NTSB: 787 battery investigation still weeks from pin-pointing cause

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Three weeks after US officials grounded the Boeing 787, the chairman of the National Transportation Safety Board (NTSB) believes the ongoing probe of the battery failures is still "weeks" away from determining a root cause.

The NTSB's Deborah Hersman has scheduled a press conference on 7 February to provide a full update on the 787 investigation. Meanwhile, the Federal Aviation Administration (FAA) is continuing to consider a request from Boeing to restart flight tests.

Boeing, however, is still far away from testing any solution developed in response to the results of the NTSB investigation.

Speaking at a breakfast hosted by the Christian Science Monitor in Washington DC, Hersman said that finding a root cause of the battery failures will probably take multiple more weeks.

Investigators in the USA and Japan have detected signs of thermal runaway and short circuit within the 787's two eight-cell, 32V lithium-ion batteries. But the investigation teams are still unsure what is causing the batteries to short-circuit and start an escalating and uncontrollable thermal reaction that causes the batteries to melt and in one instance catch fire.

Last week, Japanese investigators found no meaningful clues after inspecting the GS Yuasa factory that makes the batteries. Both Japanese and US investigators have also found no evidence that the batteries were over-charged before the short-circuit occurred.

In her remarks, Hersman also appeared to challenge comments by several experts, including SpaceX founder and Tesla electric car maker Elon Musk, who told Flightglobal in an e-mail last week that the 787 battery design was "fundamentally unsafe".

Hersman countered, however, that there was nothing inherently unsafe about the 787 battery design. Boeing selected the lithium-ion battery for the 787 in 2005, making the widebody the commercial aviation industry's trailblazer for such a battery to serve as an emergency power supply and starter for an auxiliary power unit.

The 787 battery is divided into eight cells, with each cell rated to be charged at 3.7V, or nearly twice the capacity of nickel-cadmium batteries that have been the industry standard since the early 1960s.

Boeing, however, selected a particularly powerful configuration for this lithium-ion battery. Each of the eight cells are rated to store 72Ah of electric current, compared to about 3Ah of storage capacity on each of the lithium-ion cells powering Musk's Tesla Roadster.