BA038 (B777) Thread
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Cheeses
The latest advisory has deflected thinking on this thread into the mechanics of the Trent powerplant. But in reality its another cheese situation all over again, and the three relevant Cheeses are: temperature profile, fuel quality, and powerplant design. Only two of these, realistically/sensibly, can we change.
FE Hoppy and I, and one or two others way back at the beginning of 2008 said that the fuel will have had a role, and in the last few days Airfoil Mod and Spilko have reiterated that thought.
Blocking at least one hole in the cheese (Trent 800 FOHE redesign) takes care of the issue at least on the surface. But I would be more comfortable if someone could compare the performance with the current Trent powerplant flying the same temperature profile with fuels from from, say a European or a US refinery, compared to RP-3. (Jet Fuel #3, even when on spec and meeting Jet A-1 spec, can sometimes be, like Russian fuel, different compositionally to 'traditional' Jet A/A-1, if there can be said to be such a thing).
There was a statement in this thread some time ago referring to the fact that the behaviour of Jet fuel under extreme low temperature conditions was being shown to throw up some surprises in the testing following the incident, indicating that our knowledge may not be as good as we thought. Well, yes. I have said in an earlier thread why the recovered fuel may not be fully representative of the loaded fuel and in the final report I would like to see the GC/MS curves of the retention sample vs the recovered sample as well as the usual tests that define on-spec Jet fuel so we can have an educated guess at understanding the role that the fuel played - or not.
One thing I dont understand is a constant lack of reference to the retention sample. The AAIB report says that "It was estimated that the fuel uplifted in Beijing at the start of the accident flight might have contained up to 70 ppm of dissolved and entrained (suspended) water". Why estimate? Use the value that was in the retention sample which you will have analysed... or do you not actually have a valid retention sample?"
But, more generally, why should we bother? Surely if we block one cheese hole by fixing the Trent issue we can pack up and go home because the issue is fixed whether there is loads of water in the fuel or not?
The answer is we should bother because over the next five years we will see a proliferation in biofuel-based and Gas-to-liquids (GTL) based Jet A/A-1 blends some of which have known issues related to low temperature performance. The kinds of research that is now being conducted following the BA 038 incident is badly needed to ensure we can reliably predict performance and compatibility issues with, and better testing for, drop-in biojet blends which will prevent a similar incident. We need to confirm that the current testing regime - which has been in place with only a few modifications since before most of us were born - is sufficiently protective in current operational situations and with the diverse range of fuels that are about to enter the mainstream.
Can we afford not to block the second hole in the cheese by fully understanding the role that fuel played in the incident and the implications for different fuels that will be with us within a decade? That is why we must fully support the establishment of a joint FAA-EASA research and testing program that is a recommendation of Interim report 2.
Pinkman
FE Hoppy and I, and one or two others way back at the beginning of 2008 said that the fuel will have had a role, and in the last few days Airfoil Mod and Spilko have reiterated that thought.
Blocking at least one hole in the cheese (Trent 800 FOHE redesign) takes care of the issue at least on the surface. But I would be more comfortable if someone could compare the performance with the current Trent powerplant flying the same temperature profile with fuels from from, say a European or a US refinery, compared to RP-3. (Jet Fuel #3, even when on spec and meeting Jet A-1 spec, can sometimes be, like Russian fuel, different compositionally to 'traditional' Jet A/A-1, if there can be said to be such a thing).
There was a statement in this thread some time ago referring to the fact that the behaviour of Jet fuel under extreme low temperature conditions was being shown to throw up some surprises in the testing following the incident, indicating that our knowledge may not be as good as we thought. Well, yes. I have said in an earlier thread why the recovered fuel may not be fully representative of the loaded fuel and in the final report I would like to see the GC/MS curves of the retention sample vs the recovered sample as well as the usual tests that define on-spec Jet fuel so we can have an educated guess at understanding the role that the fuel played - or not.
One thing I dont understand is a constant lack of reference to the retention sample. The AAIB report says that "It was estimated that the fuel uplifted in Beijing at the start of the accident flight might have contained up to 70 ppm of dissolved and entrained (suspended) water". Why estimate? Use the value that was in the retention sample which you will have analysed... or do you not actually have a valid retention sample?"
But, more generally, why should we bother? Surely if we block one cheese hole by fixing the Trent issue we can pack up and go home because the issue is fixed whether there is loads of water in the fuel or not?
