WASHINGTON (Reuters) - U.S. Transportation Secretary Pete Buttigieg said Monday he expects Boeing to cooperate in investigations by the Justice Department and National Transportation Safety Board into the Alaska Airlines 737 MAX 9 mid-air emergency on Jan. 5.

"We respect the independence of DOJ and NTSB doing their own work, but we're not neutral on the question of whether Boeing should fully cooperate with any NTSB us word because they should," Buttigieg told a press conference.

He said Federal Aviation Administration (FAA) chief Michael Whitaker has made clear to Boeing that "they need to go through a serious transformation in terms of their responsiveness, their culture."

Boeing, which did not immediately comment Monday, said Friday it believes that, during production of a 737 MAX 9, required documents were never created that should have detailed the removal of a key part that failed. The company said it is "committed to continuing to cooperate fully and transparently with the NTSB's investigation."

Alaska Airlines said Saturday it is cooperating with the Justice Department in its criminal investigation:

"It's normal for the DOJ to be conducting an investigation. We are fully cooperating and do not believe we are a target of the investigation."

In the aftermath of the incident, the FAA grounded the MAX 9 for several weeks, barred Boeing from increasing the MAX production rate and ordered it to develop a comprehensive plan to address "systemic quality-control issues" within 90 days.

NTSB Chair Jennifer Homendy on Wednesday criticized what she termed Boeing's lack of cooperation and failure to disclose some documents, including on the door plug opening and closing, as well as the names of 25 workers on the door crew at the 737 factory in Renton, Washington.

"It is absurd that two months later we don't have it," Homendy said.

After Homendy's comments, Boeing provided the 25 names.

Whitaker said Monday the agency and Boeing hope to define in the next 30 days the milestones Boeing must meet.

"We're really focused on quality assurance process where there really are gaps," Whitaker said, citing issues like "having the employees have the right tools and training, having the right engineering drawings, and assembling the aircraft in the proper order."