WASHINGTON — The United States will not clear Boeing 737 Max jets for flight again until federal officials are satisfied that Boeing has fixed its flawed flight control system, Transportation Secretary Elaine L. Chao said in testimony on Wednesday.
Ms. Chao, appearing before House subcommittee hearings concerning her department’s budget, offered no timeline for the plane to return to service after the Federal Aviation Administration’s decision to ground the jets on March 13.
But she said Boeing appeared close to completing a software upgrade on a crucial sensor believed to have played a role in the crashes of two Max jets. An Ethiopian Airlines flight crashed shortly after takeoff from Addis Ababa on March 10, killing 157, and a Lion Air 737 Max crashed last October, killing all 189 people on board.
“The F.A.A. will not approve Boeing’s proposed changes until the F.A.A. is satisfied it is safe,” said Ms. Chao, who has come under fire for her department’s actions after the Lion Air disaster.
Ms. Chao, reading from prepared answers at times, defended the F.A.A.’s decision not to follow the lead of 40 other countries by immediately grounding the fleet, despite the possibility that the Ethiopia crash might have resulted from a flaw in a plane whose basic design dates to the 1960s.
The F.A.A., which Ms. Chao oversees, waited three days to ground the fleet and was one of the last major regulators worldwide to do so. She flew back to Washington from a festival in Texas on March 12 on a 737 Max, in what seemed to be an endorsement of the plane’s safety. Less than a day later the F.A.A. uncovered evidence that suggested the planes were not fit to fly.
“The F.A.A. saw no basis upon which to ground these planes,” she said. “It is a very technical organization. It is very data-driven. They saw no data until the morning of Wednesday the 13th.”
It was at that time, she added, that F.A.A. investigators discovered “new information on the first three minutes of the Ethiopian” flight that revealed “parallel conditions” involving the two accidents.
But in an interview after the hearing, Ms. Chao made it clear that the decision to ground the jets was the F.A.A.’s — not her own — and said that she had no legal say, then or now, in deciding when the planes fly.
F.A.A. officials “are very careful about jumping to conclusions, having gone through other tragedies,” she said. “They are very careful about rushing to action.”
Ms. Chao’s critics have argued that she could have exerted greater pressure on F.A.A. officials and avoided the appearance that she was endorsing the aircraft’s airworthiness.
When asked, after the hearing, about her 737 flight from Texas, Mr. Chao said: “I flew down on the 737 and I flew back on the 737. Those are the flights that were chosen, so I went on it. I didn’t really have any concern about the safety, but that is irrelevant now.”
At the hearing, Representative David Price, Democrat of North Carolina and the chairman of the House Appropriations transportation subcommittee, asked a pointed question: “Were there any lessons learned?” He added, “Should or could the F.A.A. have taken a different approach?”
Mr. Price also pressed Ms. Chao on whether the review process for new aircraft designs gives Boeing and other manufacturers too much latitude in overseeing their own designs and upgrades, a process critics have likened to self-certification.
Ms. Chao said she did not yet “have answers” but said she had taken two steps — prompting an inquiry into the crashes by the department’s inspector general and convening a special panel to look into the issue.
“We always need to improve,” she said.