Federal investigations said Sunday that they had ruled out excessive voltage as the cause of a battery fire on a Boeing 787 in Boston earlier this month, widening the mystery into what led to the grounding of the world’s most technologically advanced jet after a second battery-related incident last week.
With investigators focused on the plane’s lithium-ion batteries, the National Transportation Safety Board said an examination of the data from the plane’s flight recorder indicated that the battery “did not exceed the designed voltage of 32 volts.” The fire aboard a Japan Airlines plane on Jan. 7 at Logan International Airport in Boston occurred after the passengers had gotten off.
Last week, a battery problem on another 787 forced an All Nippon Airways jetliner to make an emergency landing in Japan. That incident prompted aviation authorities around the world to ground the plane, also known as the Dreamliner. The Federal Aviation Administration said last week that it would not lift the ban until Boeing could show that the batteries were safe.
But with investigators on a global quest to find out what went wrong, the safety board’s statement suggested that there might not be a rapid resumption of 787 flights. The 787 first entered service in November 2011 after more than three and a half years of production delays. Eight airlines currently own 50 787s, including United Airlines.
On Friday, Japanese safety officials, who are in charge of investigating the second battery incident, suggested that an overcharged battery might have caused it to overheat. Pilots decided to make an emergency landing 20 minutes after takeoff after receiving several alarms about the battery and smelled smoke in the cockpit.
That investigation is conducted by Japan’s transportation safety board. American investigators are assisting in the inquiry.
The GS Yuasa Corporation of Japan, one of the world’s leading lithium ion manufacturers, makes the batteries for the 787, and Thales, of France, makes the control systems for the battery. The battery is part of a complex electrical system that powers the 787. Like many other components and structures, Boeing outsourced much of the manufacturing to partners around the world.
The safety board typically conducts investigations through a process of elimination, and rules out possible causes along the way.
It said that the lithium-ion battery that powered the auxiliary power unit, a small jet engine that is used on the ground, had been examined in the safety board’s Materials Laboratory in Washington.
The battery was first X-rayed and put through a CT-scan. Investigators then disassembled it into its eight individual cells for detailed examination and documentation. Three of the cells were selected for more detailed radiographic examination to view the interior of the cells.
Investigators have also examined several other components that they removed from the airplane, including wire bundles and battery management circuit boards as well as the battery management unit, the controller for the auxiliary power unit, the battery charger and the power start unit.
On Tuesday, investigators will convene in Arizona to test and examine the battery charger and download nonvolatile memory from the auxiliary power unit controller. Several other components have been sent for download or examination to Boeing’s facility in Seattle and manufacturer’s facilities in Japan.
N.T.S.B. Rules Out a Cause for Battery Fire on 787 Dreamliner
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N.T.S.B. Rules Out a Cause for Battery Fire on 787 Dreamliner
