Prospects for returning the Boeing 787 to flight within days or weeks dimmed as a worldwide grounding in response to battery over-heating problems entered its second week.

US and Japanese safety investigators have ruled out over-charging as a cause for a battery failure and related fire on a Japan Airlines 787 in Boston on 7 January and an overheated battery that forced an All Nippon Airways 787 to make an emergency landing in Japan on 16 January.

Investigators are now focusing on a wide range of other possible causes, including simple defects in manufacturing to more complicated possibilities, such as an electrical architecture that may somehow demand too much discharge from the batteries.

While the investigation continues, the US Federal Aviation Administration is waiting to learn more about the root cause. The agency can then develop the corrective action plans necessary to demonstrate the safety of Boeing's solution to the problem and return the 787 to commercial service. The question now is whether that procedure will take weeks or months to complete, and that timing depends solely on finding out why the batteries are over-heating.

More is being learned about the kind of lithium ion batteries used in the 787. Lithium ion has become a popular power source for an enormous range of electrical applications, ranging from smart phones to electric cars.

As the grounding has raised new questions about the safety of lithium ion batteries, some in the electric car industry are criticizing Boeing for using what they consider a risky chemistry on the 787.

Boeing subcontractor Thales was selected in 2005 to provide an eight-cell, 32V lithium ion battery made by GS Yuasa. At that time, the state-of-the-art chemistry in the battery industry was lithium cobalt oxide (LCO), says Cosmin Laslau, an electric car industry analyst for Lux Research.

Since 2005, the automotive industry has plunged into production of dozens of electric and hybrid cars powered by lithium ion, but have preferred to use safer and less powerful lithium ion chemistries based on manganese or iron phosphate inside of cobalt, Laslau says. Cobalt-based chemistries can become flammable at much lower temperatures than other forms of lithium ion batteries, he adds.

Boeing was understood to be considering a manganese-based chemistry in 2008 to improve the reliability of the 787's batteries, but that idea apparently was dropped. The airframer confirms that the batteries on the 787 that start the auxiliary power unit and serve as a back-up power source are based on the lithium cobalt oxide chemistry.

Source: Air Transport Intelligence news