BA038 (B777) Thread
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Sunfish
At the point when the right
engine began to lose thrust the data indicated that the
right engine EEC responded correctly to a reduction
in fuel flow to the right engine, followed by a similar
response from the left EEC when fuel flow to the left
engine diminished.
it's in the report.
engine began to lose thrust the data indicated that the
right engine EEC responded correctly to a reduction
in fuel flow to the right engine, followed by a similar
response from the left EEC when fuel flow to the left
engine diminished.
it's in the report.
Throttle-up. Perceived discrepancy in FOB
Quote from autoflight:
Is anyone claiming that the crew opened the thrust levers to max and kept them there?
[Unquote]
Quote from AAIB Bulletin S1-2008 (Feb18):
The engines failed to respond to further demands for increased thrust from both auto-throttles, and subsequent movement of the thrust levers fully forward by the flight crew.
[Unquote]
Does that go any way towards answering your question?
CONF iture, Thanks for reminding me about the "250 kts 12D before LAM". I also think they are unlikely to have entered the hold at much above 230 kts, decelerating to their ideal holding IAS. I'm guessing this might have been about 210 - 220 kts, as they were light.
So I think it is likely that a significant amount of thrust would have been used in the hold (but see my previous post, above) to average only 400 ft/min ROD. By the way, a typical time taken from exit of the LAM hold to touchdown is 10 - 15 mins, depending on traffic. Even taking the quickest case, they are still likely to have used thrust (above idle) again while flying at a steady 160 kts, normally required by ATC for the segment between (roughly) 7 miles and 4 miles from the runway.
But, in the absence of the FDR/QAR data, this is all speculation...
Quote from CONF iture (discussing/quoting AAIB Bulletin):
“the total fuel on board was indicated 10500kg” and even if “both of the eng spar valves were found to be open, allowing the fuel leak evident at the accident site” they avoided to mention how much fuel they drained from the main tanks.
[Unquote]
You seem to be suggesting that the AAIB's economy in words may have been designed to cover some doubt they had about the indicated fuel quantity (FOB) on landing. I think it is likely that the indicated FOB the AAIB stated would have represented the lower of the following 2 figures:
1) total FOB in real time as measured by the FQI sysyem;
2) departure FOB (as entered into the FMS by the crew at Beijing) minus fuel used (as measured by the engine flowmeters); known as the CALCULATED FOB.
Method (2) does not, of course, take into account any leaks; nor (probably) any APU fuel consumption. The latter is not normally used after engine start; the former self-evident post-flight.
The stated FOB on landing being 3600 kgs higher than the F/P destination fuel could be accounted for by a number of (presently unknown) factors in combination. A ZFW lower than planned (as you are thinking?) would have saved 300-400 kgs of fuel per tonne on a 10-hour flight. Again, as you imply, we do not know how much flight time was saved (if any, due to better wind-components and/or direct routings). Contingency fuel is - for the purpose of calculating F/P FOB at destination - assumed NOT to be burned, so is probably irrelevant.
Finally, you will have noticed that TOD was at FL400, which is probably higher than planned, saving fuel for the last part of the cruise with their light payload. Also, the F/P included a temporary descent from FL341 to FL318 early on, which would have been costly in fuel; they avoided this at the request of ATC. The latter is the only known source of fuel saving for us at this stage.
In summary, there is already much known scope for fuel saving, and the unknowns may have even more to offer. I see no reason to infer (as I assume you are) that the AAIB may harbour doubts about the validity of the indicated FOB they published.
Is anyone claiming that the crew opened the thrust levers to max and kept them there?
[Unquote]
Quote from AAIB Bulletin S1-2008 (Feb18):
The engines failed to respond to further demands for increased thrust from both auto-throttles, and subsequent movement of the thrust levers fully forward by the flight crew.
[Unquote]
Does that go any way towards answering your question?
CONF iture, Thanks for reminding me about the "250 kts 12D before LAM". I also think they are unlikely to have entered the hold at much above 230 kts, decelerating to their ideal holding IAS. I'm guessing this might have been about 210 - 220 kts, as they were light.
