- The FAA said Boeing withheld the messages between employees for months, sending shares lower.
- The incident ramps up pressure on Boeing and CEO Muilenburg about the planes.
- Boeing and the FAA are facing several investigations about the 737 Max's design and certification.
The Federal Aviation Administration said Boeing withheld "concerning" messages from 2016 between employees about the 737 Max, deepening the manufacturer's crisis over the jets that have been grounded worldwide since March.
A Boeing test pilot complained in one of the messages that a flight control system, known as MCAS, was difficult to control, the New York Times reported.
"It's running rampant" in the simulator, he told a colleague, according to a transcript reviewed by the NYT. "Granted, I suck at flying, but even this was egregious."
That system is at the heart of investigations into two fatal crashes. Investigators have implicated the system in both crashes — a Lion Air 737 Max that went down in Indonesia in October 2018 and an Ethiopian Airlines plane of the same model that crashed in March.
That system malfunctioned on both flights, repeatedly pushing the planes' noses down until their final, fatal dives. All 346 people on both flights were killed.
Pilots at airlines including American complained after the crashes that it did not know about the system, known as MCAS, until after the first crash.
Boeing shares were down more than 4% in afternoon trading, shaving 107 points off the Dow Jones Industrial Average.
The messages add to pressure already piling up on Boeing and CEO Dennis Muilenburg. The company and the FAA are facing several investigations into the plane's design and software.
The company's board removed Muilenburg as chairman last week, saying the division of the two roles will help him focus on bringing the plane back to service. Muilenburg will face lawmakers for the first time since the crashes in a House transportation committee hearing scheduled for Oct. 30.
The FAA said Boeing discovered the messages "some months ago." The FAA, which first certified the planes in 2017, said it is "disappointed that Boeing did not bring this document to our attention immediately upon its discovery," the agency said, adding that it is "reviewing this information to determine what action is appropriate."
The FAA turned over the instant messages to U.S. lawmakers and the Department of Transportation Inspector General, the agency said.
"Over the past several months, Boeing has been voluntarily cooperating with the House Transportation & Infrastructure Committee's investigation into the 737 MAX. As part of that cooperation, today we brought to the Committee's attention a document containing statements by a former Boeing employee," Boeing said in a statement.
Boeing has developed a software fix for the software that misfired on the crashes but regulators haven't yet signed off.