Boeing's 737 Max 8 planes have been grounded worldwide in the wake of two fatal crashes that resulted in the deaths of 346 people.
According to a 2016 transcript of messages sent between former 737 Max 8 chief technical pilot Mark Forkner and another Boeing employee, the Maneuvering Characteristics Augmentation System (MCAS) was behaving erratically and "running rampant" in simulations.
The MCAS system is designed to automatically adjust the plane's "angle of attack" when it detects the plane is stalling.
Eight months later, Forkner requested that the Federal Aviation Administration (FAA) remove mention of the MCAS from the pilot's manual.
The FAA was placed under the impression that the system could only be turned on in rare instances, and therefore approved the request.
The system has since been linked to both the Lion Air Flight 610 crash in October 2018 and the Ethiopian Airlines Flight 302 crash in March this year.
Boeing in trouble
The transcript were recently turned over to the US Department of Transport, although Boeing reportedly discovered this information months ago.
The FAA has demanded an immediate explanation from Boeing CEO Dennis Muilenburg about the delay, while the US Congress called for Boeing to sort out its management issues.
Muilenburg, who recently lost his position as Boeing chairman, is also due to testify before the House Committee on Transportation and Infrastructure on 30 October.
Boeing said the grounding of the 737 Max has already cost the company at least $8 billion.