So I think it is likely that a significant amount of thrust would have been used in the hold (but see my previous post, above) to average only 400 ft/min ROD. By the way, a typical time taken from exit of the LAM hold to touchdown is 10 - 15 mins, depending on traffic. Even taking the quickest case, they are still likely to have used thrust (above idle) again while flying at a steady 160 kts, normally required by ATC for the segment between (roughly) 7 miles and 4 miles from the runway.
But, in the absence of the FDR/QAR data, this is all speculation...
Quote from CONF iture (discussing/quoting AAIB Bulletin):
“the total fuel on board was indicated 10500kg” and even if “both of the eng spar valves were found to be open, allowing the fuel leak evident at the accident site” they avoided to mention how much fuel they drained from the main tanks.
[Unquote]
You seem to be suggesting that the AAIB's economy in words may have been designed to cover some doubt they had about the indicated fuel quantity (FOB) on landing. I think it is likely that the indicated FOB the AAIB stated would have represented the lower of the following 2 figures:
1) total FOB in real time as measured by the FQI sysyem;
2) departure FOB (as entered into the FMS by the crew at Beijing) minus fuel used (as measured by the engine flowmeters); known as the CALCULATED FOB.
Method (2) does not, of course, take into account any leaks; nor (probably) any APU fuel consumption. The latter is not normally used after engine start; the former self-evident post-flight.
The stated FOB on landing being 3600 kgs higher than the F/P destination fuel could be accounted for by a number of (presently unknown) factors in combination. A ZFW lower than planned (as you are thinking?) would have saved 300-400 kgs of fuel per tonne on a 10-hour flight. Again, as you imply, we do not know how much flight time was saved (if any, due to better wind-components and/or direct routings). Contingency fuel is - for the purpose of calculating F/P FOB at destination - assumed NOT to be burned, so is probably irrelevant.
Finally, you will have noticed that TOD was at FL400, which is probably higher than planned, saving fuel for the last part of the cruise with their light payload. Also, the F/P included a temporary descent from FL341 to FL318 early on, which would have been costly in fuel; they avoided this at the request of ATC. The latter is the only known source of fuel saving for us at this stage.
In summary, there is already much known scope for fuel saving, and the unknowns may have even more to offer. I see no reason to infer (as I assume you are) that the AAIB may harbour doubts about the validity of the indicated FOB they published.
Last edited by Chris Scott; 28th Feb 2008 at 01:29. Reason: 1 syntax error
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At the risk of stating the obvious, we don’t know exactly what caused this do we. What we do know is that there was air, fuel and operationally effective fuel pumps and functioning EEC control, according to the AAIB. Nevertheless, fuel flow was restricted. The question is how. We seem to have exhausted most possibilities. What might be helpful is for someone to run a CFD programme using the same temperature and demand regime experienced by BA 038. Is anyone on here able to do this, or perhaps know someone who might?
Jetdoc,
Thank you for the further information. How do the refuel valves function physically and where are they in the main (wing) tank? I recall that they are powered open during refuelling. If they are closed and depowered in flight, presumably they are locked in position? They must also have a NRV in the out-of-tank direction only?
With such an inexplicable accident it is quite likely that two rare and non-related system failures have combined to produce the engine power loss, so bear with me if I try to eliminate all possible ways in which air might reach the tank pump inlets ( given that there must have been 2 or more system failures for that to happen)
Thank you for the further information. How do the refuel valves function physically and where are they in the main (wing) tank? I recall that they are powered open during refuelling. If they are closed and depowered in flight, presumably they are locked in position? They must also have a NRV in the out-of-tank direction only?
With such an inexplicable accident it is quite likely that two rare and non-related system failures have combined to produce the engine power loss, so bear with me if I try to eliminate all possible ways in which air might reach the tank pump inlets ( given that there must have been 2 or more system failures for that to happen)
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The refuel valves are solenoid controlled from the refuel panel and they require fuel pressure to push them open. That fuel pressure is supplied by the pumper truck or when the aircraft is on the ground and you want to transfer fuel around, you can use boost pumps in the other tanks to move the fuel. Of course then, you need to open the defuel valve.
