BA038 (B777) Thread
Large Plumbing
The B777 uses two of just about the most powerful engines in the business, so each engine is presumably fed by some of the largest fuel lines in service.
Strange that this very fuel plumbing may have provided the first recorded example of an engine suffering serious fuel starvation due to a major blockage caused by gradual ice accretion, despite the contents of the fuel tanks being of good quality.
It is suggested that this may have been brought about because the engines were not operated at climb power again after the initial top-of-climb, but at slightly lower (cruise) power settings.
During the last several decades, how many other long-haul jet-transport engine-fuel systems − from those feeding Speys on G2s, through aircraft with engines of ascending fuel flows like (for example) JT3Ds on B707s, DC-8s and C-141s; to CF6s, JT9Ds and RB211s on various aircraft − have been operated successfully at similar altitudes and temperatures to BA038, for similar flight times, often without the application of climb power after initial TOC?
There’s nothing new or particularly unusual in crews avoiding the unnecessary use of climb power when an aeroplane is light.
What’s so special about the B777-Trent? Does anyone find the hypothesis convincing?
Strange that this very fuel plumbing may have provided the first recorded example of an engine suffering serious fuel starvation due to a major blockage caused by gradual ice accretion, despite the contents of the fuel tanks being of good quality.
It is suggested that this may have been brought about because the engines were not operated at climb power again after the initial top-of-climb, but at slightly lower (cruise) power settings.
During the last several decades, how many other long-haul jet-transport engine-fuel systems − from those feeding Speys on G2s, through aircraft with engines of ascending fuel flows like (for example) JT3Ds on B707s, DC-8s and C-141s; to CF6s, JT9Ds and RB211s on various aircraft − have been operated successfully at similar altitudes and temperatures to BA038, for similar flight times, often without the application of climb power after initial TOC?
There’s nothing new or particularly unusual in crews avoiding the unnecessary use of climb power when an aeroplane is light.
What’s so special about the B777-Trent? Does anyone find the hypothesis convincing?
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infrequentflyer789 (#1978)
- Agree about noise and switch-off of OJ pumps.
- I have been through posts but not seen centre tank scavenge inlets, OJ pump inlets or drain valves relative to each other or side on view as to how far off floor. Of few pictures have seen, they include:
Sumping - http://panchromat.org/.misc/B777-doc...stallation.jpg
Vent picture - http://panchromat.org/.misc/B777-doc...ent_system.jpg
Pump - http://panchromat.org/.misc/B777-doc...stallation.jpg
Centre tank - http://www.pprune.org/3929959-post284.html
Engine fuel supply – ImageShack - Hosting :: 777engineug1.jpg
RR Trent parameters - http://rgl.faa.gov/Regulatory_and_Gu...E/E00050EN.pdf
Plan of fuel supply: ImageShack - Hosting :: 777fuelpw3.jpg
- Agree re burn rate - slight difference in main tank flow rate just before and then after scavenge finishes.
- Agree re context of remark in AAIB report - my point was more that it seemed to suggest if gas then why not fluid could move through inactive OJ pump with suitable pressure differential? [I had an obscure "March Hare" theory a few posts back that air might be dissolved/entrained into main tank fuel as result of operation of centre tank fuel scavenge when CWT dry and as a result (i) subsequent release of undissolved air from air-saturated fuel into suction feed pipe and/or fuel manifold near OJ/ jettison check valve [or, before cavitation (as cause) ruled out, in HP pump] and (ii) so suction feed restricted by undissolved air and/or undissolved air near OJ/ jettison check valve end might allow localised low pressure fluctuations induced by cycling to result in OJ/ jettison check valve opening if surge of pressure in centre tank on fast descent, thereby introducing water slug (not air) to fuel manifold. In my dream world both the Mad Hatter and March Hare were coming to tea.]
- Agree that will have compared fuel data and that of previous flight.
Anyway it seems there is still quite a bit of Boeing testing to be done on the cascade of contributory factors leading to the location of the 95% restriction in the underlying fuel system, and the tentative, conflicting scenarios to date.
Perhaps the expense of putting a bit more flight test kit where not normally found in tanks and supply lines of a real plane (with correct geometry) and then flying it would be worth it (maybe could add water to centre tank and lower the temp of fuel in one of the main tank before uplifting it to cut to the chase, etc) ... since a double rollback is not just unusual but after all a surprisingly serious failure condition in an otherwise excellent aircraft.
- Agree about noise and switch-off of OJ pumps.
