MIAMI — A Japan Airlines (JAL) Boeing 787 battery was found smoking during a pre-flight inspection at Narita Airport in Tokyo on Tuesday.

Airline maintenance crews detected a fault in the battery and charger while in the cockpit. A worker noticed white smoke out the window, and found that one of the battery’s safety relief valves had vented. A liquid was found inside the battery container, though the substance type was unclear.

Boeing released a statement around 9AM PST, declaring that a single battery cell appears to have vented. They added that “improvements made to the 787 battery system last year appear to have worked as designed.”

The airplane, originally bound for Bangkok, was taken out of service for an investigation. Another Boeing 787 was placed on the flight.

JAL has not returned a request for comment.

It was roughly one year ago that a JAL 787 battery caught fire while on the ground in Boston’s Logan International Airport. The incident prompted a still ongoing federal investigation into the incident and the process that led to the controversial lithium-ion battery system receiving approval in the first place. It also was the opening act in a string of incidents that led to the Dreamliner being grounded for over three months in early 2013.

Yet until today the airplane, or at least its batteries, had gone without further issue. That Boeing pointed to the battery fix “working as designed” as evidence of success underscores that the true cause of the incidents remains unknown.