Criminal Inquiry Into Boeing Panel Blowout Expands

The Justice Department is sending subpoenas and using a recently convened grand jury in Seattle as it widens a criminal investigation into the door plug that blew off a Boeing 737 Max 9 jetliner in January, a person familiar with the matter said on Friday.

The detachment of the panel from the fuselage of an Alaska Airlines flight shortly after takeoff terrified passengers at 16,000 feet and required an emergency landing back at Portland International Airport in Oregon. A preliminary report by the National Transportation Safety Board said four bolts meant to secure the door plug in place were missing before the panel blew off.

This month, it was reported that the Justice Department had opened a criminal investigation of Boeing, which had reinstalled the door plug during maintenance in Renton, Wash., before delivering the plane to Alaska Airlines in October.

The subpoenas and use of the grand jury were reported earlier Friday by Bloomberg.

The midair incident on Jan. 5 led the Federal Aviation Administration to ground more than 170 Max 9 planes, which were then inspected for construction flaws. Boeing said it agreed with the F.A.A.’s decision and pledged to cooperate. The company has said safety is its top priority.

The Max 9s have since restarted flights, but questions remain about the malfunction. A grand jury could be asked to decide whether a criminal prosecution is warranted. A likely focus would be repairs to the Alaska Airlines plane’s rivets, which are often used to join and secure parts on planes, by workers at the Boeing plant in Renton.

The episode has brought a fresh round of scrutiny to Boeing. The company made grim headlines in 2018 and 2019 when two crashes of another 737 model, the Max 8, killed 346 people. Max 8 jets were grounded for almost two years. The company subsequently spent more than $2.5 billion to settle a criminal charge that Boeing had defrauded the F.A.A., and the company’s chief executive, Dennis Muilenburg, was fired.

Under his replacement, Dave Calhoun, Boeing’s stock has risen, though the company has struggled to meet airlines’ demands. Production of the 737 Max fell to about half of Boeing’s stated goals last year, as the company was bedeviled by supply chain issues with key suppliers and problems with fuselages.

Now, the company is facing far steeper challenges. Two days after the door plug incident, Mr. Calhoun sent a memo to employees stating that “while we’ve made progress in strengthening our safety management and quality control systems and processes in the last few years, situations like this are a reminder that we must remain focused on continuing to improve every day.”