BA038 (B777) Thread
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FOHE
A lot of surface area in a "small" volume. It fits previous conjecture. The design of the exchanger resembles a "filter", though not its intended purpose, other than as a heat sink; accumulations of small crystalline ice as suggested by Captain Cargill, to be "melted" by thrust augment sounds reasonable.
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Regarding the melting of ice by the FOHE, it has been pointed out on this thread that sometimes hot oil is circulating, sometimes not as is required.
This must throw another spanner in the works, surely?
This must throw another spanner in the works, surely?
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Purpose
I think the purpose of the Fuel/Oil Heat exchanger is to cool the engine oil with fuel on its way to the combustors. The spanner is the melting of water ice built up in the passages of the unit which then is injected and possibly quenches/prevents combustion.
The unit can be cooler than is planned for when long periods of exposure to high altitude temps and little power demand keep the oil cool and allows for ice build up in the HE. What hasn't been addressed adequately imho is the presence of water in the fuel. Unless we buy the explanation about some new and unpredicted science re: FUEL at low temp. (sic). Another possibility is the melting and REFREEZING of water, which then inhibits fuel flow to the engine. Relative difference in EPR ?
The unit can be cooler than is planned for when long periods of exposure to high altitude temps and little power demand keep the oil cool and allows for ice build up in the HE. What hasn't been addressed adequately imho is the presence of water in the fuel. Unless we buy the explanation about some new and unpredicted science re: FUEL at low temp. (sic). Another possibility is the melting and REFREEZING of water, which then inhibits fuel flow to the engine. Relative difference in EPR ?
Last edited by airfoilmod; 2nd Feb 2009 at 20:13.
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It is possible however unlikely that the hot oil/no hot oil in the heat exchanger, could be the very last hole in the swiss cheese?
I think there would have to be more than 5 liters of water to do it though.
I try to keep off this part of the forum, but I just couldn't resist my two penny worth!
I think there would have to be more than 5 liters of water to do it though.
I try to keep off this part of the forum, but I just couldn't resist my two penny worth!
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Airfoilmod:
Correct.
Wouldn't lead to cavitation. Perhaps the spanner is a mix: release of ice build-up in and/or before FOHE causes obstruction.
Quite likely. And its position vs that of other powerplant mfg's.
As in the tested samples from BA038, or fuel in general?
I think the purpose of the Fuel/Oil Heat exchanger is to cool the engine oil with fuel on its way to the combustors.
The spanner is the melting of water ice built up in the passages of the unit which then is injected and possibly quenches/prevents combustion.
The unit can be cooler than is planned for when long periods of exposure to high altitude temps and little power demand keep the oil cool and allows for ice build up in the HE.
What hasn't been addressed adequately imho is the presence of water in the fuel.
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Machaca
What could cause cavitation quite easily is a melting and Refreezing of ice crystals seriously necking down the flow, or even temporarily cutting it off completely.
Fuel in general: Storage, transport, transfer, etc.
BA038: sumping negligence, lack of critical procedure compliance
(Would apply to other carriers of course.)
There seems to be an unwillingness to address wet fuel other than spec measurement and an eagerness to eliminate contaminated supplies. Instead, the drill is "Undiscovered fuel characteristics, etc." at very low temp...
The Trent has an exposure here, vis a vis FOHE and other plumbing.
A very small amount of ice, perhaps present in barely nucleated crystals, could deposit over time in restricted flow areas. In other words, in spec fuel could cause serious flow issues, interfacing with a mechanical system that potentiates it. Follow on melting and refreeze would be indicative of such a concentration, though "in Spec."
I don't recall if anyone has brought up "downstream" cavitation.
Fuel in general: Storage, transport, transfer, etc.
BA038: sumping negligence, lack of critical procedure compliance
(Would apply to other carriers of course.)
There seems to be an unwillingness to address wet fuel other than spec measurement and an eagerness to eliminate contaminated supplies. Instead, the drill is "Undiscovered fuel characteristics, etc." at very low temp...
The Trent has an exposure here, vis a vis FOHE and other plumbing.
A very small amount of ice, perhaps present in barely nucleated crystals, could deposit over time in restricted flow areas. In other words, in spec fuel could cause serious flow issues, interfacing with a mechanical system that potentiates it. Follow on melting and refreeze would be indicative of such a concentration, though "in Spec."
I don't recall if anyone has brought up "downstream" cavitation.
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nu·cle·at·ed (nkl-td, ny-)
adj.
Having a nucleus or nuclei: the nucleated cell of a spermatozoon.
Hope that helps! Sadly, that's about as much as I can contribute to this runaway train of a thread.
adj.
Having a nucleus or nuclei: the nucleated cell of a spermatozoon.
