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Boeing has found another software issue that needs fixing on its 737 Max jets, and the discovery explains why the aircraft maker is delaying its schedule for getting the planes back in the air.

A Boeing spokesman on Friday called it a "relatively minor issue" and said the plane maker already has a fix in the works.

The spokesman, Charles Bickers, said the latest issue is not part of flight-control that Boeing has been working to upgrade for months.

That software, known by its acronym MCAS, is suspected in two recent deadly crashes in Indonesia and Ethiopia that led regulators to ground the worldwide last month.