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AF,
Several of the posters on this thread probably a) fly for BA, b) are in or know Management c), have contacts in the AAIB/NTSB/RR (or are employed by one of these organisations), d) have a personal interest in the outcome of any investigations or a combination of all of these. They are probably also keenly aware of the media interest in this event and do not want to publicise things that may be confidential at this time unless explained in the most general terms. I don't think a request for detailed references will provide much at the moment... Sorry. |
airfoilmod,
See my post #1689 of 2 September. rgds |
Flipping back to that page I also notice my response to Viking soon after...
Originally Posted by Viking
Feels it has been too long now... Someone trying to hide anything maybe? Or just hoping that people "forget" about the whole thing? Yay- more speculations
Imagine if I looked further I'd see a wrap on the knuckles for that, :ouch: |
When people say that boeing are "testing the Trent" I PRESUME what they mean is that they are testing the pipework arrangements associated with the Trent type of installation as the engine per se isn't (???????) at fault but its fuel feed, system. I remember from very much earlier in the thread that the Trent and GE pipework set up varies in various details.
When the AAIB and Boeing comes up with some solution to the Trent set-up then whilst that might be worth it JUST for the Trent 777s, it won't really be a full solution until the results can be extended into all aircraft and engine types. AS AN UNINFORMED person I still find two things troubling ; - 1: People still seem to be talking about "ice" whereas the initial reports, etc.... all SEEM to say there is insufficient water to cause the problem, so something else ("waxing" or a. n. other) might be involved. Can anyone clarify ? - 2: IF whatever is eventually found to be the cause is a icing and/or "waxing" or whatever problem, I still find the almost simultaneous and exactly the same occurances in two separate systems amazing. and lastly, I will be fascinating to see what the eventual fuel spec will say (or whether they will set different flight profiles for different aircraft). . |
Limited info
The recent AD seems to admit that similar (very similar) fuel feed troubles might happen, and so they recommend some preventive actions.
Authorities keep silent about one information and one procedure that might have saved the day, and according to the hypothesis of trouble reccurence, would as well save other flights in the future. The information : best glide speed (or AOA) in different configuration (landing config, approach config ...) The procedure : permissible cleanup actions as required in such dramatical circumstances. In the las 12 months, we learned that multiple engine failures are not as exceptionnal as we think ... Perhaps less exceptionnal than a single engine failure right at V1, on a limited runway ... |
Best glide speed is published in dual engine flameout checklist for other Boeing products.
Flying 101, slow flight, is that the slower you go, beyond a certain point, the more power you need to overcome the drag. Configured that point is about Vref. |
Accidents often advance knowledge. TWA 800 resulted in additional testing that uncovered more knowledge about fuel tank heating, and unknown localized hot spots, in fuel tanks.
We shouldn't be surprised if BA038 uncovers new knowledge about fuel either. The real world can be different than the best lab. |
Flying 101, slow flight, is that the slower you go, beyond a certain point, the more power you need to overcome the drag. Configured that point is about Vref. I think most advice about gliding powered aircraft is written assuming a clean configuration... The wheels/flaps only come out when a landing is assured and you need to lose some energy. A 777 gear down, F30, Vref and no power I'd reckon you'd be lucky to get 7:1 out of it, rather than the 19:1 you need for a 3deg glide. |
Fullwings - question was posed to engineer that has access to the L/D data for different configurations - "Vapp (Vref+5) is close enough to not worry about the difference."