Hope that helps! Sadly, that's about as much as I can contribute to this runaway train of a thread.
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nucleated droplet mechanism -- Britannica Online Encyclopedia
nucleated - definition of nucleated in the Medical dictionary - by the Free Online Medical Dictionary, Thesaurus and Encyclopedia.
nucleated - Definition from the Merriam-Webster Online Dictionary
nucleated - definition of nucleated by the Free Online Dictionary, Thesaurus and Encyclopedia.
I really should stop digressing!!!!
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As a non-professional, I hesitate to stick my nose in here,
The FOHE seems to be the fundamental difference in the two alternative power-plants.
The Trent would appear to have chilling problems, due to low flow of hot oil, when power demand is low.
Is it beyond reason to use an "electric blanket" type heater, thermostatically controlled, for those low-power, low fuel-flow situations when this fuel-icing becomes prevalant?
I appreciate there would be a substantial electric load involved, but the engine would have plenty of POTENTIAL power-reserve to cope, it being my understanding that the problem ONLY occurs when there is very low power demand in a very low ambient temperature..
another source of heat may be bleed-air?
or should I keep my nose out?
The FOHE seems to be the fundamental difference in the two alternative power-plants.
The Trent would appear to have chilling problems, due to low flow of hot oil, when power demand is low.
Is it beyond reason to use an "electric blanket" type heater, thermostatically controlled, for those low-power, low fuel-flow situations when this fuel-icing becomes prevalant?
I appreciate there would be a substantial electric load involved, but the engine would have plenty of POTENTIAL power-reserve to cope, it being my understanding that the problem ONLY occurs when there is very low power demand in a very low ambient temperature..
another source of heat may be bleed-air?
or should I keep my nose out?
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Fluency in Fluids
What's one plausible relationship between:
1. the incident below at bottom (which, according to latest ATSB revelations a few days ago, remains insoluble),
2. BA038 and
3. the A320 crash off Perpignan [Toulouse] (and maybe a few others)?
.
Answer:
The ability of water to free-flow migrate to different parts of a labyrinthine piped system, be it LP fuel or static air line - and coalesce into a static and blocking frozen mass, obstructing flow-rates and constricting sensor input data pick-offs. Think suddenly replacing engine oil with heavy duty grease.
Explanation:
A. When water is in solution in fuel or merely a frozen lump attached to a crevice in a tank, it's harmless. When water is free-flowing in a pneumatic static air pressure system all it does is slightly/imperceptibly dampen rates (ASI speed-changes, VSI, altimeters).
However when an icy lump dislodges due to fuel level changes, turbulence, warming, structural flexure etc, it can rapidly move, without any symptoms, to a position where it can critically obstruct flows.
.
B. When water in a static line moves to an area where it can freeze and obstruct ambient pressure changes from reaching sensitive transducers, then ADIRU data can become corrupted. This can happen suddenly and, courtesy of the software, produce abrupt and unexpected results. Think the difference between anti-skid braking on a slippery surface at 100knots - and simply selecting the parkbrake ON (at that speed).
The point being made is that the metamorphosis from free-flowing water to static and obstructionist ice-block is very capable of defeating system design software and producing sudden unexpected outcomes.
Not a lot is known about the behavior of water in a system of non-homogenous temperatures that is also subject to a wide range of flow-rates
.
When that metamorphosis is transitory and ephemeral, the phenomenon can be a difficult one to envisage, let alone replicate. It's the same problem with a wiring fire. Did the wiring flash-over and a fire cause the crash OR was all that burnt wiring just burnt in the post-crash fire?
.
Those of us ho have experienced the rapid confusing loss of flight instrumentation in the climb due to frozen pitot or stati lines will be ready converts to this theory. Those who went on to fly modern aircraft where the same systems can become flummoxed by such data corruptions would be less easily convinced - unless they were participants in the incidents mentioned (or similar). If you're not convinced about the effect that water can have upon a computer, I urge you to empty an ice-tray on your keyboard and stand back.
**************************************************
At 0932 local time (0132 UTC) on 7 October 2008, an Airbus A330-303 aircraft, registered VH-QPA, departed Singapore on a scheduled passenger transport service to Perth, Australia. On board the aircraft (operating as flight number QF72) were 303 passengers, nine cabin crew and three flight crew. At 1240:28, while the aircraft was cruising at 37,000 ft, the autopilot disconnected. That was accompanied by various aircraft system failure indications. At 1242:27, while the crew was evaluating the situation, the aircraft abruptly pitched nose-down. The aircraft reached a maximum pitch angle of about 8.4 degrees nose-down, and descended 650 ft during the event. After returning the aircraft to 37,000 ft, the crew commenced actions to deal with multiple failure messages. At 1245:08, the aircraft commenced a second uncommanded pitch-down event. The aircraft reached a maximum pitch angle of about 3.5 degrees nose-down, and descended about 400 ft during this second event.
