Washington CNN Business  — 

Boeing’s troubled 737 Max has run into a new glitch.

During a recent technical review involving the Max, Boeing observed an issue with the plane’s flight computers, according to a source familiar with the matter.

The source said the issue is not related to the software revisions Boeing made to address the cause of two fatal crashes that killed 346 people, and would not occur during flight. The Max has been grounded since March following the second of those crashes.

The computer issue was observed when booting up the computers on a Max and involves the so-called software power up monitoring function, which checks for anomalies when turning on the computers. It’s similar to the steps any computer might make when first turned on. The source said the process of turning on the computers is performed when the plane is on the ground, rather than in flight.

The source said the test was intended to find any issues like this one and that Boeing would fix the problem.

Boeing has been working on a software fix for the safety system that is believed to be the cause of the two fatal crashes. The source could not say whether this latest issue would impact the company’s submission of the software changes to the Federal Aviation Administration.

“We are making necessary updates and working with the FAA on submission of this change, and keeping our customers and suppliers informed,” Boeing said in a statement. “Our highest priority is ensuring the 737 MAX is safe and meets all regulatory requirements before it returns to service.”

ABC News first reported the issue with the flight computers.

The Max crisis has cost Boeing billions of dollars. The company reported more cancellations than new business in 2019, and its order book for the troubled 737 Max shrank by 183 jets.

On Friday, Fitch Ratings downgraded the company’s long-term ratings to ‘A-’ from ‘A’.