Text messages between Boeing employees in 2016 indicate that the company was aware of major problems with an automated feature on the 737 Max jet that made the aircraft difficult to control, the messages show.
Safety investigators say the system, known as MCAS, had repeatedly pushed the noses of planes down in Indonesia and Ethiopia, contributing to crashes that killed 346 people in the past year.
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One text message with a misspelling said the feature was engaging "itself like craxy." Another termed the problem "egregious."
Another indicated that the Boeing employees misled the Federal Aviation Administration. "So I basically lied to the regulators (unknowingly)," read one message.
"It wasn't a lie, no one told us that was the case," came the response.
Boeing did not turn the messages over to the FAA until Thursday, federal officials said Friday.
The FAA said in a statement that it "finds the substance of the document concerning. The FAA is also disappointed that Boeing did not bring this document to our attention immediately upon its discovery."
FAA administrator Steve Dickson said in a letter to Boeing Friday: "I expect your explanation immediately."
Boeing said in a statement that it had provided Congress a document "containing statements by a former Boeing employee." The company said it "will continue to cooperate" with an investigation by the House Transportation Committee and "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."
The existence of the text messages was first reported by Reuters.