- I have been through posts but not seen centre tank scavenge inlets, OJ pump inlets or drain valves relative to each other or side on view as to how far off floor. Of few pictures have seen, they include:
Sumping - http://panchromat.org/.misc/B777-doc...stallation.jpg
Vent picture - http://panchromat.org/.misc/B777-doc...ent_system.jpg
Pump - http://panchromat.org/.misc/B777-doc...stallation.jpg
Centre tank - http://www.pprune.org/3929959-post284.html
Engine fuel supply – ImageShack - Hosting :: 777engineug1.jpg
RR Trent parameters - http://rgl.faa.gov/Regulatory_and_Gu...E/E00050EN.pdf
Plan of fuel supply: ImageShack - Hosting :: 777fuelpw3.jpg
- Agree re burn rate - slight difference in main tank flow rate just before and then after scavenge finishes.
- Agree re context of remark in AAIB report - my point was more that it seemed to suggest if gas then why not fluid could move through inactive OJ pump with suitable pressure differential? [I had an obscure "March Hare" theory a few posts back that air might be dissolved/entrained into main tank fuel as result of operation of centre tank fuel scavenge when CWT dry and as a result (i) subsequent release of undissolved air from air-saturated fuel into suction feed pipe and/or fuel manifold near OJ/ jettison check valve [or, before cavitation (as cause) ruled out, in HP pump] and (ii) so suction feed restricted by undissolved air and/or undissolved air near OJ/ jettison check valve end might allow localised low pressure fluctuations induced by cycling to result in OJ/ jettison check valve opening if surge of pressure in centre tank on fast descent, thereby introducing water slug (not air) to fuel manifold. In my dream world both the Mad Hatter and March Hare were coming to tea.]
- Agree that will have compared fuel data and that of previous flight.
Anyway it seems there is still quite a bit of Boeing testing to be done on the cascade of contributory factors leading to the location of the 95% restriction in the underlying fuel system, and the tentative, conflicting scenarios to date.
Perhaps the expense of putting a bit more flight test kit where not normally found in tanks and supply lines of a real plane (with correct geometry) and then flying it would be worth it (maybe could add water to centre tank and lower the temp of fuel in one of the main tank before uplifting it to cut to the chase, etc) ... since a double rollback is not just unusual but after all a surprisingly serious failure condition in an otherwise excellent aircraft.
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As posted by infrequentflyer789:
The 777 is ARINC 629 bus, which is multi-transmitter (and more advanced than anything other big jet until you get to 664 / AFDX on the A380 / 787), which should provide a lot of help with this issue.
The 777 is ARINC 629 bus, which is multi-transmitter (and more advanced than anything other big jet until you get to 664 / AFDX on the A380 / 787), which should provide a lot of help with this issue.
As posted by Backoffice:
I see this ice, whether it be from water in the fuel or the result of condensation being a sudden release, either due to temperature, flexing of the wing or vibration, of ice which has frozen and adhered to internal wing surfaces during the flight.
I see this ice, whether it be from water in the fuel or the result of condensation being a sudden release, either due to temperature, flexing of the wing or vibration, of ice which has frozen and adhered to internal wing surfaces during the flight.
It seems to me that whatever amount of water was present in the tanks during this period with ground times of 48 hours and 20 hours respectively, most of it, if present, would have been drained. In addition, refueling at Heathrow (according to the AAIB) occurred only after sumping for water, any condensation adhering to the interior structure (water, not ice with so many hours of temps. well above freezing) would have been absorbed by the fuel during refueling and would not have had time to settle at the bottom of the tanks before the flights took place.
As posted by Chriss Scott:
What’s so special about the B777-Trent? Does anyone find the hypothesis convincing?
What’s so special about the B777-Trent? Does anyone find the hypothesis convincing?
No, i do not find the hypothesis convincing, especially when the weather conditions and actions taken to drain water while on the ground for considerable times at Heathrow are taken into account.
Green-dot
Last edited by Green-dot; 14th Sep 2008 at 10:38. Reason: Clarification.
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Chris Scott wrote:
"The B777 uses two of just about the most powerful engines in the business, so each engine is presumably fed by some of the largest fuel lines in service.
Strange that this very fuel plumbing may have provided the first recorded example of an engine suffering serious fuel starvation due to a major blockage caused by gradual ice accretion, despite the contents of the fuel tanks being of good quality."