The answer is we should bother because over the next five years we will see a proliferation in biofuel-based and Gas-to-liquids (GTL) based Jet A/A-1 blends some of which have known issues related to low temperature performance. The kinds of research that is now being conducted following the BA 038 incident is badly needed to ensure we can reliably predict performance and compatibility issues with, and better testing for, drop-in biojet blends which will prevent a similar incident. We need to confirm that the current testing regime - which has been in place with only a few modifications since before most of us were born - is sufficiently protective in current operational situations and with the diverse range of fuels that are about to enter the mainstream.
Can we afford not to block the second hole in the cheese by fully understanding the role that fuel played in the incident and the implications for different fuels that will be with us within a decade? That is why we must fully support the establishment of a joint FAA-EASA research and testing program that is a recommendation of Interim report 2.
Pinkman
Last edited by Pinkman; 15th Mar 2009 at 00:24.
Keeping Danny in Sandwiches
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There is a very real difference between twins and quads and that is the surplus of power available on twins which together with efficient wing design allows higher cruise altitudes than quads and with it lower temperatures.
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With respect, it's in here. Happy reading.
Further:
Be careful of "Fuel Heating". It is warmer temps that created the hazard, not "very cold" Fuel. (Though it was a precursor).
Location of FOHE? perhaps away from the Fan Shroud a bit.
Bypass, a no brainer. Though GE uses the concept to further cool the oil, in this case, a "recirculation" not strictly a "bypass".
The Bottom Line? The Fuel system as a whole on this combination wants to be a bit more complex, to include additional mitigating procedures and mechanicals. It always looked a little simplistic, turns out it is.
vapilot -It is always hazardous to rely on the unknown, or statistics. If what you mean is "one in one hundred thousand" of an additional occurence, think about how many months it takes the Fleet to hit 50,000 trips. At that point the chance? ONE in TWO. Let's see, 228 a/c, one trip a day, 1,000 every 4 days, twenty thousand every 80 days (Five to One), etc. See?
Further:
Be careful of "Fuel Heating". It is warmer temps that created the hazard, not "very cold" Fuel. (Though it was a precursor).
Location of FOHE? perhaps away from the Fan Shroud a bit.
Bypass, a no brainer. Though GE uses the concept to further cool the oil, in this case, a "recirculation" not strictly a "bypass".
The Bottom Line? The Fuel system as a whole on this combination wants to be a bit more complex, to include additional mitigating procedures and mechanicals. It always looked a little simplistic, turns out it is.
vapilot -It is always hazardous to rely on the unknown, or statistics. If what you mean is "one in one hundred thousand" of an additional occurence, think about how many months it takes the Fleet to hit 50,000 trips. At that point the chance? ONE in TWO. Let's see, 228 a/c, one trip a day, 1,000 every 4 days, twenty thousand every 80 days (Five to One), etc. See?
Then there are the people in a quiet room somewhere at Mega-Corp Airlines' home office that crunch such numbers regularly. Our regulators also play this game, something I find the NTSB and the FAA at 'odds' on constantly.
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Airfoilmod, yes you are correct about fuel heating, the temperature issue was addressed in the AAIB report however there is a need for fuel heating if and when the FOHE becomes blocked. An earlier suggestion in the thread drew attention to a similar problem on the DC8 that was solved by reversing the flow of oil to have the hottest oil near the inlet face.
It might be a useful addition to the OH panel to have a differential pressure light activated by sensors either side pf the FOHE, I quick cheap mod that would alert crews to a potential problem.
An alternative solution could be to have air/oilHE.
It might be a useful addition to the OH panel to have a differential pressure light activated by sensors either side pf the FOHE, I quick cheap mod that would alert crews to a potential problem.
An alternative solution could be to have air/oilHE.
Plastic PPRuNer
Unexpected ice formation in areas of restricted flow has caused problems in the past, viz. the loss of the nuclear powered attack submarine USS Thresher (SSN-593) in 1963.
"Thresher had probably suffered the failure of a join in a salt water piping system, which relied heavily on silver brazing instead of welding; earlier tests using ultrasound equipment found potential problems with about 14% of the tested brazed joints, most of which were determined not to pose a risk significant enough to require a repair. High-pressure water spraying from a broken pipe joint may have shorted out one of the many electrical panels, which in turn caused a shutdown ("scram") of the reactor, with a subsequent loss of propulsion. The inability to blow the ballast tanks was later attributed to excessive moisture in the ship's high-pressure air flasks, which froze and plugged the flasks' flowpaths while passing through the valves. This was later simulated in dock-side tests on Thresher’s sister ship, USS Tinosa (SSN-606). During a test to simulate blowing ballast at or near test depth, ice formed on strainers installed in valves; the flow of air lasted only a few seconds. Air driers were later retrofitted to the high pressure air compressors, beginning with Tinosa, to permit the emergency blow system to operate properly."
