Lawmakers grill FAA chief over Boeing 737 MAX 8 safety questions

Lawmakers on Wednesday grilled the head of the Federal Aviation Administration over how his agency handled the safety certification of the Boeing 737 MAX 8 involved in two crashes that left 346 people dead.

Acting Administrator Daniel Elwell faced questions from members of the House Transportation Committee about the FAA's role in approving the now grounded plane.

"The FAA has a credibility problem," said House Transportation subcommittee chairman Rep. Rick Larsen, D-Wa. "The FAA must take steps to restore the public's confidence."

"In the U.S., the 737 MAX will return to service only when the FAA's analysis of the facts and technical data indicate that it is safe to do so," Elwell said in his opening remarks. .

Wednesday's hearing marked the first in a series of investigations into why regulators or Boeing did not require pilots to go through training for the scrutinized automated safety system suspected in playing a critical role in the two crashes and why that system wasn't detailed in the plane's flight manual prior to the Lion Air crash in Indonesia last fall. An Ethiopian Airlines 737 MAX 8 crashed in March.

The MCAS, or Maneuvering Characteristics Augmentation System, is designed to prevent an aircraft from going into a stall by pitching the nose of the aircraft down. The 737 MAX 8 has two angle-of-attack sensors sensors but only receives data from one. If that one sensor malfunctions and feeds incorrect data, the MCAS function fires off and will pitch the nose down.

"How can we have a single point of failure in a modern aircraft?" Rep. Peter DeFazio, D-Ore., asked in his opening statement.

Later, DeFazio asked Elwell if it's correct that, prior to the Lion Air crash, the pilots didn't know the MCAS system was installed.

Elwell acknowledged, "That's correct."

DeFazio also asked Elwell if he thought that the MCAS functions should have been more adequately explained to pilots.

"As a pilot, when I first heard about this, I thought that there should have been more text in the manual about the MCAS," Elwell responded.

The certification of this aircraft has been the subject of intense scrutiny and speculation, and the Wall Street Journal report recently reported that "senior agency officials didn't participate in or monitor crucial safety assessments of a flight-control system" for the 737 MAX 8 jet.

While Elwell did not say how closely FAA officials worked with Boeing engineers and test pilots in the certification of MCAS, he did said that it took a total of five years to certify the 737 MAX 8.

"The process included 297 certification flight tests, some of which encompassed tests of the MCAS functions," Elwell said.

DeFazio pointed out that parents of 24-year-old Samya Stumo - killed in the Ethiopia Airlines crash were in the audience.

"Their daughter was flying from Ethiopia to Kenya for work when Ethiopian Airlines Flight 302 went down," DeFazio said. "They deserve answers and accountability, as does the general flying public."

ABC News' Christine Theodorou contributed to this report.