Expectations by The Boeing Company its ill-starred 737 MAX jetliner might again be flying passengers worldwide by December evaporated Wednesday when the U.S. Federal Aviation Administration (FAA) discovered a new flaw similar to the one that led to two fatal crashes of this plane over the past 15 months.

FAA test pilots evaluating Boeing’s software fixes to the faulty automated flight control system called MCAS (Maneuvering Characteristics Augmentation System) discovered this new glitch that can also push the plane downward, which is also what MCAS did in the fatal crashes of two 737 MAX 8s.

In a statement about this new issue, the FAA said it recently found a potential risk “Boeing is required to mitigate."

Sources cited by media said a series of simulator flights to test new MCAS software fixes developed by Boeing revealed the flaw. This troubling development is expected to further delay the aircraft's recertification and return to service.

More specifically, FAA pilots discovered the failure of this single microprocessor could push the nose of the 737 MAX toward the ground. It’s unclear at this time if the microprocessor played a role in the Indonesian and Ethiopian crashes.

During simulator tests, the pilots to their horror discovered it was difficult for them “to recover in a matter of seconds,” according a media source. "And if you can't recover in a matter of seconds, that's an unreasonable risk."

boeing 737 max
A grounded Boeing 737 MAX 8 passenger plane of the Norwegian low-cost airline Norwegian is parked at the tarmac at Vantaa airport in Vantaa near Helsinki, Finland on March 13, 2019. - A number of countries have banned Boeing's 737 MAX 8 medium-haul workhorse jet from their airspace in response to the Ethiopian Airlines crash that killed all 157 people on board. HEIKKI SAUKKOMAA/AFP/Getty Images

Boeing engineers are now trying to fix this new glitch, which has led to another delay in recertifying the 737 MAX 8. They’re trying to figure out if the microprocessor glitch can be fixed by reprogramming the software.

Boeing got ahead of this new problem this time, saying the safety of its airplanes is its highest priority.

“We are working closely with the FAA to safely return the MAX to service," said Boeing in a statement.

On June 3, Boeing CEO Dennis Muilenburg said he expected to get a green light from the FAA to again fly the 737 MAX by the end of the year. The FAA grounded the 737 MAX 8 and 9 in mid-March after the crashes of Lion Air flight 610 in October 2018 and Ethiopian Airlines flight 302 in March that killed 346 people in total.