BA038 (B777) Thread
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At first si
Need to correct you. The DIFFERENCE between LH and RH installation was only 1 sec.
Roll back occurred after 7 or 8 secs.
Sorry if 7/89 looked like a fraction.
ght the 7 or 8 seconds difference could have been explained by a single fuel source going through a fuel crossfeed valve ...
Roll back occurred after 7 or 8 secs.
Sorry if 7/89 looked like a fraction.
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Hate to correct a correction, but according to the AAIB the difference was around 7 seconds, not only 1 sec:
However, at a height
of about 720 ft the thrust of the right engine reduced to approximately 1.03 EPR (engine pressure ratio); some seven seconds later the thrust on the left engine reduced
in addition to any asymmetry in the fuel feed geometry (possibility mentioned recently), there are other asymmetries which might possibly be relevant when looking at this difference. eg. Fuel levels were not identical in each wing (300kg difference I recall), and also one wing would have been in sun and the other in shade, therefore likely to be some temparature difference.
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A little more on resonance
ChristiaanJ
As the troublemaker who suggested resonance a few pages back I would have to agree with you that ‘As an explanation ...it seems somewhat far fetched’. However it seems whatever is finally determined as the cause of this fascinating problem is going to be something quite out of the ordinary given that this is still apparently eluding every attempt at exposure by the amassed genius of the AAIB, Boeing and PPrune correspondents to mention but a few!
Your further statement ‘…any “fuel hammer” effect is nearly instantaneous…’ is however absolutely untrue and very misleading.
Lomapaseo
In order for resonance to occur within the fuel system, I suggest that there is not one simple explanation that will satisfy the enquiry ‘But what is the forcing function and the response’ beyond the observation that there are pumps providing energy to a flexible structure (pipework and fuel) that includes non return valves which in certain very unusual and very undesired circumstances have the potential to block the flow of fuel as well as to more normally allow it to pass.
It is the (very unusual) specific combination of many different factors within the above, each itself within normal parameters that could lead to the system malfunctioning as described in my earlier post.
Barit1
If this resonance did occur and was enough to restrict the fuel flow, the frequency has to be in a range that will include the possibility of the non return valves being able to oscillate between a closed and probably fully open position. I would reckon this to be somewhat less than 10Hz but in any case far less than the likely frequency of the gear teeth meshing of the HP pump.
A far more likely source of would be the airframe vibration that is typically experienced in a final approach with plenty of flap and low airspeed. Even so, it is only the effect of this combined with the specific combination of other factors that – perhaps – could result in the fuel system going into this rather inconvenient state of malfunction.
Flight Safety
If a system such as this did go into a state of resonance, while the fuel demand remained low, adequate flow was apparently anyway maintained. Increasing the fuel demand in this circumstance however would exacerbate the difference in pressure on either side of the non return valves causing either or both the amplitude and frequency of oscillations to increase but the fuel flow to decrease as an ever increasing amount of the energy supplied by the pumps is absorbed in accelerating and de-accelerating the column of fuel within the pipes, generating shock waves and in accordance with Newton’s 3rd law, powering the reactive movements of the mass of fuel line, components and other connected structures.
As this situation developed, it is also of course very possible that the rapid changes of pressure and depression may have begun to release trapped vapours from the fuel which then begin to foam causing a further sequence of effects that have been discussed in previous posts.
The known end result is that whatever the reason, very little of the oily stuff got to the burners of the engine.
Regards to all!
JG
As the troublemaker who suggested resonance a few pages back I would have to agree with you that ‘As an explanation ...it seems somewhat far fetched’. However it seems whatever is finally determined as the cause of this fascinating problem is going to be something quite out of the ordinary given that this is still apparently eluding every attempt at exposure by the amassed genius of the AAIB, Boeing and PPrune correspondents to mention but a few!
Your further statement ‘…any “fuel hammer” effect is nearly instantaneous…’ is however absolutely untrue and very misleading.
