Boeing drew fresh criticism from a federal regulator on Thursday over disclosures about the continuing investigation into a harrowing January flight during which one of the company’s 737 Max planes lost a panel, exposing passengers to howling winds at an altitude of about 16,000 feet.

Addressing reporters at a company factory in Renton, Wash., Elizabeth Lund, a Boeing executive, provided new details on Tuesday about how the plane involved in the incident left the plant apparently without four critical bolts that secured the panel, known as a door plug, in place.

Boeing said the information was not for release until Thursday morning, under a common kind of agreement that allowed the attending reporters time to process the detailed briefing.

But the National Transportation Safety Board became aware of the remarks at the briefing and rebuked the company hours before articles on the remarks were published. It said that Boeing improperly shared investigative information and speculated about the cause of the incident, adding that the company had “blatantly violated” the agency’s rules surrounding active investigations. The agency said it would provide details about that violation to the Justice Department, which is investigating the January flight.

“As a party to many N.T.S.B. investigations over the past decades, few entities know the rules better than Boeing,” the agency said in a statement.

The N.T.S.B. also said that it would revoke Boeing’s access to investigative information and that the company would not be allowed to ask questions of other participants at a hearing in August, for which it plans to subpoena Boeing witnesses. The agency said it confirmed the company’s violation after obtaining a transcript of the press briefing from Boeing. The agency’s rebuke of the company was earlier reported by The Air Current, an aviation publication.

In a statement, Boeing apologized for speaking out of turn.

“We deeply regret that some of our comments, intended to make clear our responsibility in the accident and explain the actions we are taking, overstepped the N.T.S.B.’s role as the source of investigative information,” the company said. “We apologize to the N.T.S.B. and stand ready to answer any questions as the agency continues its investigation.”

In a letter addressed to Boeing’s chief executive, Dave Calhoun, an N.T.S.B. official noted that the agency had already warned Boeing in March about adhering to its rules. The official also suggested that Boeing’s chief engineer, Howard McKenzie, had gone too far during a Senate hearing last week when he said an unusual midair wobble of a Max jet operated by Southwest Airlines appeared to be unrelated to plane design or manufacturing. The agency is also investigating that incident.

“It is crucial that the investigation speaks with one voice — that of the N.T.S.B. — to prevent the release of inaccurate, misleading, unconfirmed and out-of-context investigative information to the media, public and lawmakers, which is exactly what occurred during Boeing’s media briefing,” said the official, Timothy J. LeBaron, the director of the agency’s office of aviation.

The January incident on an Alaska Airlines flight resulted in no major injuries, but it raised fresh concerns about the quality of Boeing’s planes more than five years after two fatal crashes involving the Max. In response, Boeing announced changes aimed at improving quality and safety, including expanding training, simplifying plans and procedures and reducing defects from suppliers.

Boeing held the Tuesday briefing, followed by a factory tour, to show the progress it had made so far toward improving quality. Ms. Lund also offered new details on the events that preceded the incident.

When the body of the plane involved in the January flight arrived at Boeing’s factory in the summer of 2023, five rivets did not meet specifications. As the plane worked its way through the factory, Boeing and the supplier that made the body, Spirit AeroSystems, discussed how to address the problem, Ms. Lund said in the briefing this week. By the time they decided that the rivets needed to be replaced, work on the plane was nearing completion.

The panel was removed to fix the nearby rivets, but no one documented that removal. Later, a team known as a “move crew” prepared the aircraft to be brought outside, closing the panel, she said. It was not the responsibility of that crew to replace the bolts that had secured the door and the lack of documentation meant that no one else knew to replace the bolts, Ms. Lund added.

The panel, which fit snugly into the gap it covered, survived about 500 hours in flight before blowing out on the Alaska Airlines flight.

Asked by a reporter about the individuals involved, Ms. Lund said that “the ‘who’ is absolutely in the responsibility of the N.T.S.B.” and declined to comment further. The agency took issue with that characterization, saying it was “focused on the probable cause of the accident, not placing blame on any individual or assessing liability.” That approach is crucial to such investigations because it encourages individuals with information to come forward without excessive fear of retribution.

Ms. Lund was promoted as part of a leadership shake-up in February, taking on her current role as a senior vice president overseeing quality across all of Boeing’s commercial airplanes. She was most recently in charge of commercial plane production programs. Before that, she held other executive roles, including supervising supply chain development and strategy.

The January incident was a new blow to Boeing’s reputation after two crashes of Max 8 planes in 2018 and 2019, in which 346 people died. The crashes led to a global ban on the Max that lasted about 20 months; the plane started flying again in late 2020.

For years after the crashes, Boeing’s executives assured regulators, airlines and the public that they had made sweeping changes to improve the quality and safety of its planes. But the January incident — and accounts from current and former employees about shoddy work and poor management decisions, as reported by The New York Times and others — suggested that the changes it had made then had not gone far enough.

One of the more important changes Boeing has made since January was requiring that bodies of 737 Max planes pass a more rigorous inspection before being shipped to Renton, near Seattle, for final assembly. The body is made in Wichita, Kan., by Spirit, a supplier that Boeing is expected to soon acquire.

That change took effect a few months ago and has resulted in significantly fewer major defects that need to be fixed at Boeing’s factory, said Ms. Lund. The supplier inspections have also allowed Boeing to make the Max more quickly once the bodies arrive at its factory.

The company is also producing fewer planes than planned because the Federal Aviation Administration, its main regulator, limited its production rate after the January flight.

“We’ve strengthened our presence at the supplier, we ensure the parts are perfect where they ship, we inspect them there, they rework them there, and then we ship the parts,” Ms. Lund said. “The benefits have been really tremendous.”

Ms. Lund said that the earlier Max crisis had forced Boeing to reform its engineering practices, but that the more recent incident had required improvements to the production process.

“When this accident came along, it gave us a chance to look at a different area,” she said.

Other improvements the company has made, Ms. Lund said, include more training for new hires before they start working on planes and expanded on-the-job training. The company dispatched more than 160 workplace coaches, including veteran and retired mechanics, to help newer workers get up to speed.

The company is also accelerating efforts to simplify an array of plans and procedures, Ms. Lund said. Boeing has increased inspections and internal monitoring and placed renewed emphasis on encouraging workers to speak up about concerns, collecting thousands of new comments and recommendations on improving quality.

Boeing has also been trying to reduce work performed out of sequence, known as traveled work, which can increase the risk of mistakes and cause other problems. The company said it had imposed more stringent requirements that had to be met before planes could advance down the production line. That and other changes have helped the company cut the amount of traveled work back by more than 50 percent, Ms. Lund said.