Boeing's embattled 737 Max aircraft was reportedly nearly finished being redesigned in June when a simulated flight of the plane almost crashed.

Bloomberg reports that a computer glitch caused the simulated plane to aggressively dive in a way that resembled how fatal crashes in Ethiopia and Indonesia occurred earlier in the year.

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The simulated failure led to an extensive redesign of the plane's computers, which has resulted in a lengthy delay of the plane returning to action.

All 737 Max aircraft were grounded on March 13 after the two crashes killed a combined 346 people.

Sources told the news outlet that the new glitch goes beyond the initial problem that had led to the crashes.

Originally, Boeing engineers had aimed to only fix the aircraft's maneuvering characteristics augmentation system, but the setback has caused the airline company to rework the 737 Max's twin computers, a process that is considerably more involved.

John Hansman, an aeronautics and astronautics professor at the Massachusetts Institute of Technology, isn't involved in the fix but told Bloomberg that "it's really complicated," referring to the process of redesigning airplane software.

“It totally makes sense why it’s taking longer.”

In addition to the repair process being more complicated, the number of safety hoops that Boeing has to jump through before the Federal Aviation Administration (FAA) will clear the plane to fly again has also increased.

“Where before you may have had 10 scenarios to test, I could see that being 100,” former Boeing engineer Peter Lemme told the publication.

The delays and added fixes have led to tensions between the aircraft manufacturer and the FAA, which has prompted the federal agency to repeatedly ask Boeing for more documentation regarding the redesign process, Bloomberg reports.

In a statement, Boeing said that it gave documents to FAA officials “in a format consistent with past submissions.”

“Regulators have requested that the information be conveyed in a different form, and the documentation is being revised accordingly,” the statement continued.

“While this happens we continue to work with the FAA and global regulators on certification of the software for safe return of the MAX to service.”

Boeing has said that it expects the 737 Max to return to service in January.