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Originally Posted by Green-dot
how much transmitting power (radiated field emission) would be required to make a 28 Vdc relay move from run to cutoff position?
The transmitting power would be dependent on how far away the transmitter is (inverse-square law and all that) and whether the transmitter is broadcast or directed-energy.
One needs to know how much energy is required to move the relay. This is not dependent merely on the voltage rating of the part, but on its specific design and manufacture and that of the system of which it is part. Then you have to guess what kind of transmitter you want to know about and where it might have been. Then you can figure out how much power it would have needed.
And then you have to figure out how it might actually achieve the action proposed. It is obviously not sufficient just to put the right amount of energy there - one needs to suggest a causal mechanism.
PBL
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Jet II Quote:
Originally Posted by PETTIFOGGER
Nevertheless, fuel flow was restricted.
has that been definitely established?
Originally Posted by PETTIFOGGER
Nevertheless, fuel flow was restricted.
has that been definitely established?
To state it was restricted is probably not the right term but it was inadequate.
Quote from PBL:
The transmitting power would be dependent on how far away the transmitter is (inverse-square law and all that) and whether the transmitter is broadcast or directed-energy.
[Unquote]
We also need to know the frequencies most likely to affect: (a) valve solenoids; (b) servos/motors; and (c) computers.
The transmitting power would be dependent on how far away the transmitter is (inverse-square law and all that) and whether the transmitter is broadcast or directed-energy.
[Unquote]
We also need to know the frequencies most likely to affect: (a) valve solenoids; (b) servos/motors; and (c) computers.
Paxing All Over The World
Chris Scott
As PBL says, that depends ... on its specific design and manufacture ... each solenoid or motor has it's own windings and it's susceptibility to interference will be directly related to where it is in the a/c, and the other components around it.
We also need to know the frequencies most likely to affect: (a) valve solenoids; (b) servos/motors; and (c) computers.
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I dont think that an EMI scenario where the RF field is sufficient to engergise or de-energise a 28 volt relay is likely. I have never seen any direct effect to an electromagnetic relay from significant RF fields from 2 - 2000 MHz.
Problems only start when the relay has a semiconductor drive circuit (either integrated in the relay or remote from it). With insufficient or defective decoupling and filtering unwanted operation can be caused down to a few Volts/metre at VHF/UHF frequencies. ie 3 or 4 orders of magnitude less than my experience above.
Problems only start when the relay has a semiconductor drive circuit (either integrated in the relay or remote from it). With insufficient or defective decoupling and filtering unwanted operation can be caused down to a few Volts/metre at VHF/UHF frequencies. ie 3 or 4 orders of magnitude less than my experience above.
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Correct response - wrong circumstance
Warning: I'm non-professional; not crew, not engineer - just guest here, thanks.
In an earlier post I asked the following but no one has answered. Can anyone assist?
"An article on smartcockpit, written by an Airbus employee about Low Fuel Temperatures, has a table listing the Minimum Inlet Temperatures for engines from various manufacturers. RR has temp of 3C (This figure seems generalised for RR).
What happens next if the fuel heat exchange systems cannot raise the fuel temperature to, or above, 3C?"
I'm interested in the answer because:
1) as far as I have read, no one on the thread has explicitly discussed the systems designed to protect the engines in the event that fuel quality/quantity is below operating standard.
2) I also wonder if there has been a failure in applied logic, meaning, the aircraft systems did exactly what they were designed to do but under the wrong, or unforeseen, circumstances, namely in this case, about to land.
3) It's intriguing to me that some form of self-limiting system operated to reduce the engine speed to just above flight idle. Presumably (?) all of the ways in which an engine can be throttled back are fully known, that the actions are 'programmed' and follow some logic pathways developed during the design stage of the engines/aircraft. If so, the examination of the cause of incident would start by examining these logic pathways and associated systems. Of course, I'm assuming that an engine is never, under any circumstances, allowed to be un-controlled unless there has been some catastrophic failure.
