Federal prosecutors are preparing to indict a former Boeing test pilot suspected of misleading aviation regulators over the safety issues blamed for two fatal 737 MAX crashes, the Wall Street Journal reported on Thursday.

Mark Forkner was the lead contact between the aviation giant and the United States' Federal Aviation Administration over how pilots should be trained to fly the planes, the Journal said.

According to documents published in early 2020, Forkner withheld details about the planes' faulty flight handling system known as the Maneuvering Characteristics Augmentation System, or MCAS -- later blamed for both crashes -- from regulators.

The 737 MAX was formally certified in March 2017, but was grounded worldwide for 20 months following two crashes in October 2018 and March 2019 that killed 346 people.

Boeing's 737 MAX was grounded for 20 months worldwide in March 2019 after 346 people died in two crashes
Boeing's 737 MAX was grounded for 20 months worldwide in March 2019 after 346 people died in two crashes AFP / Olivier DOULIERY

The MAX was allowed to fly again at the end of 2020, once the MCAS software was modified.

Boeing has acknowledged its responsibility in misleading regulators and agreed to pay more than $2.5 billion dollars to settle certain lawsuits.

Neither the US Justice Department nor Forkner's lawyer responded to requests for comment.

The Wall Street Journal said it was not clear what charges Forkner would face.