I don't have the exact data, just the word of an expert. This could be researched in a sim. Level flight(to increase fuel flow/N1's, and flight test various speeds and configurations. Lowest power required wins. 1.2 Vso? Have to double check my manuals but I think we always have 1.3Vso protection on arrival, 1.2Vso protection on departure. Best glide is for clean(ie, best glide configuration). Agree that configurated would be much worse. If my math is correct BA038 did 6:1 at Vref -27 kts. I'll see if I can figure out glide ratio closer to Vapp in my next sim session. |
You will excuse me if I take exception to your posts and to Mr. Mouse's ill founded support. I know what I know, you choose to accept or dismiss it as you see fit. Because you do not like not knowing is not really my problem or even of any interest. |
Phil gollin,
See my post 1689 of 2 September. What follows is speculation, but consider this. Boeing, RR and the AAIB realized that there was not enough water to produce a sufficient quantity of ice to restrict that fuel to the engines and concluded that other factors were in play. They may suspect or have discovered after carrying out CFD modelling, that the fuel they are analyzing has exhibited non-Newtonian properties at certain temperatures. Examples of non-Newtonian fluids (also known as complex fluids) are blood, paint, egg white, and many other sticky fluids. The nature of these complex fluids is known, but their properties and the changes they undergo are difficult to predict when it comes to transporting them in pipes. Not too much is known about the effect of temperature, the onset of turbulent flow, and the propensity for agglutination of these complex fluids. Regular jet fuel is a Newtonian fluid, as is water and other simple small molecule fluids. Perhaps the “exceeded spec.” fuel with a superior freezing point, displays non-Newtonian properties at certain temperatures depending on the architecture of the fuel delivery system? But this is idle speculation and largely a waste of time (as I think you said before) until we have more facts. |
Question from a confused lurker:
misd-agin writes:
This could be researched in a sim. Presumably the flight tests that validated the simulator model already have all this information. |
A Professional forum like this is really no place for puerile conspiracy theories... please desist.
Imagine if I looked further I'd see a wrap on the knuckles for that, Harry Mann, don't get too precious about it; this may be a professional forum, but the title of the site is Professional Pilots Rumour Network!! And whilst a small point, it is a 'rap' over the knucles unless you have a roll of brown paper, or any colour paper for that matter. |
What is happening with the aircraft. I have seen it a few times now at LHR behind some fencing and without the vertical tail vin.
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Ice around the edges?
We are told that the proportion of water in the fuel was too low for significant quantities of ice crystals to form in the bulk fuel in the tanks or in the bore of the pipework. But could some water have frozen out on the insides of the pipes themselves, in much the same way that water from fairly dry air builds up ice deposits over time on the cold plates of domestic fridges and freezers?
Any ice deposited in that way would probably be fairly soft and easily detached to clog up the FOHE by increased fuel flow as thrust was increased. |
And of course there is the assumption....
....that the fuel recovered was entirely representative of the bulk fuel loaded. If fuel stratification occurred, it is possible that the fuel that was being consumed in the hours before TOD was much higher in water content than the average water content in the fuel as a whole when loaded.
The theory has already been advanced in PPrune that in a steady-state (cruise) condition the ice accreting on the face of the FOHE was removed at a rate equal to its deposition and that it was only when the flow dropped during descent that the equilibrium changed (despite higher OAT) and ice buildup began. When the aircraft piled in, the remaining fuel that didnt leak de-stratified and the ice remixed as dissolved water, and the ice that built up in transit from wing to engine dropped out mainly as free water (because the concentration of water to fuel was higher in the lines) ("ingress of fire fighting foam" doesnt do it for me). Because the proportion of water consumed during the flight was higher than that in the bulk of the fuel loaded, it follows that the concentration of water in the remaining bulk fuel at the end of the flight - into which the ice redissolved - would be less. IF, repeat IF you accept that buildup model, then you also have to accept that it is possible that the water content of the fuel sampled at end of journey may not have been the same as that loaded prior to departure and that the water content in the fuel delivered to the FOHE was not homogenous during the flight. Anyone who has experience of returning to a frozen Margarita on a hot day after an extended potty break knows what I am suggesting. Pinkman |
Of interest.
