Boeing was aware of troubling instant messages between two employees regarding their communications with federal regulators over a key flight-control system on its now-grounded 737 Max jet, but the company waited months to disclose them.
Federal Aviation Administration chief Steve Dickson demanded an explanation from Boeing CEO Dennis Muilenburg in a letter Friday.
Boeing, in a prepared statement, said the document contained the communications of a former employee. It did not identify the person.
The company didn't explain why it waited months before turning over the document, but said it was cooperating with the congressional investigation into the Max.
The FAA said it "finds the substance of the document concerning" and is disappointed that Boeing waited months before bringing them to the agency's attention.
The messages point to potential problems in a flight-control system called MCAS, according to a person familiar with them and who spoke anonymously because they were not authorized to discuss the issue.
MCAS has been implicated in preliminary investigations into a pair of crashes in Indonesia and Ethiopia that killed 346 people and led regulators worldwide to ground the Max.
The disclosure of the internal Boeing communications comes just a week after international regulators faulted the company for not doing more to keep FAA informed about MCAS, a new automated flight system not included in previous versions of the 737.
In his terse, three-sentence letter to the Boeing CEO, FAA chief Dickson wrote, "I expect your explanation immediately regarding the content of this document and Boeing's delay in disclosing the document to its safety regulator."
Boeing shares (BA) tumbled 5% on the disclosure of the communications that the FAA had been unaware of.
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