Dennis Muilenburg is out as CEO of Boeing, the company announced on Monday. Multiple news organizations are reporting that Boeing's board decided to fire Muilenburg over the weekend.

Muilenburg's departure caps a disastrous year for the aerospace giant. Two deadly crashes of Boeing's new 737 MAX—one in October 2018, the second in March 2019—forced airlines around the world to ground their planes. Investigations revealed that the crashes were due to flaws in the design of the aircraft's Maneuvering Characteristics Augmentation System (MCAS) software.

This software tries to help the pilot provide a safer, smoother ride. But in both crashes, a malfunctioning sensor caused the software to mistakenly believe the aircraft was stalling. It then pushed the plane's nose too far down, ultimately leading to a crash. Pilots either didn't realize the MCAS system was malfunctioning or couldn't figure out how to turn it off. Boeing has faced criticism for providing pilots with too little training and documentation about how the new controls differ from previous 737 models.

Boeing had hoped to push out a software fix within weeks after the March crash. But weeks stretched into months after peer reviewers raised concerns about the proposed fix. Boeing must get approval from the Federal Aviation Administration (FAA) to push out an update to the MCAS software, and the FAA has faced its own criticism for lax oversight during development of the 737 MAX. This has created a tense relationship between Boeing and the FAA.

As 737 MAX planes remain grounded around the world, Boeing's airline customers have lost millions of dollars in ticket sales. Last week, Boeing announced it would suspend production of the 737 MAX in January 2020.

Then, this weekend, Boeing's Starliner spacecraft malfunctioned during an orbital test. Once it separated from its rocket, the vehicle was supposed to fire its Orbital Maneuvering and Attitude Control engines to bring it into the right orbit to rendezvous with the International Space Station. But it failed to do so. By the time controllers on the ground realized what had happened, the Starliner didn't have enough fuel to reach the ISS and then return safely to Earth. It returned to Earth on Sunday without completing its docking mission.

Boeing's board decided to fire Muilenburg on Sunday, shortly after the Starliner mishap, according to The New York Times. He will be replaced by Boeing Chairman Dave Calhoun next month.

Boeing's stock is down about 20 percent since the March crash—though it rose about 2 percent on news of Muilenburg's ouster.