Boeing Co said on Sunday it understood the outcry over leaked messages from a former test pilot over erratic software behavior on its 737 MAX jet two years before recent crashes and added it was still investigating what they meant.

The world's largest planemaker, under growing pressure to explain what it knew about 737 MAX problems before it entered service, said it had not been able to speak directly to former employee Mark Forkner but echoed his lawyer's subsequent claims that the problems were linked to a faulty simulator.

The role of the simulator has emerged as a crucial issue since the 2016 messages surfaced on Friday, since investigators will want to know whether erratic movements reported by the pilot meant Boeing was aware of problems on the aircraft itself or only in the artificial cockpit.

The FAA on Friday ordered Boeing Chief Executive Dennis Muilenburg to give an "immediate" explanation for the delay in turning over the "concerning" document, which Boeing discovered some months ago.

In the messages from November 2016, then-chief technical pilot Forkner tells a colleague the so-called MCAS anti-stall system - the same one linked to deadly crashes in Indonesia and Ethiopia - was "running rampant" in a flight simulator session.

At another point he says: "I basically lied to the regulators (unknowingly)."

The messages, first reported by Reuters, prompted a new call in Congress for Boeing to shake up its management as it scrambles to rebuild trust and lift an eight-month safety ban of its fastest-selling plane.

"We understand entirely the scrutiny this matter is receiving, and are committed to working with investigative authorities and the U.S. Congress as they continue their investigations," Boeing said in its statement on Sunday.

Boeing said it informed the FAA about its decision to expand MCAS to low speeds. The FAA also observed MCAS operation in the low-speed configuration during certification flight testing, from August 2016 through January 2017, Boeing said.

The instant messages prompted harsh reactions from several Democratic lawmakers in Washington, with Representative Peter DeFazio saying, "This is no isolated incident."

"The outrageous instant message chain between two Boeing employees" suggests "Boeing withheld damning information from the FAA," DeFazio, who chairs the U.S. House Transportation Committee, said on Friday.

Muilenburg, who was stripped of his chairman title by the company's board nine days ago, is set to testify before the committee on Oct. 30.

'UNDUE PRESSURE'

DeFazio's committee also obtained details of a 2016 Boeing survey that found nearly 40% of 523 employees handling safety certification work perceived "potential undue pressure" from managers, such as bullying or coercion.

Other top concerns include "schedule pressure" and "high workload," though 90% of the employees said they were comfortable raising concerns about "undue pressure" to management, according to a copy of the Boeing presentation of the survey results seen by Reuters on Sunday.

The presentation was obtained by the committee's investigators and not among a trove of documents handed over the committee by Boeing itself, a person briefed on the matter said.

Evidence of "undue pressure" was also pinpointed by a group of international regulators reviewing the 737 MAX certification.

A Boeing spokesman did not immediately respond to a request for comment on the survey results.

SIMULATOR FLAWS

On Sunday, Boeing said it has not been able to speak to Forkner directly about his understanding of the document.

"He has stated through his attorney that his comments reflected a reaction to a simulator program that was not functioning properly and that was still undergoing testing," Boeing said.

"The simulator software used during the Nov. 15 session was still undergoing testing and qualification and had not been finalized," Boeing added.

Reuters reported on Friday that the simulator had a number of software problems, citing a former Boeing test pilot who analyzed the transcript and who had direct knowledge of the flight simulator at the time.

Such calibration problems may have contributed in some way to Forkner's observations and conclusions about MCAS' behavior, the former pilot, and a second former Boeing engineering employee, Rick Ludtke, said.

Boeing's statement was released as its board of directors and top executives from its airplanes division and supply chain gathered in San Antonio, Texas for previously scheduled meetings on Sunday and Monday.

The board meetings come as pressure mounts on the Chicago-based company not only from the regulatory and criminal investigations stemming from the crashes but also from the financial burden caused by the jet's safety ban and continued high production.

Several industry sources said there was speculation inside the company of significant job cuts as it continues to experience a cash drain. The 737 production rate may also have to come down if regulators further delay the MAX's return to service, the people said.