BA38 et DL18

Vector a écrit:Dans un réchauffeur carbu, la dépression de l'air et la vaporisation du carburant créent un refroidissement intense. La dépression est d'autant plus grande que le papillon est plus fermé au ralenti et il se forme un bouchon de glace dans le venturi, ce qui bloque le passage de l'air. On ne parle quand même pas des mêmes températures. Par contre voler au ralenti dans les nuages, c'est chercher les problèmes.

alain57 a écrit: .....
dans le cas nous concernant, la glace, trouve uniquement son origine dans le carburant avant le moteur, car sur un réacteur on injecte le carburant directement dans la chambre de combustion, le carburant n'est jamais en contact avec l'air d'admission froid comme sur un moteur a carburateur. (avion, vehicule, etc) donc le point froid doit se situé dans la tuyauterie d'ammené du fuel, car je ne vois pas la glace issue du reservoir a l'état solide passer a travers les pompes situé dans les reservoirs .....les pompes qui ont cavités, sont ceux des moteurs, par manque de carburant, du a une obstruction de l'alimentation en fuel.

NTSB wants 777 engine redesigned
The National Transportation Safety Board issued an urgent safety warning Wednesday for Boeing 777s powered by Rolls-Royce engines because two of the big jets lost power during flights. One crashed while landing at London's Heathrow Airport.

Some 228 of the twin-engine jets, which can carry upwards of 350 passengers, are in service with airlines around the world.

"With two of these rollback events (losing engine thrust) occurring within a year, we believe that there is a high probability of something similar happening again," said NTSB Acting Chairman Mark Rosenker.

The safety board, which can only make recommendations, wants the Rolls-Royce engine redesigned. The Federal Aviation Administration, which would have to order any redesign, said late in the day that it had only just received the NTSB letter and had not yet had time to study the board's recommendations.

But Laura Brown, an FAA spokeswoman, noted that the agency recently issued an air-worthiness directive requiring operators of 777s with Rolls-Royce engines to take certain steps to lessen the likelihood that an engine might lose power in flight.

Any redesign and recertification of an airplane engine would be a lengthy process should the FAA decide to move forward on the safety board's recommendations, she said.

The safety board, in a statement, noted that on Feb. 23 Rolls-Royce indicated that a redesign of the engine was under way, and that the engine maker anticipated the redesign to be tested, certified and ready for installation within 12 months.

The problem has been traced to ice clogging the engine fuel lines.

Procedures developed by Boeing and the FAA to reduce the risk that the Rolls-Royce 777 engines might lose power under certain unusually cold conditions at cruise altitude are not sufficient, the board said.

"While the procedures may reduce the risk of a rollback in one or both engines… they add complexity to flight crew operations, and the level of risk reduction is not well established,'' the board said. "And because the recovery procedure requires a descent, the aircraft may be exposed to other risks such as rising terrain or hazardous weather, or the inability to achieve maximum thrust during a critical phase of flight, such as during a missed approach. Because of these hazards, the safety board has determined that the only acceptable solution to this safety vulnerability is a redesigned (engine) …''

The first 777 incident occurred in January 2008. The British Airways 777-200ER, with 152 passengers and crew members, was approaching Heathrow after a flight from Beijing when both engines failed to respond to autopilot commands for thrust. The plane crash-landed short of the runway. Several passengers were injured, but none seriously.

It turned into one of the most puzzling aviation accidents in modern times. The plane was badly damaged but 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.

Safety experts eventually determined that the British Airways jet had flown through unusually cold weather at cruise altitude and ice apparently formed in part of the engine and blocked the fuel flow.

Then another incident occurred in November when a Delta Air Lines 777-200 lost thrust in one of its Rolls-Royce engines during cruise flight over Montana while en route from Shanghai to Atlanta. The flight crew followed Boeing's published procedure and the engine was restarted. The plane landed safely in Atlanta.

In both cases, investigators determined there was a build up of ice, from water normally present in all jet fuel, on the fuel-oil heat exchanger and this restricted the flow of fuel, resulting in the engine losing power.

Boeing engineers, working in the laboratory, determined 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.

General Electric and Pratt & Whitney also make engines for the 777, but those have a different design from 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 powered only with GE engines.

In September, the FAA 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. 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 Boeing recommended, and the FAA ordered, 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 were modified by Boeing after 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.

And 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.

