Newly-surfaced documents suggest Boeing may not be able to return its historically best seller 737 Max to service on Monday.

Boeing shares continue to slide after the US Federal Aviation Administration (FAA) criticised the American manufacturer for withholding key documents related to the two crashes that killed 346 people.

The company is now downgraded and it is feared it may soon halt the production of the jet. The market expects that if the 737 MAX’s recertification is delayed, Boeing would pay more compensation to airlines and its cash flow will fall deeper into the red.

The new damning information for Boeing is the release of instant messages between Boeing’s chief technical pilot for the 737, Mark Forkner, and management over the performance of the Maneuvering Characteristics Augmentation System (MCAS) dated back to November 2016. In these messages, Forkney expresses concerns that he did not disclose the full truth about the system’s performance to the regulators, effectively lying. The MCAS system is believed to be at the centre of two MAX crashes.

Forkner’s lawyer, David Gerger, says the problem with the MCAS was signalled by the simulator but he thought that the real plane was safe.

At the same time, The Wall Street Journal reported last weekend that a November 2016 survey of Being employees revealed than one in three felt there was under pressure regarding safety-related approvals by federal regulators.

Even before the revelations, the European Aviation Safety Agency chief, Patrick Ky, met with FAA officials last week to warn them that European approval of the 737 Max redeployment will follow that of the FAA. The FAA has made clear that it follows a thorough process rather than “a prescribed timeline” for the returning of Boeing 737 MAX to service.

Boeing completed a software of the MCAS system in September and a final round of simulator tests was expected to take place in November, potentially clearing the way for recertification in December and redeployment in January. That schedule does not now look credible. Boeing has responded to the crisis by firing chief executive Dennis Muilenburg but if the return of 737 to service is called into question, the company will need more support to stay afloat.