Documents released recently by Boeing regarding design and certification of 737 Max airplanes revealed that the employees mocked regulators and admitted flaws with the plane.
In one message, employees mocked the U.S. Federal Aviation Administration (FAA) and touted of having regulators approve the jets without requiring additional pilot training, according to NPR's report published Thursday.
"This airplane is designed by clowns who in turn are supervised by monkeys," wrote one worker in another message.
Boeing's top-selling aircraft model was grounded worldwide after two crashes that cost hundreds of lives, and hit the company billions of dollars financially.
On March 10, Ethiopian Airlines Flight ET-302 crashed shortly after taking off from an Addis Ababa airport, killing all 157 onboard.
The model was also involved in an October crash outside of Jakarta, Indonesia. All 189 people on board Lion Air Flight JT610 were killed.
"I still haven't been forgiven by God for the covering up I did last year," a worker says in 2018, according to the document, suggesting the staff misled regulators about potential problems of the model after flight simulators.
"Would you put your family on a Max simulator trained aircraft? I wouldn't," says one employee to another, who responds, "No."
The company defended itself in a statement released on Thursday by saying the issue has been reviewed carefully and they are confident that all of Boeing's MAX simulators are functioning "effectively".
Boeing stressed these communications brought in December to the FAA's attention in furtherance of the company's "commitment to transparency with its regulator and strong safety oversight of our industry."
Calling the internal conversations are "completely unacceptable," the company added that those communications do not reflect their brand.
The statement concluded with saying those actions will bring disciplinary consequences once the necessary reviews are completed.