Earlier this month the FAA, as it did in September, issued the new air worthiness directive that made Boeing's latest recommendations mandatory. The directive affects 56 planes operated in the U.S. fleet and 228 worldwide, according to the FAA.

In its letter to the FAA, the safety board recommended that after the engine redesign is completed, the new system be installed on all affected Boeing 777s at the next maintenance check or within six months.

More than 700 Boeing 777s are in service with airlines around the world. The 777 has never had a fatal crash since it entered service with United Airlines in 1995.

FOR IMMEDIATE RELEASE: March 11, 2009 SB-09-11

NTSB ISSUES URGENT SAFETY RECOMMENDATION TO ADDRESS ENGINE THRUST ROLLBACK EVENTS ON B-777 AIRCRAFT


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Washington, DC - Following two engine thrust rollback events on Boeing 777 aircraft powered by Rolls-Royce engines, the National Transportation Safety Board issued an urgent safety recommendation today calling for the redesign of a Rolls- Royce engine component. The Safety Board also recommended that, after the redesign is completed, the new system be installed on all affected B-777 airplanes at the next maintenance check or within six months.

These recommendations are being issued in response to the findings in two investigations - an accident and an incident - involving engine thrust rollbacks on Boeing 777-200ER airplanes powered by Rolls-Royce RB211 Trent 800 Series engines. In both cases a build-up of ice (from water normally present in all jet fuel) on the fuel/oil heat exchanger (FOHE) restricted the flow of fuel to the engine, resulting in an uncommanded engine rollback.

The first event, which is still being investigated by the UK's Air Accidents Investigation Branch (AAIB), occurred on January 17, 2008, when a Boeing 777 experienced a dual engine rollback on final approach and crashed short of the runway at London's Heathrow International Airport. One passenger was seriously injured, eight passengers and four of the flight crew sustained minor injuries; the airplane was substantially damaged.

The second event occurred on November 26, 2008, when a Delta Air Lines Boeing 777 experienced a single engine rollback during cruise flight over Montana while en route from Shanghai to Atlanta. Normal operations resumed after the flight crew followed Boeing's published procedure to recover engine performance; the airplane landed safely in Atlanta.

Testing in support of the UK accident investigation led Boeing to develop procedures to help prevent ice accumulation, and to recover thrust in cases of ice blockage. As more information from the Delta rollback event was developed, Boeing modified the procedures, which became the basis of an airworthiness directive issued by the Federal Aviation Administration.

While the procedures may reduce the risk of a rollback in one or both engines due to FOHE ice blockage, they add complexity to flight crew operations, and the level of risk reduction is not well established. And because the recovery procedure requires a descent, the aircraft may be exposed to other risks such as rising terrain or hazardous weather, or the inability to achieve maximum thrust during a critical phase of flight, such as during a missed approach.

Because of these hazards, the Safety Board has determined that the only acceptable solution to this safety vulnerability is a redesigned FOHE that would eliminate the potential of ice build-up. On February 23, 2009, Rolls-Royce indicated that a redesign of the FOHE was underway, and that they anticipated the redesign to be tested, certified and ready for installation within 12 months.
"With two of these rollback events occurring within a year, we believe that there is a high probability of something similar happening again," said NTSB Acting Chairman Mark V. Rosenker. "We are encouraged to see that Rolls-Royce is already working on a redesign, and we are confident that with the FAA and EASA (European Aviation Safety Agency) overseeing the process, this flight safety issue - even one as complex as this - will be successfully and expeditiously resolved."

The NTSB has made the following two recommendations to both the Federal Aviation Administration and the European Aviation Safety Agency:

Require that Rolls-Royce redesign the RB211 Trent 800 series engine fuel/oil heat exchanger (FOHE) such that ice accumulation on the face of the FOHE will not restrict fuel flow to the extent that the ability to achieve commanded thrust is reduced.
Once the fuel/oil heat exchanger (FOHE) is redesigned and approved by certification authorities, require that operators of Boeing 777-200 airplanes powered by Rolls Royce RB211 Trent 800 series engines install the redesigned FOHE at the next scheduled maintenance opportunity or within 6 months after the revised FOHE design has been certificated, whichever comes first.

"With two of these rollback events (losing engine thrust) occurring within a year, we believe that there is a high probability of something similar happening again," said NTSB Acting Chairman Mark Rosenker.

The safety board, which can only make recommendations, wants the Rolls-Royce engine redesigned.

The Federal Aviation Administration, which would have to order any redesign, said late in the day that it had only just received the NTSB letter and had not yet had time to study the board's recommendations.