Lomapaseo
In order for resonance to occur within the fuel system, I suggest that there is not one simple explanation that will satisfy the enquiry ‘But what is the forcing function and the response’ beyond the observation that there are pumps providing energy to a flexible structure (pipework and fuel) that includes non return valves which in certain very unusual and very undesired circumstances have the potential to block the flow of fuel as well as to more normally allow it to pass.
It is the (very unusual) specific combination of many different factors within the above, each itself within normal parameters that could lead to the system malfunctioning as described in my earlier post.
Barit1
If this resonance did occur and was enough to restrict the fuel flow, the frequency has to be in a range that will include the possibility of the non return valves being able to oscillate between a closed and probably fully open position. I would reckon this to be somewhat less than 10Hz but in any case far less than the likely frequency of the gear teeth meshing of the HP pump.
A far more likely source of would be the airframe vibration that is typically experienced in a final approach with plenty of flap and low airspeed. Even so, it is only the effect of this combined with the specific combination of other factors that – perhaps – could result in the fuel system going into this rather inconvenient state of malfunction.
Flight Safety
If a system such as this did go into a state of resonance, while the fuel demand remained low, adequate flow was apparently anyway maintained. Increasing the fuel demand in this circumstance however would exacerbate the difference in pressure on either side of the non return valves causing either or both the amplitude and frequency of oscillations to increase but the fuel flow to decrease as an ever increasing amount of the energy supplied by the pumps is absorbed in accelerating and de-accelerating the column of fuel within the pipes, generating shock waves and in accordance with Newton’s 3rd law, powering the reactive movements of the mass of fuel line, components and other connected structures.
As this situation developed, it is also of course very possible that the rapid changes of pressure and depression may have begun to release trapped vapours from the fuel which then begin to foam causing a further sequence of effects that have been discussed in previous posts.
The known end result is that whatever the reason, very little of the oily stuff got to the burners of the engine.
Regards to all!
JG
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To Joetom,
A spar valve in a position between open and closed most likely would have resulted in a (LH/RH) spar valve (actuator) disagree EICAS message when the actuator is not in the commanded position. A not fully open engine fuel shutoff valve would have been detected by the EEC.
Even in the very unlikely case faults would not have been detected, the most likely moment either of these valves would have malfunctioned is during engine start, the only time they are operated until they are closed at moment of engine shutdown. Both LH and RH side failing at the same time although not impossible, it is very remote.
During a normal engine (auto) start, the spar valves are opened manually by the fuel control switches and engine fuel shutoff valves are controlled by the EECs. Although the fuel control switches are manually selected from cutoff to run position, the timing of engine fuel valve opening is controlled by the EEC, it keeps the valve closed until the engine reaches the appropriate speed.
If the valves were only partially open, and if (in the unlikely event) faults were not detected by the EECs during engine start, the problems would have certainly surfaced during the takeoff roll when fuel flow is increased to meet takeoff thrust demand, a much higher demand than the thrust adjustments during final approach. A scenario for both spar valves to move away from commanded (open) position during cruise or approach has been discussed several times in this thread. Lack of evidence as to how this could have occurred prevents that discussion from continuing at this time.
Green-dot
Fuel flow could have been restricted for a long period of time.
Think of Spar or LP valve being in a position between open and closed, Engine will run Ok upto a point, but when FMV/FMU needs more flow than avail, problems will start, problems may be delayed a little with the head of fuel down stream of restriction, but problems on the way.
Think of Spar or LP valve being in a position between open and closed, Engine will run Ok upto a point, but when FMV/FMU needs more flow than avail, problems will start, problems may be delayed a little with the head of fuel down stream of restriction, but problems on the way.
Even in the very unlikely case faults would not have been detected, the most likely moment either of these valves would have malfunctioned is during engine start, the only time they are operated until they are closed at moment of engine shutdown. Both LH and RH side failing at the same time although not impossible, it is very remote.
