By Melissa Gray, CNN
(CNN) — The battery that caught fire aboard an empty Boeing 787 Dreamliner in Boston this month was not overcharged, the National Transportation Safety Board said Sunday.
In its third update on the investigation into the cause of the fire, the NTSB said investigators in Washington took X-rays and CT scans of the lithium-ion battery, which powered the plane’s auxiliary power unit. They took the battery apart and are still investigating some of the individual cells.
Investigators said they have also examined several other components from the plane, including wire bundles and battery management circuit boards. They still plan to test items such as the battery charger and the battery management unit, but the board said an examination of the plane’s flight recorder data indicates the APU battery did not exceed its designed voltage of 32 volts.
Aviation authorities worldwide have ordered airlines to stop flying their Dreamliners because of the fire risk associated with battery failures aboard the highly touted aircraft.
The groundings stemmed from a U.S. Federal Aviation Administration directive last week that planes should not fly until the problems are resolved.
The action resulted from recent mechanical and other glitches culminating with the fire in Boston and an emergency landing in Japan last week prompted by a battery alarm. Some of the 129 people aboard reported a burning smell in the cabin, and an alarm indicated smoke in an electrical compartment.
Boeing said Friday it will not deliver any Dreamliners to its customers as it works with the FAA over the battery concerns.
The batteries in question are lithium batteries manufactured by Japan’s GS Yuasa, under a subcontract to France-based Thales, Boeing said. Kyoto-based GS Yuasa says it has dispatched a team to Washington to help in the investigation.
Lithium batteries are lightweight and hold more than twice as much energy as older nickel cadmium batteries, though they also cost about 40% more.
Boeing is using the lithium batteries to electronically assist some of the functions that were previously performed using hydraulics. A lighter plane is more fuel efficient, which is one of the 787’s main selling points.
There is no need to drain lithium batteries fully before recharging, meaning less maintenance, though they are subject to catch fire if overcharged.