Faulty batteries were not to blame for the problems experienced by Boeing's 787 Dreamliners, according to Japanese safety inspectors.
Japan's transport ministry announced on Monday that the battery - which was initially considered the likely source of problems on 787s owned by two Japanese airlines - had nothing wrong with it.
The plane's electrical system that monitors battery voltage, charging and temperature, will now be assessed. More than a third of components on the planes are made in Japan.
Transport ministry official Shigeru Takano told the BBC he had found "no major quality or technical problem" with the lithium-ion batteries. Shares in GS Yuasa, which makes the batteries, jumped 5% on the news.
"We are looking into affiliated parts makers; we are looking into possibilities," he added.
The safety investigation started after one of the 787s operated by All Nippon Airways made an emergency landing in Japan when its main battery overheated. Earlier, a battery in a Japan Airlines 787 caught fire while parked at Boston's Logan International Airport.
On 16 January, the Al Nippon flight to Tokyo was forced to land shortly after taking off from Yamaguchi Ube in Western Japan after smoke was seen in the cockpit and an "odd smell" was also reported, according to the ANA.
Five people were injured and one person was taken to hospital.
The US Federal Aviation Administration claimed both batteries had leaked electrolyte fluid, and there had been smoke damage to parts of the aircraft.
The FAA said airlines must demonstrate battery safety before flights could resume, a statement that effectively meant airlines had to ground their 787s.
Only days before a flight from Boston's Logan airport to Tokyo was cancelled after engineers found that around 40 gallons of fuel had been spilled. The 178 passengers and 11 cabin crew on board had to be evacuated and while the plane was towed back to the gate, the cockpit and cabin filled with smoke.
And a third problem, this time with the brakes, was reported earlier in the month.
Boeing, which competes against Airbus of France, has halted 787 deliveries. Boeing has orders for more than 800 Dreamliners.
The 787 is supposed to be the greenest plane in existence - it's the first airliner made mostly from lightweight composite materials that boost fuel efficiency. It also relies on electronic systems rather than hydraulic or mechanical systems to a greater degree than any other airliner.
Boeing chief executive Jim McNerney is due to address shareholders on 30 January, when the company delivers its 2012 results.
Where can you find Boeing's Dreamliners?
Air India: 6
All Nippon Airways (Japan): 17
Ethiopian Airlines: 4
Japan Airlines: 7
LAN Airlines (Chile): 3
Lot Polish Airlines: 2
Qatar Airways: 5
United Airlines (US): 6
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