The United States opens a criminal investigation into the explosion of a Boeing 737 MAX plane during flight Transport News

The investigation comes amid increasing scrutiny of Boeing's safety record following fatal accidents in 2018 and 2019.

US prosecutors have opened a criminal investigation into the mid-flight explosion of an Alaska Airlines Boeing 737 Max plane, according to US media reports.

The Wall Street Journal and Washington Post reported on Saturday that the Justice Department had interviewed witnesses, including flight crew, as part of the investigation into the Jan. 5 accident, in which part of the plane's fuselage exploded mid-flight.

Alaska Airlines said it is cooperating with authorities.

“In an event like this, it is normal for the Department of Justice to conduct an investigation. Alaska Airlines said in a statement to Al Jazeera: “We are fully cooperating and do not believe we are a target of the investigation.”

Boeing declined to comment.

The investigation comes as Boeing is under scrutiny over its safety record following a series of accidents, including two fatal crashes involving the Boeing 737 MAX in 2018 and 2019.

The Justice Department's investigation will inform authorities to evaluate whether Boeing complied with the terms of a $2.5 billion settlement to avoid prosecution in connection with the incidents, the Wall Street Journal reported.

The US Federal Aviation Administration (FAA) said on Monday it had identified “noncompliance issues in Boeing's manufacturing process monitoring, parts handling and storage, and product control” after a review of the company that included interviews with employees and a visit to its production line.

The FAA said Boeing will have 90 days to come up with a plan to correct the problems.

A separate Federal Aviation Administration report, released last month but released before the explosion, found serious problems with Boeing's safety culture, including fears of retaliation among employees with safety concerns.

Boeing said in a letter to the US Congress on Friday that it was unable to locate records of work done on a door panel that fell from an Alaska Airlines plane.

The Seattle-based aircraft manufacturer said it believes records related to the plate were never created despite company rules requiring such documentation.