Well, if you think about it, having a larger diameter pipe to allow higher flow at full power means that the effects of low power and fuel flow for long periods are exacerbated, the fuel is moving more slowly because a given volume travels more slowly through a larger diameter pipe. Hence, if this is down to ice accretion on the pipe walls, there is more time for an ice crystal passing accreted ice to stick to it.
"The B777 uses two of just about the most powerful engines in the business, so each engine is presumably fed by some of the largest fuel lines in service.
Strange that this very fuel plumbing may have provided the first recorded example of an engine suffering serious fuel starvation due to a major blockage caused by gradual ice accretion, despite the contents of the fuel tanks being of good quality."
Well, if you think about it, having a larger diameter pipe to allow higher flow at full power means that the effects of low power and fuel flow for long periods are exacerbated, the fuel is moving more slowly because a given volume travels more slowly through a larger diameter pipe. Hence, if this is down to ice accretion on the pipe walls, there is more time for an ice crystal passing accreted ice to stick to it.
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Pumps in series
dxzh, in re your post #1969 of yesterday, on page 99:
Centrifugal pumps of conventional design can be operated in series; I have done design work with such arrangements. It does not matter if the upstream pump (in this case) loses its electrical power. There are no in-built internal obstructions to continued flow through a centrifugal pump whether or not its impeller is still free to turn, or siezed in its bearings.
It is conceivable that the housing of such a pump could be fitted with a stop valve held open by a solenoid energized by current from the pump power circuit. I haven't seen any indication that the 777 pumps of which I have details (Eaton Aerospace (UK) wing tank LP boost) have any such feature. This seems undesirable in an aircraft, just my opinion. I've seen systems (non-aircraft) that had such a feature, but only as a separate valve in the piping.
As to air entering the engine LP pump suction, I can only address the fuel path from the main wing tanks. Here the wing tank suction points are above the engine fuel feed in such a way that the engine LP pump would normally operate with a gravity-flooded suction if fed entirely from the wing on that side, with the LP boost pumps of that side off. I can't say I see this as even remotely likely in the air, and use it only by way of example (lacking as yet sufficient info regarding elevations in the center tank plumbing).
Anyway, with a fuel velocity of at most 7 feet per second (8 possibly), I cannot see it likely that significant air would be entrained should the suction of one of the wing LP boost pumps become unflooded itself due to fuel slosh. It isn't like the engine pump was above the fuel source. BTW, the velocity given is for a fuel rate of 35,000 lbs/hr. This is the conventional maximum velocity (for avoiding static charge on the fuel), and may also be seen from the near 2" discharge diameter of the wing LP boost pump casting.
The same principles would apply to the center tanks, but as noted I don't know the elevations of the various components clearly enough to comment. The dimensional detail of the wing LP boost pumps in on the Eaton Aerospace website; earlier I forgot to mention that it is not in the brochures-- instead look under "downloads" for the data sheets, including B777-300 for a comparison to the -200.
Following what I consider to be good example, I stand to be corrected in this matter if necessary. Well, it is a somewhat complex fuel system, although I think it is robust, simple in components and backup/bypass paths, and extremely reliable, at least until now.
OE
Is it a red herring even to contemplate the boost pumps or centre tank pumps allowing the passage of fuel/water when they are selected OFF? I guess the premise of the suction feed test on the ground (as a pure test of the suction feed) would be flawed if it was a possibility that an engine-driven LP could draw fuel through any of the unpowered pumps from centre tank - and thus I would like to discount the idea completely. Yet as a Mad Hatter is drawn to a tea party, I am curious about the possibility given the suggestion in the interim report that air at least might possibly pass through the OJ/jettison check valve (and presumably therefore through the OJ pump when selected OFF too) ...
It is conceivable that the housing of such a pump could be fitted with a stop valve held open by a solenoid energized by current from the pump power circuit. I haven't seen any indication that the 777 pumps of which I have details (Eaton Aerospace (UK) wing tank LP boost) have any such feature. This seems undesirable in an aircraft, just my opinion. I've seen systems (non-aircraft) that had such a feature, but only as a separate valve in the piping.
As to air entering the engine LP pump suction, I can only address the fuel path from the main wing tanks. Here the wing tank suction points are above the engine fuel feed in such a way that the engine LP pump would normally operate with a gravity-flooded suction if fed entirely from the wing on that side, with the LP boost pumps of that side off. I can't say I see this as even remotely likely in the air, and use it only by way of example (lacking as yet sufficient info regarding elevations in the center tank plumbing).
