Text messages released Friday indicate Boeing was warned about problems with 737 Max jets during simulated flights in 2016.

The text messages were handed over to safety regulators Thursday as investigations surrounding the Lion Air and Ethiopian Airline crashes continue. The messages were between employees at Boeing involved in simulation flights and testing to ensure the 737 Max, which have been taken out of service, was ready for use. However, the texts proved otherwise and highlighted the flight control issues that would cause both fatal crashes.

“It’s running rampant in the sim,” pilot Mark Forkner said in a text to a fellow employee, Reuters reported.

Forkner was one of the pilots testing the maneuvering characteristics augmentation system, or MCAS, designed to help address drift and avoid stalls. It’s believed problems with the system led to the both Lion Air and Ethiopian Airline flights going into uncontrolled nosedives, killing 346 people.

“I basically lied to the regulators [unknowingly],” Forkner said in another text. Another employee responded, saying: “It wasn’t a lie. No one told us that was the case.”

The texts are dated November 2016. However, it was also revealed Forkner had approached the Federal Aviation Administration about removing mentions of the MCAS system from the Max’s flight manual. The FAA approved it, believing at the time the system would activate on rare occasions and didn’t present any potential flight risk.

In response to the texts, FAA Administrator Stephen Dickson sent a letter to Boeing chief executive Dennis A. Muilenburg Friday, demanding to know why the texts weren’t handed over sooner.

“I expect your explanation immediately regarding the content of this document and Boeing’s delay in disclosing the document to its safety regulator,” Dickson wrote, the New York Times reported.

Muilenburg is scheduled to appear at a Senate Commerce Committee hearing on Oct. 29 and before a House panel Oct. 30.