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Sun 21 Jul 2013 09:39 AM

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Dreamliner probe looks at condensation, wiring

The Boeing jet was grounded for three months this year after two incidents involving overheated lithium-ion batteries

Dreamliner probe looks at condensation, wiring
An ANA Boeing 787 Dreamliner sits in front of the newly opened Everett Delivery Center April 3, 2013 in Everett, Washington. The new 180,000 square feet facility is triple the size of the previous delivery center. (Getty Images)

investigating the fire on an Ethiopian Airlines 787 in London earlier this month
are focused on how condensation in the plane and a possible pinched wire in an
emergency beacon may have sparked the blaze, according to people familiar with
the probe.

The US Federal
Aviation Administration said at the weekend it will call for inspections of the
beacons made by Honeywell on Boeing Co 787 jetliners, but stopped short of
requiring airlines to disable or remove the devices, as British authorities
investigating the fire had recommended.

The FAA said
inspections should ensure wires are properly routed, and should look for pinched
wires or signs of unusual moisture or heat. It gave no further details on how
those factors may have contributed to the fire.

But one source close
to the inquiry told Reuters that investigators had found a pinched wire in the
casing of the emergency locator transmitter (ELT) aboard the

The news comes after
the British Air Accidents Investigation Branch (AAIB) on Thursday said the
Honeywell beacon was the likely source of the fire, but said it was still trying
to understand what ignited the plane.

The July 12 fire
rekindled concern in the industry about Boeing's advanced carbon-composite
Dreamliner, which was grounded for more three months this year after two
incidents involving overheated lithium-ion batteries. The AAIB said the London
fire was not related to those batteries.

The Honeywell ELT is
delivered fully assembled and is installed by Boeing. The unit that was involved
in the fire had not been opened, suggesting the pinched wire originated at the
Honeywell plant, according to one person familiar with the

Honeywell declined to
comment. Boeing declined to comment on the investigation but said it is working
with airlines to either inspect or remove the beacons to meet regulatory

Investigators also
are trying to determine if condensation on the plane seeped into the ELT,
triggering a short circuit in the unit's lithium-manganese battery, which is
made by Ultralife Corp, according to people familiar with the investigation. The
sources were not authorized to speak publicly because the probe is still going

Condensation is
normal on all big airliners, but the 787 has a higher level of humidity for
longer periods to make passengers more comfortable, about 15 percent for the 787
compared with 4-5 percent for conventional metal aircraft, Boeing said. The
humidity can be much higher when any plane is on the ground with doors open,
perhaps 95 percent, because it matches the ambient air. At cruising altitude,
however the air is dry and moisture comes mostly from

Water conducts
electricity, and high moisture levels could raise the likelihood of short
circuits. Long-term exposure to moisture can cause corrosion on electrical wires
and batteries.

Boeing's chief 787
engineer, Mike Sinnett, told Reuters that the humidity controller on the 787,
made by CTT Systems AB of Sweden, is designed to "dry out the crown" or upper
fuselage, of the aircraft, and prevent moisture from accumulating. Without the
system "we would wind up having that water stay in the

Sinnett said the
aircraft is designed to combat corrosion, and the main purpose of the CTT system
is to eliminate water because the water's weight cut's fuel

He declined to
comment on the ongoing AAIB probe, but said any investigation is "going to look
at all potential avenues."

The AAIB also is
looking at the placement of the ELT, which is bolted onto a bracket attached to
the frame of the plane - exactly where condensation builds up, one of the
sources said.

humidity and installation - that's the focal point of the investigation," the
source said.

The ELT must pass a
test to prove it can be submerged under one meter of water for one hour. It is
unclear what effect any longer-term condensation buildup inside the plane would
have on the device, which is encased in aluminum, and its battery, the source

The ELT is not
required by U.S. aviation regulations but is mandated by some

Boeing spokesman Marc
Birtel said all 68 787s in operation have the beacons because all its airline
customers chose that option. Boeing installs the beacons in different areas of
the plane, depending on an airline's preference and its home country's

Birtel last week said
Boeing had no plans to switch suppliers and that the company will "continue to
work with the investigators and regulators to devise acceptable mitigating
action if required."

The non-rechargeable,
lithium-manganese batteries in the ELT have been used for decades in products
like digital cameras and pacemakers, because of their long

This month’s fire
came less than three months after Ethiopian Airlines and others resumed flying
the brand-new all composite plane, following the FAA

Investigators are
also looking at what effect the long grounding may have had on the batteries and
electrical systems used on the plane, said one of the

The Ethiopian
Airlines plane sat outside in Africa for months, raising questions about whether
that could have affected the battery in the locator beacon, said the

Two of the sources
emphasized that investigators were continuing a comprehensive review of a
variety of components and issues. But they said the complex interaction of
humidity and wiring on the plane was a clear focus.

One source, who is
close to Boeing, said the 787 may need better isolation of electrical

Investigators have
yet to determine what prompted the lithium-ion batteries involved in the earlier
fire to overheat. Boeing resolved the issue by redesigning those batteries to
better guard against heat buildup, encasing them in fireproof steel boxes and
cutting a vent in the plane to dump smoke and heat away from

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