to operate the software to the US Federal Aviation Administration (FAA).

Following the second accident, 737 Max aircraft were grounded worldwide for more than 18 months and were only authorized to fly again after technical improvements had been made.