DALLAS (BLOOMBERG) - Boeing said another high-ranking executive working on the company's response to the 737 Max crisis will step down.

Michael Luttig, 65, will retire at year-end, Boeing said in a statement on Thursday (Dec 26), three days after the planemaker announced the departure of Dennis Muilenburg as chief executive officer.

Luttig, the company's former general counsel, was reassigned in May to advise Muilenburg and the board of directors on legal matters related to two deadly Max crashes.

Luttig's departure adds to the management turmoil at Boeing as the nine-month grounding of the manufacturer's best-selling jet drags on.

David Calhoun, a board member who took over as chairman in October, will replace Muilenburg on Jan 13.

Chief Financial Officer Greg Smith is serving as interim CEO.

Boeing is under increased pressure in Washington after disclosing a new batch of internal communications about the Max's development to the US Federal Aviation Administration on Dec 23. That was the same day Muilenburg stepped down.

The messages between Boeing employees paint a "very disturbing picture", according to an aide to a House of Representatives committee. At least some of the messages were written by the same Boeing pilot whose 2016 communications became the subject of sharp questioning by lawmakers in October, Bloomberg News reported earlier this week.

The documents have not been released publicly.

The staff of the Transportation and Infrastructure Committee are still reviewing the messages and did not provide detailed descriptions of what they contain.

"Similar to other records previously disclosed by Boeing, the records appear to point to a very disturbing picture of both concerns expressed by Boeing employees about the company's commitment to safety and efforts by some employees to ensure Boeing's production plans were not diverted by regulators or others," a committee aide said in a statement.

Boeing said earlier this week that "the tone and content of some of these communications do not reflect the company we are and need to be".

Luttig had served as a judge in federal appeals court before joining Chicago-based Boeing in 2006. Executives at the company have typically retired at 65.