Japan Airlines has grounded another Dreamliner jet after "white smoke" was seen outside the cockpit window during maintenance, a year after a months-long global grounding over battery problems.
JAL said a technician at Tokyo's Narita airport, who was working on the plane before its departure to Bangkok on Tuesday afternoon, noticed what appeared to be smoke outside the cockpit window and then a battery system warning.
An investigation found one of the eight lithium-ion cells in the plane's battery system had leaked, but its safety valve, which is designed to release excessive pressure, was properly open.
"The temperature of the cell was high. We believe it caused white smoke, which could be smoke or vapour," a JAL spokesman said.
The grounded plane was replaced with another Dreamliner, which left as scheduled, carrying 169 passengers and crew.
"We are making sure of the safety of every plane before its departure. We will continue regular flights [with Dreamliners]" said Norihisa Hanyu from the airline.
The incident was the latest for the Dreamliner since the trouble-plagued aircraft returned to service in the middle of last year following a months-long worldwide grounding.
Boeing said the "improvements made to the 787 battery system last year appear to have worked as designed".
Boeing admitted in April that despite months of testing it did not know the root cause of the problems. It rolled out modifications it said would ensure the issue did not recur, redesigning the battery and charger system and adding a steel box to prevent burning. Since then, Dreamliners have experienced a series of minor glitches, including a fault with an air pressure sensor and the brake system.
In October, unflushable toilets caused JAL pilots to turn their plane around just after it left Moscow bound for Tokyo.
JAL's domestic rival All Nippon Airways also said yesterday it would continue flying the plane. The pair are the aircraft's two biggest customers and have invested heavily in its success.