During a normal engine (auto) start, the spar valves are opened manually by the fuel control switches and engine fuel shutoff valves are controlled by the EECs. Although the fuel control switches are manually selected from cutoff to run position, the timing of engine fuel valve opening is controlled by the EEC, it keeps the valve closed until the engine reaches the appropriate speed.
If the valves were only partially open, and if (in the unlikely event) faults were not detected by the EECs during engine start, the problems would have certainly surfaced during the takeoff roll when fuel flow is increased to meet takeoff thrust demand, a much higher demand than the thrust adjustments during final approach. A scenario for both spar valves to move away from commanded (open) position during cruise or approach has been discussed several times in this thread. Lack of evidence as to how this could have occurred prevents that discussion from continuing at this time.
Green-dot
Last edited by Green-dot; 16th Jun 2008 at 21:46. Reason: Clarifying the text
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the problems would have certainly surfaced during the takeoff roll when fuel flow is increased to meet takeoff thrust demand, a much higher demand than the thrust adjustments during final approach
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Originally Posted by johngreen"
ChristiaanJ
Your further statement ‘…any “fuel hammer” effect is nearly instantaneous…’ is however absolutely untrue and very misleading.
Your further statement ‘…any “fuel hammer” effect is nearly instantaneous…’ is however absolutely untrue and very misleading.
Although... I remember the F-14A prototype went down due to a similar (hydraulic system) failure on its second flight, not after x million flights/landings.
I'm still baffled by the number of holes in the cheese having to line up for this to happen for the first time.
I'm still baffled by the number of holes in the cheese having to line up for this to happen for the first time.
In this case the temperature at start-up for the return flight was below zero. If the fuel loaded was also below zero, there would be no water scavenge on take-off or climb out. The next opportunity for water to be scavenged from the centre tank would be aftert the descent to warmer levels, at which time it would be scavenged to the still cold wing tanks. Getting the holes to line up is not a problem - in fact it is a bit too easy, suggesting the holes are not big enough to bring an aircraft down.
For my money, the big question is how unusual is the history not just of that one flight, but of the history including the one before it and the conditions on the ground between the flights.
The cavitation damage statistics will be interesting. Any cavitation damage needs to be explained, because it is evidence of a fuel flow restriction at some stage of some flight. The fact that such damage is not unique to this aircraft might suggest that in this case there was just one hole too many, or the holes stayed lined up for just a few minutes too long.
The full explanation of the incident may well involve a long chain of coincidences involving more than one flight, and the investigation may take longer than usual as the correspondingly large number of alternative explanations are eliminated.
But there was no evidence of excess water in the fuel samples recovered ....
One value of different speculations about how an accident could have happened, is that it heightens awareness of how different accidents could happen.
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To Green Dot,
My last post only mentioned Spar Valves as an example of how a problem can exist and fuel flow through the FMU/FMV can appear normal until it causes a flow short fall. I would not expect Spar Valves to be the problem in this case, but they have caused low flow during engine operations, and yes I know EICAS/ECAM will give this info to the crew all things being normal.
My last post was just to point out that a problem/failure mode could have been lurking about long before the 38 reached Heathrow.
I'm still holding out for 1 or 2 reasons for the events on that day.
Reason 1. Leak on a fuel manifold.
Reason 2. CWT scavenged fluid into wings that had very cold fluid in them.
Both the above could start a chain of events that may fit.
The interesting points I remember are.
1. Aircraft had a cold flight to PEK.
2. Aircraft had a cold 3 hour transit in PEK.
3. Aircraft topped up wings with fuel in PEK.
4. Aircraft uplifted neat PEK fuel into CWT.
5. Aircraft had a cold flight to LHR.
6. Aircraft had little or no holding into LHR.
7. Aircraft engines wanted more flow, but was unable to provide.
Be kind to me, I'm tired !!!