Refuel two aircraft at the same time with the same fuel. Action fuel/water drainage checks at 2/3 hours on one and do the other at 9/10 hours, results will tend to be different, more water will normally be recovered at the 9/10 hours checks. After a long smooth cruise could guess results would be the same. But now think the 777RR have new drills for crew to incease fuel flow to deal with the poss of water build up. |
Quote :
....... But now think the 777RR have new drills for crew to incease fuel flow to deal with the poss of water build up. unquote IF there is either a water in fuel or fuel behaviour problem then ALL aircraft types will need to be re-examined. It MAY be that some aircraft have set-ups which mean addiditional measures are needed - but ALL will need to be looked at. . |
IF there is either a water in fuel or fuel behaviour problem then ALL aircraft types will need to be re-examined. It MAY be that some aircraft have set-ups which mean addiditional measures are needed - but ALL will need to be looked at. |
I copied this out of CAPTDOUG's thread DAL rollback update Trent895
DAL rollback update/Trent895 -------------------------------------------------------------------------------- SUBJECT: 777-200/Trent 895 N862DA Thrust Rollback During Cruise - 26 November 2008 ------------------------------------------------------------------------------- UPDATE 1 UPDATE 1 UPDATE 1 UPDATE 1 ------------------------------------------------------------------------------- Reference a) provides Boeing's previous fleet communication of a 777-200 with Trent 895 engines that experienced an uncommanded thrust rollback on one engine while in level flight cruise at FL 390. The thrust rolled back to a level above idle on that engine, approximately 40 minutes after a VNAV step climb. The flight crew performed the Engine Response non-normal checklist, which restored full capability to the engine for the remainder of the flight. The other engine operated normally throughout the flight. Based on the FDR data and the characteristics of the roll-back, it is suspected that accumulation of water ice in the fuel path of the Fuel Oil Heat Exchanger is the cause of the subject incident. Although the circumstances are slightly different, the subject incident is believed to have been caused by similar factors as those experienced in the 777-200ER G-YMMM accident at London, Heathrow airport on 17 January 2008 as described by Reference b). Investigation Status It should be emphasized that the investigations into both events are not yet complete, with the G-YMMM accident under an open investigation by the UK AAIB and the subject roll-back incident under an open investigation by the US NTSB. Boeing, Rolls-Royce, the operators and other organizations are supporting both investigations. Recommended Operator Action The circumstances of the subject thrust roll-back incident have led Boeing to review the cold fuel operations procedures released by Reference c). Based on this review, it is believed to be prudent to revise the interim mitigating procedures to account for what was learned in the subject roll-back incident. Changes to the interim procedures include: Reduce the window at top of descent from 3 to 2 hours; Assure the crossfeed valves are closed; Assure minimum idle thrust for 30 seconds during initial descent, and; Clarify the Condition statement in Engine Response Non-Normal Checklist (NNC). Reference d) provides a list of publications from Boeing that give the full definition of the revised interim mitigating procedures. The FAA and EASA are expected to release regulatory action to mandate use of the revised procedures. These procedures are interim measures that will remain in place until a permanent solution can be defined, tested, certified, and deployed to the fleet. Other Airframe/Engine Combinations These interim mitigation procedures only apply to 777s powered by Rolls-Royce Trent 800 engines and do not apply to other airframe/engine combinations. Based on our knowledge of the system configurations, scenario studies, and laboratory test results, we do not believe that immediate action is necessary or warranted for 777s powered by other engine types or non-777 airframes regardless of engine type. Studies of the applicability of the thrust roll back circumstances to other engine types and airframes are in work and will continue. Boeing will notify operators of the results of those studies as appropriate. Tom Dodt Chief Engineer - Air Safety Investigation The Boeing Company Download this as a file |
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? |
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 ? |
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! |
Flight Idle
Five liters? I have no idea. lomapaseo ?
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Airfoilmod:
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. |
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. |
nucleated |
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. ;) |
Originally Posted by M.Mouse
(Post 4691899)
What does that word mean, I cannot find it in either the UK or American dictionaries?
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!!!! |
It means granulated
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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? |
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] |
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 |
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. |
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 |
AF, if it did have the bypass, I suspect we wouldn't be discussing this accident.
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F S
Rhetorical, my friend, bad sarcasm even.
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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 |
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