TOKOYO - Investigators from Japan’s Land, Infrastructure, Transport and Tourism Ministry have determined that a fuel leak in a Japan Airlines 787 was due to flaws in the coating of a fuel-pipe valve. On January 13, jet fuel leaked from the valve as maintenance workers at Narita International Airport were removing fuel from the Boeing Dreamliner 787. An indicator in the cockpit showed the value was closed when it was actually open.

According to an article published in The Japan Times, officials from the Land, Infrastructure, Transport and Tourism Ministry asked the valve manufacturer to look into the problem. The manufacturer found that an unnecessary coating was applied to the valve, which caused its motor switch not to function properly. The same plane had leaked fuel earlier in January at Boston’s Logan International Airport. An investigation into that issue discovered that a different valve had failed to close due to a foreign substance stuck in the fuel tank.

Japan's Transport Ministry said it believed the manufacturing process led to deficiencies in the way electrical-insulating coating was applied to the mechanism that open and close the fuel-tank valve.

Investigators also found foreign matter on a switch that operated the same mechanism, causing it to send a signal that the valve was closed when it was still half open, leading to the leak.

In a press conference, Akihiro Ohta, Minister of Land, Infrastructure, Transport and Tourism, stated, “The problem of fuel leaks has been cleared up.”

The Wall Street Journal reports that the ministry's air safety regulators instructed Japan Airlines and All Nippon Airways Co. to conduct more rigorous valve checks each time the aircraft flies or during inspections.

The valve issues are among a number of problems that have plagued the Boeing’s 787 Dreamliner aircraft. The planes have been grounded worldwide since a 787 operated by All Nippon Airways Co. made an emergency landing after smoke in the cockpit. That incident has been linked to the 787's lithium ion batteries.