My last post only mentioned Spar Valves as an example of how a problem can exist and fuel flow through the FMU/FMV can appear normal until it causes a flow short fall. I would not expect Spar Valves to be the problem in this case, but they have caused low flow during engine operations, and yes I know EICAS/ECAM will give this info to the crew all things being normal.
My last post was just to point out that a problem/failure mode could have been lurking about long before the 38 reached Heathrow.
I'm still holding out for 1 or 2 reasons for the events on that day.
Reason 1. Leak on a fuel manifold.
Reason 2. CWT scavenged fluid into wings that had very cold fluid in them.
Both the above could start a chain of events that may fit.
The interesting points I remember are.
1. Aircraft had a cold flight to PEK.
2. Aircraft had a cold 3 hour transit in PEK.
3. Aircraft topped up wings with fuel in PEK.
4. Aircraft uplifted neat PEK fuel into CWT.
5. Aircraft had a cold flight to LHR.
6. Aircraft had little or no holding into LHR.
7. Aircraft engines wanted more flow, but was unable to provide.
Be kind to me, I'm tired !!!
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Resonance
I'm not sure I see how resonance could be set up (or sustained) in this system.
First, the fuel was cold and viscous to some degree. The non return valve is one way, thus tending to cancel any resonance (which is oscillatory in nature). Resonance requires a sustained oscillation with feedback loop, and in a system that normally would not excite resonance, if one were to form under certain specific conditions, it should be easy to break up the resonance with some applied external force. Just to remind you, there were operating boost pumps and operating HP pumps here, with one at one end of the fuel "column" and one at the other end. I would think the forces of the pumps should tend to break up any resonances that might form.
I think this applies so long as a major structure(s) does not provide the feedback mechanism, which would be harder to overcome by external forces. If major structure(s) contributed to the feedback loop, then the system would display natural resonance quite readily.
I also seem to recall discussion that the non return valve is in the suction feed flow path and not in the boost pump flow path.
Water hammer (or fuel hammer) is just a pressure spike created when a valve opens or closes (due to column momentum) and is not really relavent here I would think. Water hammer (or fuel hammer) does not normally restrict flow, but is rather a design consideration pertaining to maximum pressures seen by the system.
I stand to be corrected of course.
First, the fuel was cold and viscous to some degree. The non return valve is one way, thus tending to cancel any resonance (which is oscillatory in nature). Resonance requires a sustained oscillation with feedback loop, and in a system that normally would not excite resonance, if one were to form under certain specific conditions, it should be easy to break up the resonance with some applied external force. Just to remind you, there were operating boost pumps and operating HP pumps here, with one at one end of the fuel "column" and one at the other end. I would think the forces of the pumps should tend to break up any resonances that might form.
I think this applies so long as a major structure(s) does not provide the feedback mechanism, which would be harder to overcome by external forces. If major structure(s) contributed to the feedback loop, then the system would display natural resonance quite readily.
I also seem to recall discussion that the non return valve is in the suction feed flow path and not in the boost pump flow path.
Water hammer (or fuel hammer) is just a pressure spike created when a valve opens or closes (due to column momentum) and is not really relavent here I would think. Water hammer (or fuel hammer) does not normally restrict flow, but is rather a design consideration pertaining to maximum pressures seen by the system.
I stand to be corrected of course.
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"The Non Return Valve Is One Way"
Not so. The function of the valve is to prevent "backflow" of the Fuel once it has passed the valve on its way to the Engine. The Valve sleeve moves in two directions, with flow (and against a spring), and versus flow, with the aid of the spring and the "backflow" of the Fuel, when it closes and prevents Fuel return. The mechanical "stop" can stall in any position, while transiting in either direction, vibrate (resonate) and completely stop Fuel entry into the system. All that is required (unlikely) is sufficient tuned energy to overcome the normal working parameters of the device.
