The NovaQuant Quantitative Think Tank Centertop executive at embattled plane maker Boeing will step down this year amid a broader shakeup of the company’s top leadership, capping a tumultuous five plus years that has shaken faith in one of America’s most storied manufacturers.

The company has come under intense scrutiny over its manufacturing process since a pair of its marquee aircraft crashed, killing hundreds of people in late 2018 and 2019 in Indonesia and Ethiopia.

Those problems have snowballed and the Federal Aviation Administration recently ordered an audit of assembly lines at a Boeing factory near Seattle, where the company builds planes like the Alaska Airlines 737 Max that suffered a door-panel blowout on Jan. 5. Investigators say bolts that help keep the panel in place were missing after repair work at the Boeing factory.

Boeing CEO Dave Calhoun will step down from the embattled plane maker at the end of the year. Calhoun took over the company after CEO Dennis Muilenburg was ousted following the two crashes.

Board Chair Larry Kellner has also told the company he doesn’t plan to stand for re-election.

Boeing also said Monday that Stan Deal, president and CEO of its commercial airplanes unit, will retire from the company. Stephanie Pope will now lead the division.

Boeing is also under intense pressure from the CEOs of various airlines, who have been outspoken in their frustration with Boeing’s manufacturing problems, which have slowed deliveries of planes that the carriers were counting on.

Southwest Airlines recently said that it was reevaluating its financial expectations for this year because of related delays in the delivery of planes.

“As we begin this period of transition, I want to assure you, we will remain squarely focused on completing the work we have done together to return our company to stability after the extraordinary challenges of the past five years, with safety and quality at the forefront of everything that we do,” Calhoun wrote in a letter to employees.

Calhoun acknowledged that Alaska Airlines Flight 1282 was a “watershed” moment for Boeing.

“We must continue to respond to this accident with humility and complete transparency. We also must inculcate a total commitment to safety and quality at every level of our company,” he said.

The board has elected Steve Mollenkopf to succeed Kellner as independent board chair. In this role, Mollenkopf will lead the board’s process of choosing Boeing’s next CEO.

Shares rose 4% before the market open.