"Thresher had probably suffered the failure of a join in a salt water piping system, which relied heavily on silver brazing instead of welding; earlier tests using ultrasound equipment found potential problems with about 14% of the tested brazed joints, most of which were determined not to pose a risk significant enough to require a repair. High-pressure water spraying from a broken pipe joint may have shorted out one of the many electrical panels, which in turn caused a shutdown ("scram") of the reactor, with a subsequent loss of propulsion. The inability to blow the ballast tanks was later attributed to excessive moisture in the ship's high-pressure air flasks, which froze and plugged the flasks' flowpaths while passing through the valves. This was later simulated in dock-side tests on Thresher’s sister ship, USS Tinosa (SSN-606). During a test to simulate blowing ballast at or near test depth, ice formed on strainers installed in valves; the flow of air lasted only a few seconds. Air driers were later retrofitted to the high pressure air compressors, beginning with Tinosa, to permit the emergency blow system to operate properly."
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As people seem to be taking the NTSB press release a little bit too far, I will repeat what I wrote in post 2282 :-
======================
======================
From the NTSB press release posted above :-
"......... 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. ............" (my bold)
Fascinating.
According to this, the two investigations have been completed (at least they have specific "findings" and are factually known) as opposed to theories or speculation !
Likewise, they have supposedly explained where the additional water came to cause the problem.
Unforunately they haven't bothered to highlight other engine installations in other planes which need similar flight restrictions.
.
=====================
=====================
The AAIB interim report number 2 only indicates the possibility of the FOHE being the problem. Its experients were with fuel with 90 ppm rather than the expected maximum 70 ppm of the actual accident plane which had tested remains of 40 ppm and of which the expected maximum of 70 ppm would have been reduced by ice forming at the bottom surface of the tanks.
For the cause of the accident to be properly explained the fault must be properly explained - it is not good enough to guestimate it.
Likewise, other aircraft with various other enginge/fuel installations should be examined for possible similar problems with the new phenomomen of fuel/ice slush (or whatever they are going to call it.
People seem to think the work is over and the aviation world has the problem put to bed - there could be masses more work to come.
As for the near simultaneous fasilure in two separate systems and its effect on ETOPS I will ignore that due to total ignorance.
.
======================
======================
From the NTSB press release posted above :-
"......... 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. ............" (my bold)
Fascinating.
According to this, the two investigations have been completed (at least they have specific "findings" and are factually known) as opposed to theories or speculation !
Likewise, they have supposedly explained where the additional water came to cause the problem.
Unforunately they haven't bothered to highlight other engine installations in other planes which need similar flight restrictions.
.
=====================
=====================
The AAIB interim report number 2 only indicates the possibility of the FOHE being the problem. Its experients were with fuel with 90 ppm rather than the expected maximum 70 ppm of the actual accident plane which had tested remains of 40 ppm and of which the expected maximum of 70 ppm would have been reduced by ice forming at the bottom surface of the tanks.
For the cause of the accident to be properly explained the fault must be properly explained - it is not good enough to guestimate it.
Likewise, other aircraft with various other enginge/fuel installations should be examined for possible similar problems with the new phenomomen of fuel/ice slush (or whatever they are going to call it.
People seem to think the work is over and the aviation world has the problem put to bed - there could be masses more work to come.
As for the near simultaneous fasilure in two separate systems and its effect on ETOPS I will ignore that due to total ignorance.
.
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how to make a million.
Some one needs to come up with an inline water extractor for fuel that can be retro-fitted the aircraft fuel systems upstream of where the ice may become a problem.
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ETOPS
Phil - the concurrent rollbacks are not mysterious, neither are they complicated. Nearer the engines, the Fuel systems "rejoin" in their critical attributes. The Plumbing, Fuel, and Fuel delivery systems are virtually identical, close in. Given they burn the same Fuel, stored identically, in identical ambient temps, I think I can explain why #2 quit seven seconds before #1. The #1 engine (Port) was fed from a tank in a wing that had been in the Sun flying West. The Starboard wing tank was in the shade of the Fuselage, on the North side of the a/c.
Right or wrong, ETOPS isn't perfect. Facetiously I suggested in a post way long ago, that true isolation would be served by mounting a Trent on #1 pylon and a GE on #2. "Designed Anomalous Systems" - DAS. What Else could I call it?
What I think would be fascinating is a hard copy made available of this thread. Warts and All. Informal Hangar Talk with the odd expert poking in now and again, a year long exercise in the new format of the "Pilot Lounge"
AF
Right or wrong, ETOPS isn't perfect. Facetiously I suggested in a post way long ago, that true isolation would be served by mounting a Trent on #1 pylon and a GE on #2. "Designed Anomalous Systems" - DAS. What Else could I call it?