I think some folks are visualizing the dynamic A/C system on short final without considering (perhaps) the level of energy and activity involved in landing 200 tons of incredibly powerful A/C full of PE and engines capable of lifting same. I remember my first experience watching the debut of PanAms first 747 in Honolulu. Relaxing on the beach at Sandy, about two miles from departure end, the A/C lumbered into the air "slowly". What dazzled everyone present was the sound. Everything shook from that spooky rumbling earthquake noise from the fans. the sand was vibrating on the beach.
Each of the RR engines has a fan that is probably too big to fit in one's garage, a device that can move air at a prodigious rate. Imagine each fan straining for purchase at full go, each Blade passing within a foot of the circular Fuel line around the shroud, inches from the Heat exchanger, and trying to disintegrate the HP pump. Feedback? The cold viscous Fuel in the Manifold has to resist carrying that energy throughout the system and still maintain flow within safe parameters. Resonance is definitely possible, and could easily occur given the right links in the chain. IMO.
In opposition people merely say, "Well, it never happened before."
Airfoil
"Ram". Resonance doesn't involve alot of "oscillation" My picture of Resonating fluid is a stalled stand (head), vibrating, rather asymmetrically relative to the "container". John Green might help us here.
I think some folks are visualizing the dynamic A/C system on short final without considering (perhaps) the level of energy and activity involved in landing 200 tons of incredibly powerful A/C full of PE and engines capable of lifting same. I remember my first experience watching the debut of PanAms first 747 in Honolulu. Relaxing on the beach at Sandy, about two miles from departure end, the A/C lumbered into the air "slowly". What dazzled everyone present was the sound. Everything shook from that spooky rumbling earthquake noise from the fans. the sand was vibrating on the beach.
Each of the RR engines has a fan that is probably too big to fit in one's garage, a device that can move air at a prodigious rate. Imagine each fan straining for purchase at full go, each Blade passing within a foot of the circular Fuel line around the shroud, inches from the Heat exchanger, and trying to disintegrate the HP pump. Feedback? The cold viscous Fuel in the Manifold has to resist carrying that energy throughout the system and still maintain flow within safe parameters. Resonance is definitely possible, and could easily occur given the right links in the chain. IMO.
In opposition people merely say, "Well, it never happened before."
Airfoil
"Ram". Resonance doesn't involve alot of "oscillation" My picture of Resonating fluid is a stalled stand (head), vibrating, rather asymmetrically relative to the "container". John Green might help us here.
Last edited by airfoilmod; 17th Jun 2008 at 14:28.
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Quoting Joetom,
With regards to reason 1:
A leak in the fuel manifold does not explain 2 engines rolling back within 8 seconds from eachother with crossfeed valves closed and an empty center tank.
With regards to reason 2:
According to the AAIB in their bulletin S1/2008 the aircraft's fuel tanks were last checked for water in the fuel on january 15 at Heathrow; this was prior to its refuelling for the sector to Beijing. Minimum temperature at Heathrow on January 15 was 6 deg. C, maximum temp. was 10 deg. C (I have temp. records for that day).
Warm enough to drain any water collected in the tanks if transit time was long enough between the previous flight and departure to Beijing. Since fuel samples taken after the accident revealed no excessive water content, it votes for correct water sampling on January 15th and that there was no significant amount of water in the tanks when departing for PEK.
So the flight to PEK may have been cold but if the tanks were "clean" with regards to water content when departing from Heathrow, steps 2 thru 7 become less relevant.
Regards,
Green-dot
I'm still holding out for 1 or 2 reasons for the events on that day.
Reason 1. Leak on a fuel manifold.
Reason 2. CWT scavenged fluid into wings that had very cold fluid in them.
Both the above could start a chain of events that may fit.
The interesting points I remember are.
1. Aircraft had a cold flight to PEK.
2. Aircraft had a cold 3 hour transit in PEK.
3. Aircraft topped up wings with fuel in PEK.
4. Aircraft uplifted neat PEK fuel into CWT.
5. Aircraft had a cold flight to LHR.
6. Aircraft had little or no holding into LHR.
7. Aircraft engines wanted more flow, but was unable to provide.
Reason 1. Leak on a fuel manifold.