And so, combining 1 to 3 above, and while reading about the 3C minimum fuel temperature, I wondered what the engines are designed to do under such circumstances. Leaving aside the provisions made for starting engines on the ground in freezing conditions, under what other conditions would designers have reasoned an aircraft’s fuel would be about to enter the engines below 3C and what should the engines do to protect themselves and the aircraft?
Could it be that the designers thought that those conditions are ‘only’ to be met at high altitude in very cold air, in which case, the best option is to command the engines to throttle back, to protect themselves, and force the aircraft to descend to warmer air?
But, suppose fuel below 3C was about to enter the engines on flight BA038 at very low altitude; what would the engines do?
You see my point – planned/designed response but wrong circumstances!
By the way, I’ve discussed the 3C temp. issue because that is what triggered my thoughts but you engineer types can probably think of other issues. But the issue must result in some system commanding a throttle back.
Okay, heading for bunker ….
Thanks in advance.
Regards, Tanimbar
In an earlier post I asked the following but no one has answered. Can anyone assist?
"An article on smartcockpit, written by an Airbus employee about Low Fuel Temperatures, has a table listing the Minimum Inlet Temperatures for engines from various manufacturers. RR has temp of 3C (This figure seems generalised for RR).
What happens next if the fuel heat exchange systems cannot raise the fuel temperature to, or above, 3C?"
I'm interested in the answer because:
1) as far as I have read, no one on the thread has explicitly discussed the systems designed to protect the engines in the event that fuel quality/quantity is below operating standard.
2) I also wonder if there has been a failure in applied logic, meaning, the aircraft systems did exactly what they were designed to do but under the wrong, or unforeseen, circumstances, namely in this case, about to land.
3) It's intriguing to me that some form of self-limiting system operated to reduce the engine speed to just above flight idle. Presumably (?) all of the ways in which an engine can be throttled back are fully known, that the actions are 'programmed' and follow some logic pathways developed during the design stage of the engines/aircraft. If so, the examination of the cause of incident would start by examining these logic pathways and associated systems. Of course, I'm assuming that an engine is never, under any circumstances, allowed to be un-controlled unless there has been some catastrophic failure.
And so, combining 1 to 3 above, and while reading about the 3C minimum fuel temperature, I wondered what the engines are designed to do under such circumstances. Leaving aside the provisions made for starting engines on the ground in freezing conditions, under what other conditions would designers have reasoned an aircraft’s fuel would be about to enter the engines below 3C and what should the engines do to protect themselves and the aircraft?
Could it be that the designers thought that those conditions are ‘only’ to be met at high altitude in very cold air, in which case, the best option is to command the engines to throttle back, to protect themselves, and force the aircraft to descend to warmer air?
But, suppose fuel below 3C was about to enter the engines on flight BA038 at very low altitude; what would the engines do?
You see my point – planned/designed response but wrong circumstances!
By the way, I’ve discussed the 3C temp. issue because that is what triggered my thoughts but you engineer types can probably think of other issues. But the issue must result in some system commanding a throttle back.
Okay, heading for bunker ….
Thanks in advance.
Regards, Tanimbar
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Vacuum in tank + rising outside pressure = fuel backflow?
When I read about the cavitation evidence in the fuel pumps, I immediately wondered if maybe a vacuum had built up in the fuel tanks, for example because the vent valve (used to let air enter the tanks as needed) might have been stuck.
A vacuum in the fuel tanks, combined with rising outside ambient pressure (plane approaching sea level), might ultimately lead to air bubbling backwards from the engine through the pumps and into the tanks - or not?
Two factors may have precipitated this condition exactly during the landing approach: The first factor being the ever increasing outside air pressure; and the second factor being that the engines were temporarily put into idle, presumably also reducing the pressure in the fuel supply pumps, which then would be more vulnerable to air flowing backwards than they were during cruise.
Once air starts flowing backwards through the pumps, they probably would not recover for quite a while.
