Airfoilmod
Entirely agree with your last post.
If the FOHE has ice in the Fuel passages, care must be taken to avoid a sudden increase that disturbs the ice upstream, allowing it to drop and block completely the exit of the Fuel passage from the FOHE. If I read it right, the proposed RR interim fix addresses tube protrusion from the tubesheet, effectively making it smoother with less places for ice to catch and build up. Sooty |
Solution
Perhaps demoting the FOHE to a secondary system, an ancillary instead of a singular, and Flight Critical component. If I was to propose a fix:
Build a new, shorter HE that has a "Y" at either end, allowing the provision of a gate valve that can Divert Fuel AROUND the Cannister to a Flow Only Bypass that supplies the HP directly in Cold Cruise. If the HE is Bench Built and conforms to existing Entry Exit Plumbing, It could be fitted in a scheduled C or D break, for uninterrupted revenue and Plumbing redesign. I'll call my patent Atty. Interested? AF |
Solution to wrong problem, perhaps
Stopping the ice build-up in the FOHE is IMHO addressing the symptoms, not the disease. If there is sufficient incipient ice in the fuel flow, when the holes in the cheese line up it will find somewhere to accumulate.
Wouldn't it be better to stop the ice at source, or at least stop it being released into the engine? Sooty |
Incurable
The Problem isn't Ice, it's water. "In Spec." Fuel has it and at very low temps it takes shape as granular microscopic particles. As such, it does no harm. At Cruise, in VERY low temp. over many hours, the ice melts and refreezes in the FOHE. It can reaccumulate at the small bore exits to the HP's., cause cavitation and starvation, as discussed. Heating, melting at the entry and immediately refreezing downstream is the problem. Oil cooling is not necessary at this point, indeed, the Oil (mostly) bypasses the FOHE anyway., so why direct the Fuel through a periodically unnecessary Path?
The solution isn't water free Fuel, which is impossible anyway; but directing Fuel around vulnerability in the Fuel Path when it may create problems. AF |
SOOTY "Stopping the ice build-up in the FOHE is IMHO addressing the symptoms, not the disease. If there is sufficient incipient ice in the fuel flow, when the holes in the cheese line up it will find somewhere to accumulate" KEEL BEAM From 6th Sept 2008 "I am surprised this has not been more in the forefront of thoughts. I cannot say specifically for the B747SP, but certainly for the "classic" B747 and going back a few more years, the B707, they had dedicated fuel heaters. these were switched on by the flight engineer if he had a Fuel Filter Block warning light. After a set period of time, the fuel heater was switched off. Looking at the diagrams on this thread, fuel heating is only supplied by the Fuel/Oil heat exchanger. Just a thought ...." How much money would need to be spent on having fuel that does not hold water and to have some sort of system on the fuel tanks to prevent water ingress through condensation etc.? The Fuel Heater would be a simpler solution to the accumulation of ice. Now the argument would be, where do you place the Fuel Heater, on the engine? At the front spar? In the tank? (I would go for the engine!) |
(Non-pilot speaking)
But if you placed it in the engine - you have to pump the fuel there first ...? My uneducated guess as to why fuel heaters were discontinued would be: 1) We have better fuel spec these days 2) We can save the weight and cost of these units Followed by:- 3) It's worked well since we stopped installing fuel heaters ... Humans usually have to learn things more than once. |
Quick question and please excuse me for not going thru 115 pages to see it was already brought up:
Does the B777 have a fuel recirculating system to warm the stored fuel? My current bizjet does by recirc'ing fuel out of the oil cooler directly back into the wing tanks. GF |
Paxboy My uneducated guess as to why fuel heaters were discontinued would be: 1) We have better fuel spec these days 2) We can save the weight and cost of these units Followed by:- 3) It's worked well since we stopped installing fuel heaters ... |
Heat Recovery
And don't forget that the energy to heat the fuel is paid for in increased fuel burn. Only a small proportion of that comes back in the efficiency gain of hotter fuel for combustion |
N T S B Issues Urgent Safety Recommendation To Address Engine Thrust Rollback Events
************************************************************
NTSB PRESS RELEASE ************************************************************ National Transportation Safety Board Washington, DC 20594 FOR IMMEDIATE RELEASE: March 11, 2009 SB-09-11 ************************************************************ NTSB ISSUES URGENT SAFETY RECOMMENDATION TO ADDRESS ENGINE THRUST ROLLBACK EVENTS ON B-777 AIRCRAFT ************************************************************ 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. The NTSB and AAIB will continue to work together closely on both of the rollback events as each of the investigations move forward. Safety recommendation letter to the Federal Aviation Administration: http://ntsb.gov/Recs/letters/2009/A09_17_18.pdf Safety recommendation letter to the European Aviation Safety Agency: http://ntsb.gov/Recs/letters/2009/A09_19_20.pdf Image: Ice accumulation on the inlet face of a Rolls-Royce RB211 Trent 800 Series Fuel/Oil Heat Exchanger during testing >>> http://www.ntsb.gov/Pressrel/2009/FOHEface.jpg ### NTSB Media Contact: Peter Knudson (202) 314-6100 [email protected] ************************************************************ |
NTSB Safety Recommendation
It's hard to imagine that the NTSB has sufficient data and risk assessment expertise to step in front of the public and say that the currently issued AD and incorporation schedule would not adequately minimize the risk.
