The Justice Department has begun a criminal investigation into Boeing after a panel on one of the company’s planes blew out on an Alaska Airlines flight in early January, a person familiar with the matter said.

The airline said it was cooperating with the inquiry. “In an event like this, it’s normal for the D.O.J. to be conducting an investigation,” Alaska Airlines said in a statement. “We are fully cooperating and do not believe we are a target of the investigation.” Boeing had no comment.

On Jan. 5, a panel on a Boeing 737 Max 9 jet operated by Alaska Airlines blew out in midair, exposing passengers to the outside air thousands of feet above ground. There were no serious injuries resulting from that incident, but it could have been catastrophic had the panel blown out minutes later, at a higher altitude.

The panel is known as a “door plug” and is used to cover a gap left by an unneeded exit door. A preliminary investigation by the National Transportation Safety Board suggested that the plane may have left Boeing’s factory without the plug bolted down.

The investigation was first reported by The Wall Street Journal.

This is a developing story. Please check back for updates.