At 1249, the crew made a PAN emergency broadcast to air traffic control, and requested a clearance to divert to and track direct to Learmonth. At 1254, after receiving advice from the cabin crew of several serious injuries, the crew declared a MAYDAY. The aircraft subsequently landed at Learmonth at 1350.
Currently available information indicates that one flight attendant and at least 13 passengers were seriously injured and many others experienced less serious injuries. Most of the injuries involved passengers who were seated without their seatbelts fastened. This constituted an accident under the ICAO definition outlined in Annex 13 to the Chicago Convention and as defined in the Transport Safety Investigation Act 2003.
Examination of flight data recorder information indicates that, at the time the autopilot disconnected, there was a fault with the inertial reference (IR) part of the air data inertial reference unit (ADIRU) number 1. From that time, there were many spikes in the recorded parameters from the air data reference (ADR) and IR parts of ADIRU 1. Two of the angle-of-attack spikes appear to have been associated with the uncommanded pitch-down movements of the aircraft.
Download complete report [PDF 1.2 MB]
1. the incident below at bottom (which, according to latest ATSB revelations a few days ago, remains insoluble),
2. BA038 and
3. the A320 crash off Perpignan [Toulouse] (and maybe a few others)?
.
Answer:
The ability of water to free-flow migrate to different parts of a labyrinthine piped system, be it LP fuel or static air line - and coalesce into a static and blocking frozen mass, obstructing flow-rates and constricting sensor input data pick-offs. Think suddenly replacing engine oil with heavy duty grease.
Explanation:
A. When water is in solution in fuel or merely a frozen lump attached to a crevice in a tank, it's harmless. When water is free-flowing in a pneumatic static air pressure system all it does is slightly/imperceptibly dampen rates (ASI speed-changes, VSI, altimeters).
However when an icy lump dislodges due to fuel level changes, turbulence, warming, structural flexure etc, it can rapidly move, without any symptoms, to a position where it can critically obstruct flows.
.
B. When water in a static line moves to an area where it can freeze and obstruct ambient pressure changes from reaching sensitive transducers, then ADIRU data can become corrupted. This can happen suddenly and, courtesy of the software, produce abrupt and unexpected results. Think the difference between anti-skid braking on a slippery surface at 100knots - and simply selecting the parkbrake ON (at that speed).
The point being made is that the metamorphosis from free-flowing water to static and obstructionist ice-block is very capable of defeating system design software and producing sudden unexpected outcomes.
Not a lot is known about the behavior of water in a system of non-homogenous temperatures that is also subject to a wide range of flow-rates
.
When that metamorphosis is transitory and ephemeral, the phenomenon can be a difficult one to envisage, let alone replicate. It's the same problem with a wiring fire. Did the wiring flash-over and a fire cause the crash OR was all that burnt wiring just burnt in the post-crash fire?
.
Those of us ho have experienced the rapid confusing loss of flight instrumentation in the climb due to frozen pitot or stati lines will be ready converts to this theory. Those who went on to fly modern aircraft where the same systems can become flummoxed by such data corruptions would be less easily convinced - unless they were participants in the incidents mentioned (or similar). If you're not convinced about the effect that water can have upon a computer, I urge you to empty an ice-tray on your keyboard and stand back.
**************************************************
At 0932 local time (0132 UTC) on 7 October 2008, an Airbus A330-303 aircraft, registered VH-QPA, departed Singapore on a scheduled passenger transport service to Perth, Australia. On board the aircraft (operating as flight number QF72) were 303 passengers, nine cabin crew and three flight crew. At 1240:28, while the aircraft was cruising at 37,000 ft, the autopilot disconnected. That was accompanied by various aircraft system failure indications. At 1242:27, while the crew was evaluating the situation, the aircraft abruptly pitched nose-down. The aircraft reached a maximum pitch angle of about 8.4 degrees nose-down, and descended 650 ft during the event. After returning the aircraft to 37,000 ft, the crew commenced actions to deal with multiple failure messages. At 1245:08, the aircraft commenced a second uncommanded pitch-down event. The aircraft reached a maximum pitch angle of about 3.5 degrees nose-down, and descended about 400 ft during this second event.
At 1249, the crew made a PAN emergency broadcast to air traffic control, and requested a clearance to divert to and track direct to Learmonth. At 1254, after receiving advice from the cabin crew of several serious injuries, the crew declared a MAYDAY. The aircraft subsequently landed at Learmonth at 1350.
Currently available information indicates that one flight attendant and at least 13 passengers were seriously injured and many others experienced less serious injuries. Most of the injuries involved passengers who were seated without their seatbelts fastened. This constituted an accident under the ICAO definition outlined in Annex 13 to the Chicago Convention and as defined in the Transport Safety Investigation Act 2003.
