The US Justice Department has issued summons as part of an investigation into certification and marketing of Boeing 737 Max 8 planes, the CNN reported on Thursday.
Prosecutors wrote to Boeing a day after Transportation Secretary Elaine Chao asked the agency to look into the aircraft’s certification.
Ms Chao on Tuesday sent a memo to Calvin Scovel, the department’s inspector general, formalising the request.
“Safety is the top priority of the Department, and all of us are saddened by the fatalities resulting from the recent accidents involving two Boeing 737-Max 8 aircraft in Indonesia and Ethiopia,” Ms Chao wrote.
Boeing requested an amended type certification for 737-Max 8 aircraft in January 2012, and the Federal Aviation Administration issued the certification in March 2017.
“To help inform the Department’s decision making and the public’s understanding, and to assist the FAA in ensuring that its safety procedures are implemented effectively, this is to confirm my request that the Office of Inspector-General proceed with an audit to compile an objective and detailed factual history of the activities that resulted in the certification of the Boeing 737-Max 8 aircraft.”
The plane maker is required to provide information on safety and certification procedures— including training manuals for pilots.
The investigation in the wake of Ethiopia Airlines Flight 302 crash that claimed the lives of all 157 aboard but CNN reports that the scrutiny began after the October 2018 Lion Air disaster in Indonesia.
The investigations come days after Ethiopia's Transport Minister Dagmawit Moges said black box data recovered from an Ethiopian Airlines plane show "clear similarities" with the craft that plummeted in Indonesia.
He said the parallels would be the "subject of further study during the investigation," with a preliminary report issued in "30 days".
The Ethiopian Airlines flight 302 came down into a field southeast of Addis Ababa minutes into its flight to Nairobi.
The disaster caused the worldwide grounding of the Boeing 737 MAX 8 aircraft after aviation regulators noticed similarities with the Indonesian disaster that killed all 189 onboard.
Both planes reportedly experienced erratic steep climbs and descents as well as fluctuating airspeeds before tumbling down shortly after take-off.
Questions have been raised on an automated anti-stalling system introduced on the 737 MAX 8, designed to automatically point the nose of the plane downward if it is in danger of stalling.