Boeing apologized following two crashes and acknowledged falling short in communications with regulators

The head of Boeing's embattled 737 MAX program plans to retire, the company said on Thursday, just as it gears up to persuade regulators to return the plane to the skies after two deadly crashes.

It was the most high profile departure of a senior executive since the aircraft was grounded in mid-March following two crashes that claimed 346 lives.

Eric Lindblad, who has led the MAX program since August 2018, will step down and work with his successors on a transition, Commercial Airplanes President Kevin McAllister said in a staff memo.

Boeing apologized following the two crashes and acknowledged falling short in communications with regulators. But top officials, including chief executive Dennis Muilenburg, have kept their jobs amid the crisis.

"These are unprecedented times for us, as our primary focus remains the safe return of service for the 737 MAX and driving quality and safety in all that we do," McAllister said.

The company has been widely criticized over its development of the 737 MAX, which included a flight handling system called the Maneuvering Characteristics Augmentation System that has been seen as a factor in both crashes.

McAllester praised Lindblad for "strong leadership and timeless drive" since assuming the 737 program less than a year ago.

Lindblad "shared with me his desire to retire last year, and we will now begin to embark on a thoughtful and seamless transition plan," McAllister said.

Mark Jenks, a 36-year company veteran, will replace Lindblad. Jenks has been leading Boeing's effort to develop a new midsized commercial plane. The memo did not specify the timing of the transition.

McAllester also said Boeing executive Mike Sinnett, an executive in product strategy and future airplane development, will assume Jenks' duties while continuing work to restore the MAX to service.

Sinnett "will also continue to play a pivotal role in our stakeholder and customer outreach efforts on the MAX certification and return to service efforts," McAllister said.

Boeing has developed a software upgrade for the MCAS. But the jet has not yet been cleared by regulators to resume flights.

The Federal Aviation Administration late last month identified a fresh problem during simulator testing, further clouding the outlook for the plane's return to service.