TOKYO--Japanese aviation officials said Wednesday that flight
data from a Boeing Co. (BA) Dreamliner jet that made an emergency
landing in central Japan last week has shown no evidence so far
that the battery was overcharged, a finding that sheds a new light
onto what went wrong on the flight.
Norihiro Goto, the chairman of the Japan Transport Safety Board,
told reporters at a press conference that data acquired from the
Dreamliner's digital flight data recorder showed there was nothing
"abnormal" in the battery's voltage level before a series of alarms
went off in the plane's cockpit. The pilots of the plane, operated
by All Nippon Airways Co. (9202.TO), decided to make an emergency
landing because of a smoldering smell emanating from the electrical
compartment below the deck where the highly flammable lithium-ion
battery was installed.
The latest finding potentially changes the direction of the
Japanese investigation into what went wrong with the plane and
brings it more in line with what U.S. investigators have found in a
similar incident in Boston. In that incident, a battery on a parked
Dreamliner operated by Japan Airlines Co. (9201.TO) caught
fire.
The U.S. National Transportation Safety Board said earlier this
week that the JAL 787's battery "did not exceed its designed
voltage." One of the Japanese investigators looking into the ANA
Dreamliner incident said last week that the burn marks on the
charred battery suggested overcharging, as among the more likely
causes initially leading to the impression that the U.S. and
Japanese probes were headed in different directions. Data from the
aircraft's digital flight data recorder was not available at the
time.
The twists and turns of the U.S and Japan probes -- run
separately but with the cooperation of the other -- underscore the
difficulty of troubleshooting the advanced electrical system that
powers Boeing's flagship jet, celebrated at its launch for its
revolutionary features. Among them is the Dreamliner's heavy
reliance on electrical systems to perform many functions that were
previously handled mechanically. The plane, for instance, moves
parts of wings electrically instead of with hydraulic devices.
Two engineers from Thales S.A. (HO.FR) of France joined the
investigative team in Japan on Tuesday, transport ministry
officials said Wednesday. Thales designs and makes electrical
systems for the aerospace and transport industries--including the
battery-operation system for the Boeing (BA) 787. Engineers with GS
Yuasa Corp. (6674.TO), the maker of the 787's lithium-ion
batteries, are also involved of the investigation.
The U.S. Federal Aviation Administration and other global
aviation regulators last week grounded all Dreamliners until
regulators are convinced the battery systems are safe.
The data found on the digital flight data recorder of the ANA
Dreamliner showed that the output voltage of the battery did not
exceed the maximum 32 volts, said Mr. Goto of the JTSB on
Wednesday. It had stayed at 31 volts before suddenly dropping and
then moving up and down, indicating that overcharging may not have
been the cause of the incident.
But JTSB officials cautioned that there is still insufficient
data to rule out any potential causes of the incident entirely,
since it's still unclear whether the voltage fluctuations were a
cause or symptom of the problems.
One unknown is whether there was excess voltage coming into the
battery, said Mr. Goto. The data showed only the voltage of the
battery output, not inflow of electricity into the battery, he
said.
The JTSB will also have to investigate the battery charger to
figure out whether there may have been overcharging from the
charger, Masahiro Kudo, a director general of the JTSB told
reporters after the press conference.
The flight data also suggested that the battery wasn't used
during the flight. Instead, power was supplied by four generators
connected to the engines. The voltage level remained stable
throughout the flight until the alarms went off.
Mr. Goto said the next step of the investigation will be to
figure out why the voltage suddenly dropped.
Write to Yoshio Takahashi at yoshio.takahashiy@dowjones.com
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