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AFP
Boeing employees exchanged instant messages about issues with the automated safety system on the 737 Max as it was being certified in 2016.
In documents provided by Boeing to lawmakers, a pilot wrote that he had run into unexpected trouble during tests.
He said he had “basically lied to the regulators [unknowingly]”.
The safety system has been tied to two deadly crashes that killed 346 people.
The Federal Aviation Administration (FAA) called the document “concerning” and said it was asking Boeing for an “immediate” explanation for the delay in turning over the documents, which Boeing provided to lawmakers ahead of hearings this month.
Boeing boss Dennis Muilenburg is due to testify. He was recently stripped of the title of chairman of the company, though he remains chief executive.
Boeing said it is cooperating with the investigation of the 737 Max, which has been grounded globally since March following the crashes.
“We will continue to follow the direction of the FAA and other global regulators, as we work to safely return the 737 MAX to service,” Boeing said.
Reviews since the crashes have found fault with Boeing and the Federal Aviation Administration (FAA), which regulates flight safety, for inadequate review of the risks associated with a new anti-stall software control system known as Mcas.
Boeing reportedly uncovered the messages, which date to 2016, “some months ago”. The pilot no longer works for the company.
In response to the pilot’s message, the other Boeing employee wrote: “It wasn’t (sic) a lie, no one told us that was the case”.
Shares in the company dropped more than 5% on Friday following the reports.