By Andy Pasztor
The Wall Street Journal
Oct. 16, 2013 8:02 p.m. ET
Years
after aviation-safety experts thought they had eliminated the danger of
airliner engines abruptly shutting down from internal ice accumulation,
the same airborne hazard is showing up on a new generation of Boeing
Co. jumbo jets.
The Chicago plane maker and General Electric Co.,
whose engines are installed on the biggest and newest Boeing 747 model,
are now working together on fixes to prevent ice buildup that can
prompt the giant airliner's engines to temporarily malfunction or even
stop working while cruising roughly 7 miles, or 41,000 feet, above the
earth.
A GE spokesman said there are proposed software
changes—which still need to be tested and then approved by the Federal
Aviation Administration—designed to detect the presence of ice crystals
in the atmosphere and eject the tiny particles before they form a
coating deep inside engines that can melt or break into chunks.
In
extreme cases, the accumulation of ice inside an engine could cause
damage to turbine blades or sudden dousing of the ignition system,
though there haven't been any reported accidents.
The problems
underscore difficulties regulators and industry officials face in
resolving some persistent engine-safety issues. The reliability of jet
engines has improved exponentially over the last few decades,
contributing to steadily lower accident rates across the U.S. and other
regions. Some older GE designs, for instance, have racked up outstanding
safety records of one airborne engine shutdown per every million flight
hours.
Still, challenges with the GEnx-2B engines on extra-long
747 aircraft—known as 747-8s—highlight complex and nagging icing hazards
that once again are forcing industry leaders and an international
research team to scramble for answers. Before the partial government
shutdown, according to industry officials, the FAA was moving toward
mandating modifications to the 747-8's computerized engine controls and
making plans to warn pilots about susceptibility to internal engine
icing while flying over storm-prone regions at roughly 40,000 feet.
Previously,
experts believed such icing occurred primarily below 25,000 feet. From
the mid-1990s to the end of 2011, the FAA and various engine
manufacturers investigated ice-crystal buildups affecting more than 100
big jets around the world, including at least 14 instances of
dual-engine shutdowns, called "flameouts." Starting in 2007, the
industry successfully rolled out various modifications to counter those
hazards.
The latest engine problems, however, caught GE, Boeing
and the FAA by surprise, partly because they cropped up on a different
engine model at significantly higher altitudes than anticipated,
according to industry officials. Moreover, the recent incidents often
occurred in clear air without clouds or signs of nearby storms.
Since
the spring GE has investigated four 747-8 freighters with icing-related
engine problems, including a Russian AirBridge Cargo plane that had two
engines surge and a third engine dramatically lose thrust July 31 while
flying at 41,000 feet over China. Russian investigators said three of
its four engines suffered damage, but the plane landed safely.
Boeing's
747-8 passenger version, dubbed the Intercontinental, is the world's
longest commercial aircraft and can carry more than 460 passengers in
three classes. Customers for the 747-8 include Deutsche Lufthansa AG
and Cathay Pacific Airways Ltd.
On Wednesday, a GE spokesman
said all of the 747-8 incidents occurred around "unique convective
weather systems" such as unusually large thunderstorms reaching high
altitudes. Only the AirBridge Cargo incident, which intensified industry
concern, "resulted in engine damage," according to GE.
Airlines
have been "experiencing a growing number of ice-crystal" incidents,
according to the GE statement, reflecting more long-range jets crossing
over tropical regions of the world. Engine flameouts and thrust
reductions, typically happen quickly, with virtually no warning,
according to safety experts.
Boeing said it is "working closely" with GE "on the software solution." The FAA didn't have any immediate comment.
Such
icing emergencies remain rare. "I'm not alarmed by an event that we are
learning from," said Mark Rosenker, former vice chairman of the
National Transportation Safety Board, adding that experts "continue to
look at any type of incident to get as close to 100% engine reliability
as possible."
A different category of icing hazard has dogged
some of Boeing's widely-used 777 widebody jets since 2008, when ice
blocked the fuel-system plumbing of a British Airways PLC jet powered by
Rolls-Royce engines that ended up crashing on final approach to
London's Heathrow Airport. After extensive investigation and ground
tests, experts determined the accident stemmed from a type of icing that
didn't occur inside engines.
Separately, over the years Boeing
has dealt with a string of potentially dangerous overheating incidents
and chronic structural damage to parts called thrust reversers attached
to Boeing 777 engines manufactured by Rolls-Royce PLC. Used to help jets
slow down after landing, 18 of the devices have suffered fractures or
failures of their inner walls over the past 10 years, according to a
Boeing spokeswoman. Since 2005, she said the company has "communicated
extensively" with 777 operators and issued nonbinding recommendations to
check or replace the suspect parts, but "we're unable to confirm how
many inspections or modifications have taken place."
But the
thrust-reverser issue may be coming to a head. In August, as part of a
report on a Royal Brunei Airlines 777 that lost part of its reverser
after takeoff from London, British accident investigators said Boeing
told them the FAA "may mandate inner wall replacement on all Rolls-Royce
powered Boeing 777 aircraft."
An FAA spokeswoman didn't have an immediate response, and a spokesman for Rolls-Royce declined to comment.
Source: http://online.wsj.com
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