But Laura Brown, an FAA spokeswoman, noted that the agency recently issued an air-worthiness directive requiring operators of 777s with Rolls-Royce engines to take certain steps to lessen the likelihood that an engine might lose power in flight.

Any redesign and recertification of an airplane engine would be a lengthy process should the FAA decide to move forward on the safety board's recommendations, she said.

The safety board, in a statement, noted that on Feb. 23 Rolls-Royce indicated that a redesign of the engine was under way, and that the engine maker anticipated the redesign to be tested, certified and ready for installation within 12 months.

Beochien a écrit: De Sévrien !

(v) Aussi, cela donne le temps de poursuivre les investigations sur la "root-cause" (car un défaut de FOHE n'est pas et ne saurait être la "root cause").

Affirmation bien précaire, tout va exactement dans l'autre sens pour l'instant ... bon c'est noté !

Beochien a écrit: Mais la Root Cause, (Si elle existe et si ce n'est pas une combinaison inextricable de phénomènes) pourrait bien être le même FOHE !
Même si intellectuellement ça dérange !

Beochien a écrit: Reste à voir le vrai crédit et le contexte de cette thése (Ligne du rapport) AAIB .... pas forcément aussi affirmée certaine et solide ... que ce veut nous faire croire M Sévrien !

Beochien a écrit: Thése qui fond visiblement assez vite, presque comme glace au soleil, pourrait on dire !
1 ligne donc qui à fait remplir 50 pages et qui est de moins en moins probable ... bon ... il n'y a plus que Sévrien qui s'accroche à ce fil (Bouée) bien ténu ...
L'ice Build up dans le réservoir semble de plus en plus improbable ...
Et aucune mesure n'est prise dans ce sens ! Visiblement plus personne ne considére sérieusement cette possibilité !

Beochien a écrit:De Sévrien !

(v) Aussi, cela donne le temps de poursuivre les investigations sur la "root-cause" (car un défaut de FOHE n'est pas et ne saurait être la "root cause").

Affirmation bien précaire, tout va exactement dans l'autre sens pour l'instant ... bon c'est noté !

Mais la Root Cause, (Si elle existe et si ce n'est pas une combinaison inextricable de phénomènes) pourrait bien être le même FOHE !
Même si intellectuellement ça dérange !
-----------------------------------------------

While the procedures may reduce the risk of a rollback in one or both engines due to FOHE ice blockage, they add complexity to flight crew operations, and the level of risk reduction is not well established. And because the recovery procedure requires a descent, the aircraft may be exposed to other risks such as rising terrain or hazardous weather, or the inability to achieve maximum thrust during a critical phase of flight, such as during a missed approach.

Because of these hazards, the Safety Board has determined that the only acceptable solution to this safety vulnerability is a redesigned FOHE that would eliminate the potential of ice build-up. On February 23, 2009, Rolls-Royce indicated that a redesign of the FOHE was underway, and that they anticipated the redesign to be tested, certified and ready for installation within 12 months.

"With two of these rollback events occurring within a year, we believe that there is a high probability of something similar happening again," said NTSB Acting Chairman Mark V. Rosenker. "We are encouraged to see that Rolls-Royce is already working on a redesign, and we are confident that with the FAA and EASA (European Aviation Safety Agency) overseeing the process, this flight safety issue - even one as complex as this - will be successfully and expeditiously resolved."

The NTSB has made the following two recommendations to both the Federal Aviation Administration and the European Aviation Safety Agency:

Require that Rolls-Royce redesign the RB211 Trent 800 series engine fuel/oil heat exchanger (FOHE) such that ice accumulation on the face of the FOHE will not restrict fuel flow to the extent that the ability to achieve commanded thrust is reduced.
Once the fuel/oil heat exchanger (FOHE) is redesigned and approved by certification authorities, require that operators of Boeing 777-200 airplanes powered by Rolls Royce RB211 Trent 800 series engines install the redesigned FOHE at the next scheduled maintenance opportunity or within 6 months after the revised FOHE design has been certificated, whichever comes first.

Because of these hazards, the Safety Board has determined that the only acceptable solution to this safety vulnerability is a redesigned FOHE that would eliminate the potential of ice build-up. On February 23, 2009, Rolls-Royce indicated that a redesign of the FOHE was underway, and that they anticipated the redesign to be tested, certified and ready for installation within 12 months.