What I think would be fascinating is a hard copy made available of this thread. Warts and All. Informal Hangar Talk with the odd expert poking in now and again, a year long exercise in the new format of the "Pilot Lounge"
AF
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FE Hoppy
Cool the Fuel at the Refinery and filter it, removing the Ice before it gets into the a/c. You think Jet is expensive now, wow. If an a/c can separate the water in flight (Ice), I think it could be done on the ground.
"Sticky Ice" ?? Teflon Pipes.
sky9 GE "Heats the Fuel" with a second pass through the FOHE.
bernd What of the GE architecture ? (HP) in front of their FOHE instead of downstream of it?
Phil Depending on who can make the better case, "It's the Fuel", "No it's the Trent", some compromise may involve all other types. But it's a hard sell, without a record of at least an "Incident" on another non 777-200ER a/c
I also think there are folks in China hoping for another incident that doesn't involve Chinese Fuel. (Consider the foul-up outcome in China?)
Bypass, Bypass, Bypass. (Blender included, no extra charge)
AF
"Sticky Ice" ?? Teflon Pipes.
sky9 GE "Heats the Fuel" with a second pass through the FOHE.
bernd What of the GE architecture ? (HP) in front of their FOHE instead of downstream of it?
Phil Depending on who can make the better case, "It's the Fuel", "No it's the Trent", some compromise may involve all other types. But it's a hard sell, without a record of at least an "Incident" on another non 777-200ER a/c
I also think there are folks in China hoping for another incident that doesn't involve Chinese Fuel. (Consider the foul-up outcome in China?)
Bypass, Bypass, Bypass. (Blender included, no extra charge)
AF
Last edited by airfoilmod; 15th Mar 2009 at 16:53. Reason: speling
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AirFoil Mod
AirfoilMod
I told you before...stick to what you know (clearly not fuel systems)! Take the water out at the refinery (they do - there are filters and coalescers) and it will be back again by the time the fuel reaches the aircraft.
Water is removed and checked for again and again. But the nature of the fuelling supply chain and the fact that heating and cooling of fuel takes dissolved water and condenses and re-entrains it as free/suspended water means it will ALWAYS be present at low levels in aircraft tanks.
The point that I agree with you is that there are lots of other fuel related questions that havent been asked, let alone answered. Chinese Jet fuel has an incredibly low (better) freeze point than Jet (-40C) or Jet A-1 (-47C). At THAT temperature (better than - 50C) how would the GE system perform?
Pinkman
I told you before...stick to what you know (clearly not fuel systems)! Take the water out at the refinery (they do - there are filters and coalescers) and it will be back again by the time the fuel reaches the aircraft.
Water is removed and checked for again and again. But the nature of the fuelling supply chain and the fact that heating and cooling of fuel takes dissolved water and condenses and re-entrains it as free/suspended water means it will ALWAYS be present at low levels in aircraft tanks.
The point that I agree with you is that there are lots of other fuel related questions that havent been asked, let alone answered. Chinese Jet fuel has an incredibly low (better) freeze point than Jet (-40C) or Jet A-1 (-47C). At THAT temperature (better than - 50C) how would the GE system perform?
Pinkman
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Thanks for the reminder
Pinkman. What is your input on the type of Ice reported by Boeing? What about the GE architecture? Alcohol or other solutions?
I'll reel meself in if you open up a bit. Deal?
AF
One other thing before you cry Uncle at H2O in Fuel. Nitrogen transporters? Closed system pumping. May be time to build Fuels for ETOPS in water free enviros?
I'll reel meself in if you open up a bit. Deal?
AF
One other thing before you cry Uncle at H2O in Fuel. Nitrogen transporters? Closed system pumping. May be time to build Fuels for ETOPS in water free enviros?
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Apologies if this question has been asked before.
I am a very frequent non-pilot flyer, and always assumed that safety was in part my responsibility. I listen to briefings, check for exits and scan this forum from time to time for news on flight safety.
I had never felt great about flying the atlantic with twin engine planes, but had taken some comfort from ETOPS certification, understanding that the chance of failure was extremely low given the testing and modelling of systems in ETOPS certified planes.
In the face of the documented problems and NTSB warnings, how is the 777 able to maintain its ETOPS rating?
I am a very frequent non-pilot flyer, and always assumed that safety was in part my responsibility. I listen to briefings, check for exits and scan this forum from time to time for news on flight safety.
I had never felt great about flying the atlantic with twin engine planes, but had taken some comfort from ETOPS certification, understanding that the chance of failure was extremely low given the testing and modelling of systems in ETOPS certified planes.
