Boeing chief executive Dennis Muilenburg has taken to social media to call the Paris Air Show a “defining moment” for his company.

“We know we have disappointed our customers recently,” Muilenberg said on Twitter, “Many of them impacted by the Max grounding, especially as we approach the summer peak season, and we regret that impact to our customers.”

Paris is one of the world’s largest aviation showcases, when both Airbus and Boeing strive to make waves by announcing new aircraft orders, revealing new aircraft types, and groundbreaking innovations. Knowing its back was up against the wall, Boeing revealed a letter of intent from British Airways parent company IAG for 200 737 Max aircraft.

The deal would be worth $24 billion (U.S.) at list prices, though IAG negotiated a “substantial discount,” and there is no obligation to proceed with a purchase.

Boeing has been in crisis since mid-March, when the Max was grounded around the world. Canada and the United States were the last jurisdictions to ground the plane after the second crash of a Max aircraft in less than five months. In Canada, 41 aircraft with Westjet, Air Canada and Sunwing are affected by the crisis, with more waiting to be delivered. They have responded by shifting capacity, postponing unnecessary maintenance, and filling their planes to capacity.

Investigators are examining the role that a computer system meant to prevent aerodynamic stalls in certain flight conditions, called MCAS, played in the crashes.

Thankful for the opportunity to answer questions and share progress on the 737 MAX with our customers, suppliers and industry partners at the Paris Air Show. pic.twitter.com/2coR7weixH

— Dennis A. Muilenburg (@BoeingCEO) June 19, 2019

Muilenburg made the comments as a Congressional Subcommittee on Aviation resumed hearings into the certification of the Max in Washington.

Chesley Sullenberger, a pilot who survived – along with all his passengers and crew – ditching his Airbus A320 on the Hudson River in New York City in 2009, testified about the terror and confusion the Max pilots must have felt as their plane bucked and pitched before finally crashing.

“I can tell you first-hand that the startle factor is real, and huge,” Sullenberger told the committee. “Within seconds these people would have been fighting for their lives, in the fight of their lives.”

“We shouldn’t have to get pilots to compensate for a flawed design,” he said, criticizing Boeing for adding a new engines and a new MCAS computer system to the 50-year-old 737 design, without building and certifying it to the high standards expected of aircraft engineering.

“I’m here to tell you Boeing designs and engineers superb aircraft,” Captain Dan Carey, representing the Allied Pilots Association, told the subcommittee. But with the Max, Boeing let the flying public down “in a fatal and tragic way.”

He raised concerns, however, about the adequacy of the training given to pilots as the last line of defence before a tragedy.

“Is the FAA sufficiently independent of the manufacturers?” he asked the committee. Noting that the original 737 certification dates from 1967, Carey wondered if designs should have an expiration date.

“Assumptions were made by Boeing,” said former FAA Administrator Randy Babbitt, “and accepted by the FAA. The design changes should have been more rigorously tested, flight crews better educated and trained in reaction to a new safety protection system that Boeing had introduced.”

Babbitt listed a litany of planes that went on to long flying histories after initial design problems were exposed and fixed. “This has been part of aviation history,” he said.

“Safety is our top priority,” said Sharon Pinkerton, President Airlines for America, which represents several major airlines in the United States. “We don’t rely on our perfect record from the past. We know we have to get better, and we’re doing that.”

“We know we have to earn and re-earn the public’s trust,” said Muilenburg, stressing Boeing would work on its communication and transparency.

It is important to note, however, that pilots testifying before the Aviation Subcommittee complained Boeing hid vital information from them about the existence of MCAS, undermining pilots’ role as the last line of defence against a crash.