Reason 2. CWT scavenged fluid into wings that had very cold fluid in them.
Both the above could start a chain of events that may fit.
The interesting points I remember are.
1. Aircraft had a cold flight to PEK.
2. Aircraft had a cold 3 hour transit in PEK.
3. Aircraft topped up wings with fuel in PEK.
4. Aircraft uplifted neat PEK fuel into CWT.
5. Aircraft had a cold flight to LHR.
6. Aircraft had little or no holding into LHR.
7. Aircraft engines wanted more flow, but was unable to provide.
A leak in the fuel manifold does not explain 2 engines rolling back within 8 seconds from eachother with crossfeed valves closed and an empty center tank.
With regards to reason 2:
According to the AAIB in their bulletin S1/2008 the aircraft's fuel tanks were last checked for water in the fuel on january 15 at Heathrow; this was prior to its refuelling for the sector to Beijing. Minimum temperature at Heathrow on January 15 was 6 deg. C, maximum temp. was 10 deg. C (I have temp. records for that day).
Warm enough to drain any water collected in the tanks if transit time was long enough between the previous flight and departure to Beijing. Since fuel samples taken after the accident revealed no excessive water content, it votes for correct water sampling on January 15th and that there was no significant amount of water in the tanks when departing for PEK.
So the flight to PEK may have been cold but if the tanks were "clean" with regards to water content when departing from Heathrow, steps 2 thru 7 become less relevant.
Regards,
Green-dot
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Airfoilmod:
Got a picture (cross section) of these specific one way valves?
Is it correct that at BOTH ends of the travel of the "restricting device" that fuel is completely shut off?
I'm more familiar with valves (spherical ball on a conical seat etc) whereby only one end of the travel actual restricts the flow.The design specifically ensures that flow is unrestricted in the other direction.
Interesting (if correct).
Two INDEPENDENT valves responding at the same time to some form of resonance (both systems likely tuned differently)...Possible but WOW!
Worse odds than the lottery!
The Valve sleeve moves in two directions, with flow (and against a spring), and versus flow, with the aid of the spring and the "backflow" of the Fuel, when it closes and prevents Fuel return. The mechanical "stop" can stall in any position, while transiting in either direction, vibrate (resonate) and completely stop Fuel entry into the system. All that is required (unlikely) is sufficient tuned energy to overcome the normal working parameters of the device.
Is it correct that at BOTH ends of the travel of the "restricting device" that fuel is completely shut off?
I'm more familiar with valves (spherical ball on a conical seat etc) whereby only one end of the travel actual restricts the flow.The design specifically ensures that flow is unrestricted in the other direction.
Interesting (if correct).
Two INDEPENDENT valves responding at the same time to some form of resonance (both systems likely tuned differently)...Possible but WOW!
Worse odds than the lottery!
Fuel properties
I have been following this thread from day 1. One might think that my daily involvement in the aviation safety business would mean that I would rather do other things after work than read pprune forums. Sadly perhaps -- in terms of my lack of more productive things to do on many an evening -- I find these sorts of discussions interesting and energising, sometimes even motivating me to wander off into some obscure corner of the web for hours at a time researching topics that arise from these pages.
So, here’s my comment: Over the past few years I've been directly involved in the investigation of aviation accidents and incidents, both civil and military, in diverse parts of this globe. I am certainly no subject matter expert when it comes to fuels and fuel properties but several previous incidents (and a couple of accidents) keep worming their way into my thoughts when I think of this occurrence. The cases I’m talking about have this in common: Unpredicted or unexpected changes to the behaviour, consistency, lubricity, viscosity or dispersal characteristics of fuel – caused by FSII. (Contrary to what some have written FSII is not one specific chemical formulation but can be one of several compositions, including dipropylene glycol, glycerol formal, and DiEGME.) As many of you know, the amount (if any) of FSII in the fuel loaded in China could fall into a fairly wide spectrum and still be within specs.
