Boeing believes an interchange between two pilots about aggressive MCAS software related to an incomplete simulator program and says it briefed regulators about the now controversial 737 MAX flight control changes "on multiple occasions". The release of messages between the pilots sent the company’s share price tumbling on Friday after the US Federal Aviation Administration demanded an urgent explanation about why it was only now seeing the exchange. Boeing said in a statement released Sunday that it understood and regretted the concern the release of the messages by technical pilot Mark Forkner had caused, particularly to the FAA and other regulators. In the exchange, Forkner says the MCAS " is running rampant in the sim" and worries about unintentionally misleading regulators. Forner, who has since left Boeing, was involved in the development of training and manuals for the MAX. READ: Pilot MCAS messages plunge Boeing into fresh crisis The release comes at a delicate time for the manufacturer as it continues to deal with the regulators on getting the grounded MAX fleet back in the air. “It is unfortunate that this document, which was provided early this year to government investigators, could not be released in a manner that would have allowed for meaningful explanation,’’ Boeing said. “While we have not been able to speak to Mr. 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. “We are continuing to investigate the circumstances of this exchange, and are committed to identifying all the available facts relating to it, and to sharing those facts with the appropriate investigating and regulatory authorities. “ Boeing said it engaged in an extensive process with the FAA to determine pilot training requirements for the 737 MAX 8, part of “a complex, multiyear effort that involved a large number of individuals at both Boeing and the FAA”. “In that regulatory process, Boeing informed the FAA about the expansion of the Maneuvering Characteristics Augmentation System (MCAS) to low speeds, including by briefing the FAA and international regulators on multiple occasions about MCAS’s final configuration,’’ it said. “The process also included evaluation of MCAS in low-speed configurations for both training and certification. “The simulator software used during the November 15 session was still undergoing testing and qualification and had not been finalized, but it, too, provided for MCAS operation at low speed. “Separately, a low-speed version of MCAS was installed on the airplanes used for training-related flight testing that the FAA administered in August 2016. “And FAA personnel also observed the operation of MCAS in its low-speed configuration during certification flight testing, beginning in August 2016 and continuing through January 2017. “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. “