In the face of the documented problems and NTSB warnings, how is the 777 able to maintain its ETOPS rating?
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andy
It's been asked, but perhaps not quite so well or succinctly.
First of all, it isn't 777. It is one iteration, the 777-200-ER (Extended Range). The one with the Trent RB211-800 engine fit. There are 228 of these flying.
As for your question, no one can or will say. The FAA (EASA's counterpart in America), has issued an Airworthiness Directive (AD) regarding prevention/mitigation of the problem of Ice plugging the FOHE. It is assumed that this step is sufficient to make safe this fleet of a/c for now, anticipating the development and certification of a replacement for the challenged system. When that fix is available, the a/c will be refit in some sequence deemed appropriate to the specific fleet. This is my understanding, and since an error in this forum is immediately pounced upon, I am reasonably confident of its accuracy.
AF
First of all, it isn't 777. It is one iteration, the 777-200-ER (Extended Range). The one with the Trent RB211-800 engine fit. There are 228 of these flying.
As for your question, no one can or will say. The FAA (EASA's counterpart in America), has issued an Airworthiness Directive (AD) regarding prevention/mitigation of the problem of Ice plugging the FOHE. It is assumed that this step is sufficient to make safe this fleet of a/c for now, anticipating the development and certification of a replacement for the challenged system. When that fix is available, the a/c will be refit in some sequence deemed appropriate to the specific fleet. This is my understanding, and since an error in this forum is immediately pounced upon, I am reasonably confident of its accuracy.
AF
Last edited by airfoilmod; 16th Mar 2009 at 15:32.
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Statistics
airfoilmod says in #2341:
The statistics just don't mean that. The implication is that on analysis of several million trips (or tens of millions - I don't have my statistics textbooks to hand and my maths degree is getting a little rusty) it will turn out that the event will have occurred in about one in a hundred thousand. The statistic does not mean that there will definitely be one occurrence, and only one occurrence, in every sample of 100,000 trips. Without presence of a common causal factor, any two trips are equally likely (or unlikely) to hit the problem.
It is always hazardous to rely on the unknown, or statistics. If what you mean is "one in one hundred thousand" of an additional occurence, think about how many months it takes the Fleet to hit 50,000 trips. At that point the chance? ONE in TWO. Let's see, 228 a/c, one trip a day, 1,000 every 4 days, twenty thousand every 80 days (Five to One), etc. See?
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Dairyground
Noted. In my job long ago as a croupier, I was taught that each roll of the dice is independent of all others. Without drifting into chaos theory, or Quanta, the odds on rolling a seven are six in thirty six. I once saw eleven straight passes at the table, the "odds" are very long. Would you place a wager on such a thing. For a pax, the odds are almost nil that a rollback will occur. A frequent pax not so nil. Pilots less so, the Carrier has the most exposure of all, except the Authority has all of it.
AF
Please note I said NOT to rely on statistics. And include the Flip of your assertion to wit: It may happen more often than one in 100,000. That it happened once is startling (look at the length of this thread), twice is astonishing, absent your "Common Cause".
No less an authority than NTSB claims a recurrence is "likely". Read the report..... Less Faeries on a pin, more on the conclusion of the lab coats.
AF
Please note I said NOT to rely on statistics. And include the Flip of your assertion to wit: It may happen more often than one in 100,000. That it happened once is startling (look at the length of this thread), twice is astonishing, absent your "Common Cause".
No less an authority than NTSB claims a recurrence is "likely". Read the report..... Less Faeries on a pin, more on the conclusion of the lab coats.
In the face of the documented problems and NTSB warnings, how is the 777 able to maintain its ETOPS rating?
EROPs includes all engine combinations including Quads and dependent failures like ice
I'm far more concerned abot fleet statistics impacting EROPs than ETOPs
but I'll leave that to the statiticians to ponder
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Chinese Jet fuel has an incredibly low (better) freeze point than Jet (-40C) or Jet A-1 (-47C). At THAT temperature (better than - 50C) how would the GE system perform?
During the NTSB testing, they discovered that ice is stickier and more troublesome not at the lowest fuel operating temps, but in the bottom third of the typical range for the flight profile. The lower freeze formulation of that particular fuel moved the range into the area of concern.
I remain perplexed as to how this was missed during the airframe fuel system & engine certification and design paths and why the problem has remained hidden until now.
One other thing before you cry Uncle at H2O in Fuel. Nitrogen transporters? Closed system pumping. May be time to build Fuels for ETOPS in water free enviros?
Last edited by Dont Hang Up; 15th Mar 2009 at 22:29. Reason: typos