The acting head of the Federal Aviation Administration told lawmakers Wednesday that Boeing should have given pilots more information about a new anti-stall system that is suspected in two deadly crashes of the 737 Max since October.
"I, as a pilot, when I first heard about this, I thought there should have been more text in the manual" about the MCAS anti-stall system Boeing added to the planes before they were delivered to customers, Daniel Elwell, the FAA's acting administrator, told a House aviation subcommittee.
The fast-selling 737 Max has been grounded worldwide after the second crash, in Ethiopia in March. The first crash, in October, happened in Indonesia. The two accidents killed 346 people.
Investigators have pointed to erroneous sensor data that fed into the planes' new, automated anti-stall system in the crashes shortly after takeoff in both deadly flights. Some pilots complained that they weren't aware the MCAS system existed on the planes until after the crash of the Lion Air flight in Indonesia.
Audio surfaced this week of a tense meeting in November in which airline pilots confronted a Boeing executive after the Lion Air crash, angry that they weren't informed about automated system. Boeing vice president Mike Sinnett told the pilots: "I don't know that understanding this system would've changed the outcome on this. In a million miles, you're going to maybe fly this airplane, maybe once you're going to see this, ever," according to audio reviewed by CNBC.
The FAA is facing several investigations about its role in approving the new planes in 2017 as well as heightened scrutiny of its practice of using company employees to help certify the aircraft before the planes are delivered to airlines.
Elwell also said Boeing engineers discovered a problem with displays that show if sensors on the plane were giving bad information, but the FAA didn't find out about it for more than a year. The sensors in question transmit what is known as the angle of attack — the angle of the aircraft relative to oncoming air.
"I am not happy with 13-month gap" between the discovery by Boeing and when the FAA and customers found out, Elwell said. He added that the displays are not critical to flight safety and that the agency welcomes scrutiny and has room to improve.
Boeing in a statement said the company appreciates Elwell's comments "as well as those of other pilots, airline customers and global regulators that have expressed concerns.
"We will continue to listen and to take the steps necessary to enhance safety," said Boeing's statement.
Some lawmakers criticized the FAA for its oversight and questioned its longtime practice of using manufacturers own employees to help speed aircraft certification.
"The FAA needs to fix its credibility problem," Rep. Rick Larsen, D-Wash., and chairman of the subcommittee on aviation, said in prepared remarks.
Rep. Peter DeFazio, D-Ore., said "Boeing is yet to provide a single document" to the House panel about the plane.
Boeing is working on a fix for the planes that would give pilots more control over the system and use data from two, instead of one sensor, but the grounding has already pinched some airlines' revenue and is threatening to crimp sales further if the planes remain off limits during the peak summer travel season.
"If the public doesn't feel safe about flying then they won't fly," Larsen said.
Elwell said the FAA will allow the planes to fly again once it's "absolutely safe to do so. ... It's important we get this right."
Also Wednesday, the Senate Committee on Commerce, Science and Transportation held nomination hearing for President Donald Trump's pick to run the FAA, former Delta Air Lines executive Stephen Dickson.
CNBC's Emma Newburger contributed to this report.