Anyway, with a fuel velocity of at most 7 feet per second (8 possibly), I cannot see it likely that significant air would be entrained should the suction of one of the wing LP boost pumps become unflooded itself due to fuel slosh. It isn't like the engine pump was above the fuel source. BTW, the velocity given is for a fuel rate of 35,000 lbs/hr. This is the conventional maximum velocity (for avoiding static charge on the fuel), and may also be seen from the near 2" discharge diameter of the wing LP boost pump casting.
The same principles would apply to the center tanks, but as noted I don't know the elevations of the various components clearly enough to comment. The dimensional detail of the wing LP boost pumps in on the Eaton Aerospace website; earlier I forgot to mention that it is not in the brochures-- instead look under "downloads" for the data sheets, including B777-300 for a comparison to the -200.
Following what I consider to be good example, I stand to be corrected in this matter if necessary. Well, it is a somewhat complex fuel system, although I think it is robust, simple in components and backup/bypass paths, and extremely reliable, at least until now.
OE
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Quote: All of the testing and research of this accident has been conducted
on Boeing Model 777-200 and -300 series airplanes, equipped with Rolls-
Royce Model RB211-TRENT 800 series engines. Initial review of 777 other
airplane engine combinations has not revealed the same vulnerability to
the identified unsafe condition. End Quote.
Sounds like they are reasonably sure where the blockage occured and its somewhere specific to airframes plumbed for RR engines. Why wouldn't a similar release of ice be a hazard to other engines?
Edit: I was asked to post the source of the above quote. It came from this document posted earlier in this thread by "Precept"...
http://www.pprune.org/4391725-post1975.html
Justia Regulation Tracker Airworthiness Directives: Boeing Model 777-200 and -300 Series Airplanes Equipped with Rolls-Royce Model RB211-TRENT 800 Series Engines, - Federal Aviation Administration - 52909?52911 [E8?21138]
on Boeing Model 777-200 and -300 series airplanes, equipped with Rolls-
Royce Model RB211-TRENT 800 series engines. Initial review of 777 other
airplane engine combinations has not revealed the same vulnerability to
the identified unsafe condition. End Quote.
Sounds like they are reasonably sure where the blockage occured and its somewhere specific to airframes plumbed for RR engines. Why wouldn't a similar release of ice be a hazard to other engines?
Edit: I was asked to post the source of the above quote. It came from this document posted earlier in this thread by "Precept"...
http://www.pprune.org/4391725-post1975.html
Justia Regulation Tracker Airworthiness Directives: Boeing Model 777-200 and -300 Series Airplanes Equipped with Rolls-Royce Model RB211-TRENT 800 Series Engines, - Federal Aviation Administration - 52909?52911 [E8?21138]
Last edited by cwatters; 14th Sep 2008 at 19:19.
cwatters
please identify source of quote that you used in your post
Quote: All of the testing and research of this accident has been conducted
on Boeing Model 777-200 and -300 series airplanes, equipped with Rolls-
Royce Model RB211-TRENT 800 series engines. Initial review of 777 other
airplane engine combinations has not revealed the same vulnerability to
the identified unsafe condition. End Quote.
Sounds like they are reasonably sure where the blockage occured and its somewhere specific to airframes plumbed for RR engines. Why wouldn't a similar release of ice be a hazard to other engines?
on Boeing Model 777-200 and -300 series airplanes, equipped with Rolls-
Royce Model RB211-TRENT 800 series engines. Initial review of 777 other
airplane engine combinations has not revealed the same vulnerability to
the identified unsafe condition. End Quote.
Sounds like they are reasonably sure where the blockage occured and its somewhere specific to airframes plumbed for RR engines. Why wouldn't a similar release of ice be a hazard to other engines?
FAA Airworthiness Directive
Initial review of 777 other airplane engine combinations has not revealed the same vulnerability to the identified unsafe condition.
FR Doc E8-21138
Assuming this site to be legitimate (I think it is), it comes from the discussion portion of the Supplementary Information section for the AD being promulgated by the FAA in response to the incident which is the subject of this thread.
Last edited by archae86; 13th Sep 2008 at 22:39. Reason: add the subject quotation, and modify Title
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This FAA AD (for comment) amazes me - to put it mildly !
It would seem that whilst the lead autority (the AAIB) cannot assess what has happened and only speculates - the FAA SEEMS to have decided what happened, and more importantly that it couldn't happen to other engines on 777s ? (The AAIB thinks proper testing of other engine/airframe combinations are required).
Well - IF the FAA know it can't happen to other engines, maybe they can tell us (and the AAIB) what happened with the Trent supplies.
