Boeing's top-selling 737 MAX plane has been grounded since mid-March following two deadly crashes.

Boeing unveiled a shift to its leadership structure on Friday as it manages the 737 MAX crisis, announcing that Dennis Muilenburg will remain chief executive but step down as chairman.

The company said splitting the roles would allow Muilenburg to focus full time on running the company "as it works to return the 737 MAX safely to service" while ensuring full support to customers sharpening Boeing's focus on safety.

"This decision is the latest of several actions by the board of directors and Boeing senior leadership to strengthen the company's governance and safety management processes," it said in the statement.

The company named David Calhoun, currently lead independent director, to serve as non-executive chairman.

Calhoun said the "board has full confidence in Dennis as CEO and believes this division of labor will enable maximum focus on running the business with the board playing an active oversight role."

Boeing's top-selling 737 MAX plane has been grounded since mid-March following two deadly crashes that killed 346 people.

Boeing is targeting regulatory approval for the plane's return to service this year following upgrades, but the aerospace giant has noted government authorities will have the final say.

A report Friday by international aviation regulators criticized the US Federal Aviation Administration's certification of the MAX.

It said the agency lacked the necessary manpower and expertise to evaluate key flight-handling changes on the plane and also delegated too much to Boeing staff.