Instant messages from 2016 suggest that Boeing may have misled the Federal Aviation Administration about a controversial safety system of its grounded 737 Max jets, Reuters reports. The messages, between two Boeing employees, raise questions about the safety of the MCAS software that is thought to have brought down two 737 Max jets, killing a total of 346 passengers.

In the messages, a Boeing pilot named Mark Forkner griped that the MCAS system was making the plane difficult to fly the 737 Max in simulation, according to a similar report in The New York Times. “Granted, I suck at flying, but even this was egregious,” Forkner said, according to a transcript reviewed by the Times.

“Granted, I suck at flying, but even this was egregious”

Forkner, who is the chief technical pilot for the 737, went on to admit that he may have misled safety regulators about the plane. “I basically lied to the regulators (unknowingly),” he said, according to the Times. The messages are from November 2016, eight months before Forkner made a request to the FAA to remove mention of MCAS from the pilot’s manual. The FAA, believing MCAS could only be activated in rare cases, approved the request.

Boeing discovered the messages “months ago,” but only recently turned them over to the Department of Transportation. In a letter to Boeing CEO Dennis Muilenburg, FAA Administrator Steve Dickson calls the messages “concerning” and demands to know why Boeing delayed turning them over to regulators. Muilenburg is expected to testify before Congress later this month.

MCAS, which stands for Maneuvering Characteristics Augmentation System, is a software unique to Boeing’s 737 Max jets that takes sensor data to determine how much the plane’s nose is pointing up or down relative to oncoming airflow. When MCAS detects that the plane is pointing up at a dangerous angle, it can automatically push down the nose of the plane in an effort to prevent the plane from stalling.

A preliminary report from Indonesian investigators indicates that Lion Air 610 crashed because a faulty sensor erroneously reported that the airplane was stalling, triggering the MCAS system which then tried to point the aircraft’s nose down so that it could gain enough speed to fly safely.

The report comes as Boeing is pushing to get the Max jets back in the air. The planes have been grounded since March 2019, when Ethiopian Airlines 302 went down. The move put enormous strain on carriers, which struggled to shift the planes out of service while minimizing the impact on customers. Boeing is expected to submit its final certification package to the FAA later this year.

The FAA did not immediately respond to a request for comment. A spokesperson for Boeing provided the following statement: