Three Democratic U.S. senators on Tuesday introduced sweeping legislation to reform how new airplanes are certified and overseen by U.S. regulators after two fatal Boeing 737 MAX crashes killed 346 people.

FILE PHOTO: Employees walk past a Boeing 737 Max aircraft at Boeing's 737 Max production facility in Renton, Washington, U.S. December 16, 2019. REUTERS/Lindsey Wasson/File Photo