The FBI is reportedly joining the government's investigation into Boeing's 737 Max plane

Federal investigators are looking into how Boeing's 737 Max plane was certified to fly. The FBI is also joining the Department of Transportation's inquiry, the Seattle Times reported. The FBI is joining the Department of Transportation's investigation into the Boeing 737 Max plane, the Seattle Times reported Wednesday.People familiar with the matter told reporter Steve Miletich that the investigation is focused on how the plane, which has crashed twice in the past five months, was certified to fly. Department of Transportation Secretary Elaine Chao formally requested an audit of the FAA's certification for the process in a letter sent to the agency on Tuesday.The FBI did not immediately respond to a request for comment.Separately, the Pentagon's inspector general said Wednesday that it will investigate a watchdog group's allegations that acting Defense Secretary Patrick Shanahan has used his office to promote his former employer, Boeing.Read the full Seattle Times report here.More on the investigations into Boeing and its 737 Max plane:Everything we know about Ethiopian Airlines deadly crash of a Boeing 737 Max 8, the second disaster involving the plane in 5 months, and what Boeing is doing to ensure it never happens againThe crashed Lion Air 737 Max had the same malfunction the day before, but crew figured out how to stop it. The information never made it to the next flightBoeing reshuffles its top engineers amid 737 Max crisisA cockpit voice recording from doomed Lion Air 737 Max shows pilots scoured the plane's manual to fix its fatal dive but couldn't find the right procedure in timeThe Boeing 737 Max is likely to be the last version of the best-selling airliner of all timeThe US government wants to audit how the Boeing 737 Max got approved to fly by the FAA