CHICAGO — Boeing has told 16 of its customers to address a possible electrical issue in group of 737 Max aircraft before using them further.

The Max was grounded worldwide in March 2019 after two crashes killed 346 people. Regulators in the U.S., Europe, Canada, Brazil and other countries cleared the plane to resume flying after Boeing changed an automated flight-control system that played a role in the crashes.

Boeing said Friday that the recommendation was made “to allow for verification that a sufficient ground path exists for a component of the electrical power system.” It did not specify how many aircraft could be involved.

Some customers like Southwest Airlines, which began flying the Max again last month after the grounding order was lifted, maintains a fleet of hundreds of the aircraft.

The company said it’s working closely with the Federal Aviation Administration on the matter.

Shares of Boeing Co., based in Chicago, slipped less than 1% before the opening bell Friday.

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