Boeing announced it’s working with the FAA on an additional software problem on its grounded 737 MAX jetliner. This problem involves monitors that verify that key systems on the plane are functioning.

One source tells the Associated Press that during a recent test, one of the monitors did not start when it was supposed to.

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“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.”

The issue was discovered during a technical review that normally happens near the end of the software-development process, reports The Wall Street Journal. That could be a sign Boeing is close to finishing needed changes to get the 737 MAX planes back in the air.

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The two recent crashes have resulted in all 737 MAX jets being grounded. The Lion Air crash out of Indonesia resulted in the death of 189 people and the Ethiopian Airlines crash led to 157 deaths. It’s believed to be linked to an automated system that pushed the nose of the plane downwards. It’s up to the FAA to decide when the plane can resume flying.

With reporting from MyNorthwest