It sounds more like a "me too" and I'm in charge. |
NTSB
Is a BOARD. FAA is an AUTHORITY. The NTSB has forced FAA's hand. This isn't "me too", this is: "get busy". I think FAA determination will follow. Since the First mitigation didn't work (the "non-normal" one) there is great risk in merely "guessing" at a replacement, and NTSB has said it isn't acceptable anyway. The FAA diverges at great risk. The affected A/C I think will soon be parked. The NTSB's Move will temper the flack the grounding will engender, but those who complain will be criticized roundly. As I see it, it is appropriate for the Investigative Body (NTSB) to make findings of fact, then pass their work along to the rule making authority to direct a response by rule making. (FAA'S) job.
AF |
Further reading
Of Ms. Osmus' letter reveals an opening left for the FAA. The NTSB anticipates a refit around maintenance schedules. This allows the FAA to come down authoritatively in ordering a fleet park.
There is some astonishing indictment of the as built FOHE as well. There are vast legal issues here, to put it mildly. AF |
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. ....more than 60 years ago without CADM and with bombs dropping on one's offices and factories ! |
Harry
I think from first order to first flight was 15 months for the Mustang? I'll check that. Check That, make it 117 DAYS.
AF |
Image: Ice accumulation on the inlet face of a Rolls-Royce RB211 Trent 800 Series F
|
Now THAT'S an occluded artery.
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It's nice to see the NTSB and FAA agree with my guess from the 16th Feb 08!!
I've a good mind to name the ***** who questioned my basic understanding of aircraft systems when I put forward the idea of cold soaked system causing a restriction though the FCOC. I know it's correctly called a FOHE but I'm a bit stuck in my ways. Where do I claim my prize? Sorry for the cell phone interference brigade. You guys were banking on this weren't you? :-) |
C N N Article Regarding The Above N T S B Recommendation
WASHINGTON (CNN) -- Federal transportation safety officials Wednesday issued an "urgent" recommendation calling for a redesign of a component on some Boeing 777 aircraft engines -- a component blamed for two major mishaps in the past year.
Authorities have called for the redesign of an engine part in some Boeing 777s. National Transportation Safety Board investigators said the Rolls-Royce engine component played a role in the January 17, 2008, crash of a British Airways jet near London's Heathrow Airport. Both the plane's engines lost power as the plane approached the runway, and 13 people were injured in the resulting crash. Ten months later, on November 26, 2008, a Delta Air Lines Boeing 777 was in cruise flight over Montana when an engine lost power. That plane landed safely in Atlanta after pilots performed a procedure developed in response to the Heathrow crash. In both cases, the NTSB said, a build-up of ice on a fuel/oil heat exchanger restricted the flow of fuel to the Rolls-Royce engines, reducing power. "With two of these rollback events occurring within a year, we believe that there is a high probability of something similar happening again," NTSB Acting Chairman Mark Rosenker said in a news release. The Federal Aviation Administration recently ordered operators of affected Boeing 777s to revise flight manuals to give pilots procedures to follow in certain cold weather conditions, outlining steps they should take if their jets experience a reduction of power. But the NTSB said Wednesday the FAA action does not go far enough. "The procedure has worked and it has been effective in significantly reducing the likelihood [of an incident]," said NTSB spokesman Peter Knudson. "But that's not enough. We need a permanent fix." While the emergency procedures work, they add to the complexity of flying the plane and require a descent, which could be hazardous if the plane is not at a sufficient altitude, the NTSB said. Some 56 aircraft in the U.S. fleet and a total of 228 worldwide are equipped with Rolls-Royce engines. But the NTSB stopped short of recommending the planes be grounded. Knudson said the safety board believes the new procedures will significantly address the problem until Rolls-Royce has a new component ready for installation. Rolls-Royce indicated it can have a new system ready within 12 months, the NTSB said. "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," Rosenker said. The NTSB recommended that, once Rolls-Royce completes its redesign, the new system be installed on all affected Boeing 777's at their next maintenance check or within six months. No one from Rolls-Royce was immediately available for comment. "This is a serious matter for those airlines operating the 777 with Rolls-Royce engines," said Richard Quest, CNN's aviation correspondent . "There is a satisfactory temporary solution, but a long-term fix is what the NTSB is demanding." |
"There is a satisfactory temporary solution..."
In school, "satisfactory" rates a grade of "C". Quest isn't much more optimistic than Rosenker or Knudson. I still think the NTSB, in not calling for "a grounding" has simply left the door open for their counterpart (FAA) to do so.
AF |
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