Examination of flight data recorder information indicates that, at the time the autopilot disconnected, there was a fault with the inertial reference (IR) part of the air data inertial reference unit (ADIRU) number 1. From that time, there were many spikes in the recorded parameters from the air data reference (ADR) and IR parts of ADIRU 1. Two of the angle-of-attack spikes appear to have been associated with the uncommanded pitch-down movements of the aircraft.
Download complete report [PDF 1.2 MB]
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This Flight Global article is interesting. It explains the AD, and how the GE and PW FOHE installations are different from the Trent 895.
Boeing links Heathrow, Atlanta Trent 895 engine rollbacks
Boeing links Heathrow, Atlanta Trent 895 engine rollbacks
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Clear
What's becoming clear from this last release by Boeing is a possible genesis for the "behaviour hitherto unseen of Fuel".
Though in spec., fuel does have some content of water. It "freezes", but more along the lines of fine granules, that behave more like a "particulate" than a common picture of "Ice". As the "slurry" (my term) migrates through the fuel plumbing it can be deposited in a number of ways on surfaces and openings. Given time, this deposition can impede the flow. The added "pressure" of enhanced HP input may serve only to exacerbate the problem, perhaps dislodging deposits to be more occlusive downstream. Melting this "powdery plug" evidently solves the problem, interpreting the AD and its reference to PW and GE.So the fix is in modifying the geometry of the FOHE, its placement, capacity or orifices.
So Far.
Though in spec., fuel does have some content of water. It "freezes", but more along the lines of fine granules, that behave more like a "particulate" than a common picture of "Ice". As the "slurry" (my term) migrates through the fuel plumbing it can be deposited in a number of ways on surfaces and openings. Given time, this deposition can impede the flow. The added "pressure" of enhanced HP input may serve only to exacerbate the problem, perhaps dislodging deposits to be more occlusive downstream. Melting this "powdery plug" evidently solves the problem, interpreting the AD and its reference to PW and GE.So the fix is in modifying the geometry of the FOHE, its placement, capacity or orifices.
So Far.
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From the Flight Global article, it appears the GE and PW design recirculates some of the heated fuel back to the upstream face of the FOHE, thus preheating the new cold fuel approaching the upstream FOHE face (thus melting any water ice before reaching the FOHE). The Trent FOHE does not appear to have this warmed fuel recirculation feature, thus the fuel reaching the upstream face of the FOHE is colder than on the GE or PW designs.
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Agreed
But I think there may be more to it. I don't think just cold temps are the culprit. I know I am inferring something here, but don't forget the additional plumbing in GE/PW in itself may be a bottleneck under certain circumstances. What's missing here is the "unseen characteristics" of fuel.
Now that may be some red Herring to "exonerate" the Trent, but I have to doubt it.
What hasn't been addressed as far as I know is the possibility that Fuel at very low temps, infused with some concentration of hard small "particle ice", may be behaving like a colloidal suspension rather than a homogeneous fluid. If that is so, centrifugal force, gravity and pressure would make Fuel behave like a "slurry". At certain shape and minimum size, a deposit of powdery water ice could cause all sorts of problems as it changes location, hardness, and size at will. Think "Plaque".
Just as most engines have a "bypass" for oil past its filtration, to continue flow, doesn't the Trent have an FOHE bypass? For Fuel? To avoid a plug and keep the injectors happy?
AF
Now that may be some red Herring to "exonerate" the Trent, but I have to doubt it.
What hasn't been addressed as far as I know is the possibility that Fuel at very low temps, infused with some concentration of hard small "particle ice", may be behaving like a colloidal suspension rather than a homogeneous fluid. If that is so, centrifugal force, gravity and pressure would make Fuel behave like a "slurry". At certain shape and minimum size, a deposit of powdery water ice could cause all sorts of problems as it changes location, hardness, and size at will. Think "Plaque".
Just as most engines have a "bypass" for oil past its filtration, to continue flow, doesn't the Trent have an FOHE bypass? For Fuel? To avoid a plug and keep the injectors happy?
AF
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I just question in the different return fuel routeing ahead of the FOHE on the GE and PW.
Had they experienced the iceing problem beforehand?
Was it just a convienent place to connect the return?
While sounding simple to reroute the return fuel ahead of the FOHE on the RR it will obviously take time to manufacture, fit and test parts involved to see if that will solve the problem.
VFD
Had they experienced the iceing problem beforehand?
Was it just a convienent place to connect the return?
While sounding simple to reroute the return fuel ahead of the FOHE on the RR it will obviously take time to manufacture, fit and test parts involved to see if that will solve the problem.
VFD