Merci Beochien !
J'en profite pour mettre le lien vers le Seattle P.I. avec le commentaire de J.WALLACE ( en anglais ) :
By JAMES WALLACE
P-I AEROSPACE REPORTER
In the 13 years since The Boeing Co.'s 777 entered airline service, the plane with the most powerful commercial jetliner engines ever made has never had a fatal crash.
But in less than a year, two episodes involving Rolls-Royce engines on the 777 are giving air safety investigators cause for concern.
In January, a British Airways 777 crash-landed short of the runway to London's Heathrow Airport when the autopilot tried to apply power and both engines failed to respond. Several passengers were injured, but none seriously.Now a second 777 has experienced a similar problem with one of its two Rolls-Royce engines, the National Transportation Safety Board said Thursday.
Investigators still don't know for certain why the engines failed on the British Airways jet, although ice blocking the fuel flow is thought to have been responsible
. If that's what happened, the evidence literally melted away when the plane crashed. And that makes the latest episode even more troublesome as investigators search for clues.
This time, there was no crash. The safety board said a Delta Air Lines 777-200ER, the same model that crashed at Heathrow, was en route Nov. 26 from Shanghai, China, to Atlanta when its right engine lost thrust while the plane was cruising at 39,000 feet over Montana.
Both 777s were powered by Rolls-Royce Trent 895 engines.....
On the Delta flight, the pilots followed flight manual procedures and descended to 31,000 feet, where the engine recovered and responded normally, the safety board said. The flight, with 15 crew members and 232 passengers, continued to Atlanta, where it landed without further problem.
Flight data recorders and other data and components were retrieved from the airplane for testing and evaluation and both pilots were interviewed.The safety board noted the apparent similarities with the British Airways event.
In both cases, there was an uncommanded rollback of engine thrust.
Bill English, a senior air safety investigator with the NTSB who served as the board's representative in the Heathrow crash, is in charge of the Delta Air Lines investigation.
Britain's Air Accidents Investigation Branch, which has assigned a representative to the Delta episode, is working closely with the NTSB "to determine if there are issues common to both events," the safety board said.Boeing and Rolls-Royce are assisting in the Delta investigation and referred questions to the NTSB.
It was 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.
They determined that the 777, during the flight from China, experienced unusually cold outside air temperatures during cruise altitude. Investigators concluded that ice had apparently formed during the flight and restricted the flow of fuel to the engines.Boeing, working with European and U.S. regulators, agreed on several interim measures for Rolls-Royce-powered 777s to reduce the risks of ice causing an engine rollback.
One of those procedures calls 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 minus 10 degrees Celsius.
The General Electric engines on the 777 have a different fuel system architecture, and Boeing and GE have said the measures adopted after the Heathrow crash need apply only to 777s with the Rolls-Royce Trent engines.
But the British Air Accidents Investigation Branch, in its interim report, noted that testing of this "hitherto unknown phenomenon" has only been conducted on 777s with the Trent engines."It is unknown whether other aircraft and engine types may also be susceptible," the safety agency said.http://seattlepi.nwsource.com/business/392817_boeingengine19.html