PLEASE can someone explain, as this doesn't make any sense to me.
.
It would seem that whilst the lead autority (the AAIB) cannot assess what has happened and only speculates - the FAA SEEMS to have decided what happened, and more importantly that it couldn't happen to other engines on 777s ? (The AAIB thinks proper testing of other engine/airframe combinations are required).
Well - IF the FAA know it can't happen to other engines, maybe they can tell us (and the AAIB) what happened with the Trent supplies.
PLEASE can someone explain, as this doesn't make any sense to me.
.
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Part 'g' has been written (in beta form if you like 
) for the AMM and is awaiting final approval. It has been tried and tested mainly to see if any improvements can be made (for example reducing the number of trips between the flt. deck and refuel panel) or whether it's a one or two person operation!
As regards the comment 'it can only happen to a RR Trent powered a/c' may stem from the fact that all the fuel system components are on the outside of the fan case. Whereas certainly for the GE90, all the components are around the core engine in a very warm environment. Other than the pylon area the airframe fuel system is identical.
) for the AMM and is awaiting final approval. It has been tried and tested mainly to see if any improvements can be made (for example reducing the number of trips between the flt. deck and refuel panel) or whether it's a one or two person operation! As regards the comment 'it can only happen to a RR Trent powered a/c' may stem from the fact that all the fuel system components are on the outside of the fan case. Whereas certainly for the GE90, all the components are around the core engine in a very warm environment. Other than the pylon area the airframe fuel system is identical.
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just suppose
what if the sumping was not done? For example the engineer just rubber stamped the job. I've heard it goes on. Now the aircraft has the free water thats needed to create the ice that caused the blockage that brought the craft down prematurely.
Just a thought;-)
Just a thought;-)
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About ten pages back, there seemed to be an emerging consensus that the reason the RR engine was being singled out for changes in operating procedures was the presence/position/design of the FOHE. If blocking of the heat exchanger was the immediate cause of the loss of power, then the time between the demand for increased thrust and the start of uncommanded power reduction could give an indication of where in the system the ice came from. I could dig out the time from the AAIB report, but I have no information on the speed of fuel flows or the geometry of the pipework. Does anyone in possession of the relevant information care to do the sums?
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Re: http://www.pprune.org/4392955-post1983.html
If refueling was done after sumping at LHR what about the possibility of contaminated fuel being loaded at LRH? Unlikely, but if I understand correctly they had a water alert at LHR? Say that water was correctly scavanged and sent to the engines causing a layer to build up in the plumbing (not enough to cause a problem in itself). The contaminated fuel would have been used up and replaced with good fuel in china. It was cold there so ice in plumbing (if not the tanks) might have remained frozen? Then on way back ice build up reduces until the last bit brakes off in chunks and causes the serious restriction. Result no water detected in the tanks.
If refueling was done after sumping at LHR what about the possibility of contaminated fuel being loaded at LRH? Unlikely, but if I understand correctly they had a water alert at LHR? Say that water was correctly scavanged and sent to the engines causing a layer to build up in the plumbing (not enough to cause a problem in itself). The contaminated fuel would have been used up and replaced with good fuel in china. It was cold there so ice in plumbing (if not the tanks) might have remained frozen? Then on way back ice build up reduces until the last bit brakes off in chunks and causes the serious restriction. Result no water detected in the tanks.
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However unlikely (it had crossed my mind as well), it could be a possibility but the AAIB most likely will have investigated such a scenario. Fuel in storage tanks, fuel hydrants and/or bowsers are also monitored for contamination and records are kept. If there would have been a contaminated batch of fuel originating from LHR, I'd suspect more aircraft would have been affected.
I know, it is quite speculative to say the AAIB will have investigated because none of their reports have confirmed that they did but knowing their thorough investigative track record, my guess is that they did.
Regarding the water alert, none of the AAIB reports sofar have confirmed the claim of a water alert for any of the flights referred to in these reports. I am sure that if it was an issue it would have surfaced in the most recent interim report.
Green-dot
I know, it is quite speculative to say the AAIB will have investigated because none of their reports have confirmed that they did but knowing their thorough investigative track record, my guess is that they did.
Regarding the water alert, none of the AAIB reports sofar have confirmed the claim of a water alert for any of the flights referred to in these reports. I am sure that if it was an issue it would have surfaced in the most recent interim report.
Green-dot
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Any chance there is a correlation in progress between the investigation authorities with respect to the BA38 and QF72 events regarding possible uncommanded system behaviour?
Green-dot
Green-dot