Boeing final word /RR-Trents
oeing issues warning to 777 operators
A Delta Airlines 777-200ER was flying from Shanghai, China, to Atlanta last
November when its right engine suddenly lost thrust while the plane was
cruising at 39,000 feet over Montana.
The pilots followed flight manual procedures and descended to 31,000 feet,
where the Rolls-Royce engine recovered and responded normally. The flight,
with 15 crew members and 232 passengers, continued to Atlanta and landed
safely.
That incident would likely not have gotten much attention had the same kind
of Boeing jet, with Rolls-Royce engines, not lost all power in both engines
just before landing at London's Heathrow earlier in the year. The British
Airways 777 crash-landed short of the runway. Several passengers were
injured, but none seriously.
Safety experts eventually decided that the British Airways jet, also on a
flight from China, had flown through unusually cold weather at cruise
altitude and ice apparently formed in part of the engine and blocked the
fuel flow.
On Thursday, Boeing sent a notice to all operators of its 777s with Trent
engines made by Rolls-Royce, advising them that it now believes the Delta
and British Airways incidents appear to have been caused by the same thing –
ice blocking the fuel path.
A Boeing spokesman said Tuesday the "all operators" notice contains a series
of precautionary measures that pilots should take during flight to lessen
the chance ice could cause a sudden loss of engine power.
Eventually, the spokesman said, the FAA can be expected to order a
"permanent fix.'' That would likely mean a redesign of part of the Trent 777
engine.
Boeing would not release a copy of the letter it sent last week. The
spokesman said it is not a public document. But the industry magazine Flight
International obtained a copy and said the Boeing letter describes the Delta
and British Airways incidents as likely being caused by "similar factors.''
More than 700 Boeing 777s, a widebody jet that typically carries from 300 to
360 passengers, depending on the model, are in service with airlines around
the world. About 30 percent have Trent engines.
General Electric and Pratt & Whitney also make engines for the 777, but
those have a different design than the Trent engine from Rolls-Royce and are
not thought to be susceptible to the ice problem. The newest 777s built by
Boeing, the best-selling 777-300ER and the ultra-long-range 777-200LR, are
only powered with GE engines.
In September, the Federal Aviation Administration issued a formal
airworthiness directive that required changes in the way ground crews
prepare 777s with Trent engines and how pilots fly them in extreme cold
weather in response to what investigators found in studying the British
Airways crash in January. Shortly before the FAA issued its warning, Boeing
had sent out an "all operators" notice with a series of recommendations
developed to prevent a similar problem on its 777s with Trent engines.
Boeing recommended, for example, that pilots rev their engines when the fuel
temperature falls to 14 degrees Fahrenheit. That would conceivably dislodge
any ice that might be in the fuel line.
Another procedure recommended by Boeing, and ordered by the FAA, called for
the crew to advance the engine throttles to maximum thrust for 10 seconds
before descending on flights that have maintained the same altitude for at
least three hours, if the fuel temperature is below 14 degrees.
Those procedures have been revised in the Boeing bulletin sent last week,
following the Delta incident.
Boeing now recommends that pilots advance engine throttles to maximum thrust
before descending on flights that have maintained the same altitude for two
hours, not three.
Also in its latest notice, Boeing recommends that pilots, during the descent
for landing, reduce engine power to full idle for at least 30 seconds. By
reducing fuel flow, engine oil heat can melt any ice that may have
accumulated.
The FAA, as it did in September, is likely to make Boeing's latest
recommendations mandatory.
The 777 has never had a fatal crash since it entered service with United
Airlines in 1995. But the Delta and British Airways incidents have given
safety experts cause for concern, in large part because they are apparently
dealing with a previously unknown phenomenon.
The British Airways crash occurred Jan. 17, 2008, as the 777-200ER, with 152
passengers and crew members, approached Heathrow after a flight from
Beijing. Both engines failed to respond to autopilot commands for thrust as
the plane approached the airport.
It turned into one of the most puzzling aviation accidents in modern times.
The plane was badly damaged but was mostly intact, so investigators had all
the physical evidence in hand to look for clues. But one thing was missing –
the ice. The key piece of evidence had literally melted away.
Investigators now believe the problem is with the fuel-oil heat exchanger
system on the Trent 777 engine.
Boeing engineers, according to Flight International, have determined by
working in the laboratory that the heat generated by the Rolls-Royce
fuel-oil heat exchanger is not adequate to prevent moisture in the fuel from
freezing. When that happens, ice can form that blocks fuel to the exchanger,
"starving the engines,'' according to the magazine.
The General Electric and Pratt engines on the 777 have a different fuel
system architecture.
"Based on our knowledge of the system configurations, scenario studies and
laboratory test results, we do not believe that immediate action is
necessary or warranted for 777s powered by other engine types or non-777
airframes regardless of engine type,'' the Boeing letter sent to 777
operators last week states, according to Flight International.