Boeing 737
© Reuters/Lindsey Wasson
737 MAX aircraft at Boeing facilities at the Grant County International Airport in Moses Lake, Washington, September 16, 2019.
Text messages between two Boeing employees implying they "lied to the regulators" about problems with the safety software of 737 MAX passenger jets have been reportedly given to investigators, as the planes remain out of service. The exchanges from 2016 between MAX chief technical pilot Mark Forkner and another unnamed pilot at Boeing are now with the Federal Aviation Administration, according to documents seen by Reuters.

The FAA is said to have found the information "concerning" and is reviewing it "to determine what action is appropriate." FAA Administrator Steve Dickson also wrote to Boeing CEO Dennis Muilenburg demanding an "immediate" explanation for why the texts had not been turned over sooner.

"I basically lied to the regulators (unknowingly)," Forkner reportedly says in one of the messages, referring to an issue with the MCAS software intended to keep the jet stable. The other employee responded with "it wasn't a lie, no one told us that was the case." "Granted I suck at flying, but even this was egregious," Forkner replied.

He has left the company since. The Seattle Times reported last month that he repeatedly invoked his Fifth Amendment rights against self-incrimination to avoid turning over documents subpoenaed by the Department of Justice.

The MCAS anti-stall system has been blamed for causing the crashes of Lion Air and Ethiopian Airlines 737 MAX jets, which claimed 346 lives. All 737 MAX planes were grounded after the Ethiopian Airlines crash in March, and remain out of service the world over, pending investigations by US regulators.

Boeing shares slipped almost four percent following the news about the text messages. The company said it is revising the MCAS software to include additional safeguards, and reportedly intends to turn over additional texts to Congress on Friday.

The 737 MAX was Boeing's most popular narrow-body passenger jet, used by major US airlines and around the world. With new, bigger engines added to the body originally designed in the 1960s, it required complex software controls to keep the plane balanced.

Multiple revelations about software problems and procedural flaws over the past six months have raised doubts that the planes would ever come back into service, as both passengers and pilots appear to have lost all confidence in the model.