Watch Boeing CEO Dennis Muilenburg testify before the House on 737 Max crashes

Boeing CEO Dennis Muilenburg is back on Capitol Hill on Wednesday for a second congressional hearing at 10 a.m. ET about two deadly crashes of the 737 Max.

Senators criticized Boeing and Muilenburg in a hearing on Tuesday — the beleaguered CEO's first public appearance in Congress since the crashes — and questioned whether greater federal oversight of commercial aircraft development is necessary. Muilenburg apologized and admitted to the Senate panel that the company's safety assumptions and testing of the plane fell short, but he said that the company followed existing rules.

At one tense moment in the hearing, Sen. Richard Blumenthal, D-Conn., equated the 737 Max to "flying coffins."

Lawmakers on Tuesday are likely to press Muilenburg again on whether the Federal Aviation Administration handed over too much control to Boeing in certifying the jets as safe. The planes are Boeing's best-selling aircraft but the two Max crashes — a Lion Air flight that went down in October 2018 shortly after takeoff from Jakarta and an Ethiopian Airlines plane that crashed at a similar stage in flight in Ethiopia in March — prompted a worldwide grounding.

"Our investigation and this hearing are not just about getting answers to our questions, but about making the aviation system safer, for all who travel, and ensuring tragedies like those in Indonesia and Ethiopia never happen again," said Rep. Peter DeFazio, D-Ore., chair of the House Committee on Transportation and Infrastructure that's holding Wednesday's hearing, said in written testimony.

A key issue is how Boeing marketed the 737 Max to customers around the world, promising minimal training for pilots to transition from older models of the 737, which Boeing first introduced in 1967.

DeFazio's written testimony said Boeing offered Southwest Airlines, its biggest U.S. Max customer, a rebate of $1 million per plane, which has a list price of more than $120 million, if pilots needed simulator training. Before the 737 Max debuted, airline pilots received computer-based training to transition from older models of the plane.

Boeing president and CEO, Dennis Muilenburg(C) arrives for a full committee hearing on "Aviation Safety and the Future of Boeing's 737 MAX." on Capitol Hill October 29, 2019 in Washington,DC.
Mandel Ngan | AFP | Getty Images