NTSB Rules Out Excessive Voltage as Cause for Dreamliner Battery Fire

By Paul Riegler on 20 January 2013
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Burned APU battery from a JAL Boeing 787

Burned APU battery from a JAL Boeing 787

Investigators from the National Transportation Safety Board announced progress with the investigation of a battery fire on a Boeing 787 Dreamliner in Boston that occurred earlier this month and said on Sunday that they were ruling out excessive voltage as the cause.

The Dreamliner was grounded by aviation authorities and airlines around the world on Wednesday after a second battery-related problem caused a fire on board a Dreamliner aircraft while on a domestic flight in Japan.

The NTSB said that the battery on the Japan Airlines Dreamliner “did not exceed the designed voltage of 32 volts” based on data from the airplane’s flight recorder.  A fire occurred on that aircraft on January 7 while the plane was parked at Boston’s Logan International Airport.  No passengers were on board.

While the news is a sign of progress, it also indicates that the cause of the battery-related problems remains a mystery.

The high-tech Boeing 787 Dreamliner has more electrical systems than earlier aircraft. These systems perform a variety of tasks including de-icing the wings, pressurizing the cabin, and operating hydraulic pumps. In addition, the 787 uses electric brakes while other aircraft have hydraulic ones. The Dreamliner has six generators that produce a total of 1.45 megawatts, enough to power 400 homes.

The aircraft has two main lithium-ion batteries, each roughly twice the size of a standard car battery. One, located in the front of the aircraft, supplies power for the plane’s startup functions and ground operations and also serves as backup power for the electric brakes. The second is in the back of the plane and is used to start the aircraft’s auxiliary power unit (APU), which is a small engine that powers the plane while it is on the ground. Malfunctions have been reported with both batteries.

The investigation of the second battery incident is not as far along and is being managed by Japan’s transportation safety board.  On Friday, safety officials there told the media that overcharging the battery might have caused it to overheat.

Possible outcomes following the conclusion of the various investigations could include one where Boeing would have to redesign its new lithium-ion battery system while another might require a switch back to older, safer battery technology  Either change could cost the aircraft manufacturer millions of dollars and adversely impact the promised 20% in fuel savings that the Dreamliner is now capable of.

Last week’s action was the first time in several decades that the FAA had to ground an entire fleet of planes.  An FAA spokesman at the time said that the agency will require a “corrective action plan” from Boeing which makes the aircraft, and its customers, the airlines, before any flights can resume.  The agency did not set a timetable for the investigation, which, according to industry experts, could take months.

(Photo: National Transportation Safety Board)

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