US safety investigators began a two-day hearing to learn more about what caused an almost-new Boeing Co. 737 Max 9 aircraft to lose a large fuselage panel during flight at the start of the year.

The National Transportation Safety Board released thousands of pages of information on the Jan. 5 accident involving the jet flown by Alaska Airlines. Interviews with flight crew paint a picture of a frenzied scene after the fuselage panel — known as a door plug — blew off while the plane was still ascending. That prompted the cabin to lose pressure and the cockpit door to swing open.

“It was chaos,” the flight’s first officer told safety investigators, according to a transcript. The first officer said she could see cabin tubes hanging from the ceiling through the open door, “and at that point my focus was forward, and I yelled get down, get down.” 

While nobody was seriously hurt in the accident, the episode has plunged Boeing into crisis, prompting a management shakeup and comprehensive review of the company’s safety culture. Elizabeth Lund, a Boeing senior vice president of quality testifying at the hearing, said the planemaker is only now starting to improve its rate of aircraft production again, which she said had fallen precipitously after the accident. 

Boeing has sought to show how the company has learned from the episode, as it tries to dig itself out of the crisis that has drained billions of dollars from its balance sheet and has weighed on the stock price. NTSB Chair Jennifer Homendy, for her part, has taken a tough line, with interactions between officials and the company boiling over at times in the past few months. 

“This isn’t a PR campaign for Boeing,” Homendy said at the hearing, after a Boeing executive touted the improvements the company has made following the accident. “What is very confusing for a lot of people who are watching, who are listening, is what was going on then. This is an investigation on what happened on Jan. 5.” 

Boeing is still striving to emerge from crisis mode. The company announced a new chief executive officer last week, it has agreed to buy back supplier Spirit AeroSystems Inc. to gain greater control of its manufacturing, and the company pleaded guilty to a single conspiracy charge by US prosecutors stemming from two previous 737 Max crashes. 

Its stock has lost more than a third of its value this year, and the company burned through more than $1 billion in cash each month as it slowed output. 

From the beginning, the door-plug mishap was a unique case. While nobody was seriously injured, the accident attracted huge public interest. The panel was found in a yard shortly afterward, and investigators quickly identified it had been missing four bolts to keep it in place. In a twist, an anonymous tipster published a lengthy online account, documenting the breakdowns that led to the jet leaving the factory without the bolts.

A preliminary report released by the NTSB corroborated parts of that account. It found evidence suggesting the door plug was removed prior to leaving the facility to fix damaged rivets and then reinstalled without being properly attached. Boeing has said it’s missing formal documentation on the panel’s removal, a serious violation of its manufacturing protocols. 

The jet’s fuselage arrived from Spirit with defective rivets on the mid-exit door, Lund said during a reporter briefing in June. As it wound through the factory, Boeing and Spirit representatives in the Renton, Washington, factory debated what should be done and who was responsible.

The jet was at the end of the line before the companies agreed on a plan that would require removing the door plug for the repair. But while the rivet work was entered into Boeing’s formal record system, there was no mention of the door removal. Workers who put it back thought they were doing so temporarily while the aircraft was parked outside to protect it from the elements. 

In the absence of documentation, the team that prepared the plane for delivery was unaware the bolts were missing, and quality inspectors wouldn’t have known to check the workmanship, Lund said at the time.

Since the accident, the planemaker has overhauled its management team and slowed work to a crawl in its factories as it retrained mechanics and managers, while also encouraging workers to flag quality breakdowns. It stepped up inspections, including at Spirit, in an effort to tackle defects and missing parts that lead to so-called “traveled work” where tasks are completed out of the normal sequence. 

Lund said at the hearing that Boeing engineers are working on design changes that would prevent the door plug from being closed until it’s firmly secured. She said she expects those could be implemented within the year and then will be made available for retrofit in the fleet once the design is certified.