The head of a U.S. Senate panel reviewing two catastrophic Boeing 737 Max crashes told Reuters ahead of hearings this week that the plane would not return to U.S. skies until "99.9 percent of the American public" and policymakers are convinced it is safe.

Boeing Co. Chief Executive Dennis Muilenburg will testify for two days before Congress starting on Tuesday, which is the anniversary of the Lion Air 737 Max crash in Indonesia, the first of two crashes within five months that killed a total of 346 people.

"Clearly the accidents didn't have to happen and I don't think there was sufficient attention to how different pilots would react to signals in the cockpit," Sen. Roger Wicker, a Republican who chairs the Senate Commerce Committee that will hold the first hearing, said in an interview on Friday.