A vacuum in the fuel tanks, combined with rising outside ambient pressure (plane approaching sea level), might ultimately lead to air bubbling backwards from the engine through the pumps and into the tanks - or not?
Two factors may have precipitated this condition exactly during the landing approach: The first factor being the ever increasing outside air pressure; and the second factor being that the engines were temporarily put into idle, presumably also reducing the pressure in the fuel supply pumps, which then would be more vulnerable to air flowing backwards than they were during cruise.
Once air starts flowing backwards through the pumps, they probably would not recover for quite a while.
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To follow up on Chris Scott's query and ionagh's reply, here are a few links from twenty years ago to problems the US Army may have had with EMI affecting its Black Hawk helicopters (I emphasise the words "may have had", in contrast to "did have"!). The Navy apparently did not have similar concerns with its Sea Hawks: they were better shielded because of the extremely EM-loud shipboard environment.
All from the Risks Digest:
From Risks 5.56
From Risks 5.58
Also from Risks 5.58
From Risks 5.59
From Risks 5.60
and a cautionary note from me:
in Risks 5.59
PBL
All from the Risks Digest:
From Risks 5.56
From Risks 5.58
Also from Risks 5.58
From Risks 5.59
From Risks 5.60
and a cautionary note from me:
in Risks 5.59
PBL
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Quote:
Originally Posted by Green-dot
how much transmitting power (radiated field emission) would be required to make a 28 Vdc relay move from run to cutoff position?
"The question is not well formulated."
PBL, i agree but you clearly filled in the blanks. Thanks for your clear explanation regarding a complex matter in such few words.
Regards,
Green-dot
Originally Posted by Green-dot
how much transmitting power (radiated field emission) would be required to make a 28 Vdc relay move from run to cutoff position?
"The question is not well formulated."
PBL, i agree but you clearly filled in the blanks. Thanks for your clear explanation regarding a complex matter in such few words.
Regards,
Green-dot
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...I need more popcorn...
Firstly, congrats to everyone (including me 
) that read through more than 2000 posts in this and previous threads...
Secondly, thanks to all the posters (and/or mods) for keeping this latest thread very much to the point as well as exceptionally "civilised" compared to previous ones.
I am starting with my 777 conversion in May this year and I will probably not have to study anything on the fuel system
- thanks for all those enlightening us with technical specs (be it 777 or not).
I do not want to speculate on this incident - not because I have anything against speculation, but because I just cannot think what could possibly cause this!
However, to all those with theories involving multiple failures / unlikely events; I think you might be on the right track.
This incident was completely out of the ordinary and very unlikely. Therefore one could expect something unthinkable to go wrong.
If it was a simple answer, we would have had it by now.
Regards
PP
...now where did I stash that popcorn again?
) that read through more than 2000 posts in this and previous threads...Secondly, thanks to all the posters (and/or mods) for keeping this latest thread very much to the point as well as exceptionally "civilised" compared to previous ones.
I am starting with my 777 conversion in May this year and I will probably not have to study anything on the fuel system
- thanks for all those enlightening us with technical specs (be it 777 or not).I do not want to speculate on this incident - not because I have anything against speculation, but because I just cannot think what could possibly cause this!
However, to all those with theories involving multiple failures / unlikely events; I think you might be on the right track.
This incident was completely out of the ordinary and very unlikely. Therefore one could expect something unthinkable to go wrong.
If it was a simple answer, we would have had it by now.
Regards
PP
...now where did I stash that popcorn again?
Last edited by Pitot Probe; 28th Feb 2008 at 20:19. Reason: typo
Gustep and all of the other "Vacuum/Blocked vent" theorists, there is a "low fuel pressure" warning that would no doubt have been triggered (and recorded) should this have occurred.
tanimbar
Would a system commanding a throttle back send the command to the EECs? As I understand it, the EECs reacted to a physical reduction in fuel flow, not a throttle back signal.
Would a system commanding a throttle back send the command to the EECs? As I understand it, the EECs reacted to a physical reduction in fuel flow, not a throttle back signal.