The chief executive officer of Boeing on Sunday said that the United States-based aircraft maker had made a mistake in installing a faulty cockpit warning system on its 737 MAX planes, Reuters reported. Dennis Muilenburg’s admission came after two fatal crashes over the last year.

In March, 157 people died when Ethiopian Airlines flight JT610 crashed minutes after takeoff. In October last year, 189 people died when Lion Air’s flight ET302 crashed off the coast of Indonesia. Both crashes involved the 737 MAX model. In April, Boeing announced plans to cut back production of its 737 MAX aircraft after several countries grounded the aircraft following the crashes.

Muilenburg said on Sunday that Boeing failed to communicate “crisply” with regulators and customers, and admitted that it will take a long time for the plane maker to regain consumer confidence. However, he defended the company’s broad engineering and design approach to the Boeing 737 MAX planes.

The chief executive said he expects the 737 MAX to return to service this year. Muilenburg added that 90% of the aircraft’s customers have taken part in in simulator sessions with its upgraded MCAS software. “Clearly, we can make improvements, and we understand that and we will make those improvements,” he said.

Muilenburg said the company is fully supporting the criminal investigation the US Department of Justice has initiated into the two crashes.

‘Pilots not to blame for Ethiopian Airlines crash’

Meanwhile, Ethiopian Airlines Chief Executive Officer Tewolde GebreMariam told BBC on Sunday that pilots were not to blame for the crash in March. He was responding to US Congressman Sam Graves, who said at a hearing in Washington DC last month that “facts in the preliminary report reveal pilot error as a factor”.

GebreMariam told the BBC that Graves “did not have the facts in hand”. The preliminary report into the crash “made it abundantly clear the pilots followed the procedures properly”, the chief executive officer added. “It’s a global fact that the aircraft has a problem, that’s why it’s grounded and Boeing is making modifications,” he said. “People who’ve made those comments should ask themselves, ‘Why on earth have they grounded 380 airplanes over the world?’ The facts speak for themselves.”