* NTSB pinpoints short circuit in single cell
* Investigators looking at total design of battery
* Battery certification process to be reconsidered
By Jim Wolf
WASHINGTON, Feb 7 An air safety investigation of
a battery fire on a Boeing Co 787 Dreamliner last month
has narrowed the source to one of the battery's eight cells,
though the actual cause of the fire is not yet known, the head
of the National Transportation Safety Board said on Thursday.
Regulators should now reconsider the assumptions used to
certify the plane's lithium-ion batteries, Deborah Hersman said
at a news conference in Washington, adding to the uncertainty of
when the cutting-edge plane might be cleared to fly again.
The 50 Dreamliners in service were grounded worldwide on
Jan. 16, after a series of battery incidents, including a fire
on a parked 787 in Boston and an in-flight problem on another
plane in Japan. The groundings have cost airlines tens of
millions of dollars, with no end in sight.
The NTSB probe is focused on the Boston fire, and Hersman
said investigators now believe multiple short circuits in a
single cell may have led to a chemical reaction known as a
thermal runaway, which cascaded to other cells and spread the
Hersman said a review is needed of the "special conditions"
under which aviation regulators approved Boeing's use of this
particular battery technology on the 787, a decision that has
lately come under close scrutiny.
"There have now been two battery events resulting in smoke,
less than two weeks apart, on two different aircraft. This
investigation has demonstrated that a short-circuit in a single
cell can propagate to adjacent cells and result in smoke and
fire. The assumptions used to certify the battery must be
reconsidered," she said.
The NTSB plans to issue an interim factual report in 30
days, though the decision on returning the plane to regular
flight rests with the Federal Aviation Administration.
As Hersman was addressing the news conference in Washington
DC, the first 787 flight since mid-January left Texas for
Washington state, a so-called ferry flight being run under heavy
conditions to see if any battery problems crop up.
According to flight tracking website FlightAware, it left
Dallas at 9:25 a.m. CST (1525 GMT) for the nearly
three-and-a-half hour flight to Everett, Washington. Ultimately
scheduled for delivery to China Southern Airlines,
the aircraft has not yet been handed over to the customer.
The Federal Aviation Administration said Wednesday it had
approved the flight, which differed from Boeing's request to run
a series of test flights. It placed a number of conditions on
the one-off trip, mostly having to do with testing and
monitoring the plane's battery.
While the investigation continues, Boeing is pursuing
multiple ways to mitigate and contain a fire, if one starts in
the batteries, one source familiar with the probe told Reuters.
Three or four varying approaches would be pursued to ensure the
batteries did not breach their containment systems, even if they
caught fire, said the source.