(Reuters) – Japan Airlines Co Ltd  said it temporarily grounded one of its Boeing 787 Dreamliners at Tokyo’s Narita International Airport on Tuesday after white smoke was spotted outside the plane and a battery cell appeared to be leaking.

The incident raised fresh concerns about the 787’s safety and reliability almost exactly one year after the global Dreamliner fleet was grounded by regulators following the overheating of two batteries, although Boeing said design changes made as a result had worked as planned.

Boeing Co said it was “aware of the 787 issue that occurred Tuesday afternoon at Narita, which appears to have involved the venting of a single battery cell.” Venting is the process of fumes and heat being channeled outside the aircraft when the battery overheats.

“The issue occurred during scheduled maintenance activities with no passengers on board,” said Boeing. “The improvements made to the 787 battery system last year appear to have worked as designed.”

Boeing shares fell 0.6 percent to $139.87 on the New York Stock Exchange.

The incident, which was disclosed by Japan Airlines early on Wednesday local time, came nearly a year to the day after Japan Airlines and All Nippon Airways grounded their 787 fleets after two 787 batteries overheated on two different planes in less than two weeks.

Global regulators grounded the worldwide fleet on Jan. 16, 2013. The 787s remained grounded for more than three months while Boeing redesigned the battery, charger and containment system to ensure battery fires would not put the airplane at risk. The cause of the battery problems has not been determined.

United Airlines, the only U.S. carrier that uses the 787, said: “Our 787s are operating normally and we have not experienced any issues with our batteries.”

Japan Airlines said maintenance engineers who were in the cockpit saw white smoke outside the plane. When they went outside the aircraft the smoke had dispersed.

On returning to the cockpit, the engineers found warning lights indicating possible faults with the main battery and charger. When they checked the battery they found one of eight cells was leaking a liquid.

The plane, due to depart from Narita for Bangkok, was taken out of service, and the 158 passengers due to board the plane were put on a separate 787, JAL said.

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