In serving this ball into the pprune court, I expect (and would appreciate) comments and critique on the possibility of FSII being a factor.
Grizz
So, here’s my comment: Over the past few years I've been directly involved in the investigation of aviation accidents and incidents, both civil and military, in diverse parts of this globe. I am certainly no subject matter expert when it comes to fuels and fuel properties but several previous incidents (and a couple of accidents) keep worming their way into my thoughts when I think of this occurrence. The cases I’m talking about have this in common: Unpredicted or unexpected changes to the behaviour, consistency, lubricity, viscosity or dispersal characteristics of fuel – caused by FSII. (Contrary to what some have written FSII is not one specific chemical formulation but can be one of several compositions, including dipropylene glycol, glycerol formal, and DiEGME.) As many of you know, the amount (if any) of FSII in the fuel loaded in China could fall into a fairly wide spectrum and still be within specs.
In serving this ball into the pprune court, I expect (and would appreciate) comments and critique on the possibility of FSII being a factor.
Grizz
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grizzled
I'll look for my very old post re: Icing Inhibitors in the uplifted Fuel in Beijing. I remember suggesting Propylene Glycol, Ethanol, and Alkylates. There are some Fuel guys here and chemists too, they'll most likely be interested in your post
Airfoil
#126,#144
Airfoil
#126,#144
FSII, if present in the fuel, might be a factor. I dicussed it previously in #1292...
However, I seem to recall that in an answer to my post, someone pointed out that the fuel filters would be automatically bypassed in the event of flow restriction?
An interesting one, and possibly of relevance to BA038, is particulate contamination. This is measured by filtering some fuel, and weighing the particulates collected. An associated test (which forms part of the military spec) is filtration time, which specifies the maximum time for 1 US gallon to be vacuum-filtered. We have had numerous problems where anti-icing additives have been incompletely mixed, which for reasons we dont fully understand, cause difficulties in filtration. Obviously, filtration difficulties would impact on the flow of fuel through aircraft filters, and I would imagine that the effect would worsen with decreasing temperture. However, I have no idea if the subject fuel contained any FSII - chances are it didn't. I also don't know if the AAIB have had particulate contamination/filtration time checked as strictly speaking, the limits only apply at the point of manufacture. It would seem unlikely that they haven't checked this basic point however.
Keeping Danny in Sandwiches
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Am I right in thinking that this is a new bulletin from the AAIB
http://www.aaib.dft.gov.uk/cms_resou...MM%2006-08.pdf
http://www.aaib.dft.gov.uk/cms_resou...MM%2006-08.pdf
As an electrochemist I have spent much of my life trying to understand technical mysteries associated with various liquids and their specifications. Based on this, when I read in the latest AAIB bulletin that the fuel "in many respects exceeding the appropriate specification" I start to ask the following type of question:
Are there some components in the fuel which have secondary benefits which have not, so far, been fully realised? E.g. lubrication. If this might be the case, then concentrating on those possible benefits might be the key to the mystery.
Are there some components in the fuel which have secondary benefits which have not, so far, been fully realised? E.g. lubrication. If this might be the case, then concentrating on those possible benefits might be the key to the mystery.
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Update
I think the release updates info to include the recon of the Fuel system and to announce that Boeing are now looking for "abnormal combination of parameters." (Having found no one "hole")
It's important to reconsider that "exceeding spec." does not qualify a Fuel as "superior" in quality. It is an easy mistake to make, but "exceed" means "beyond" as well and includes a description including "poor", "misses the mark", and suggests that whatever is present in the fuel may be degrading its quality and performance.
An FP of -57C can be acquired merely by adding light molecules. Acetone freezes lower than kero, as do any number of easily added off spec matls.
It's important to reconsider that "exceeding spec." does not qualify a Fuel as "superior" in quality. It is an easy mistake to make, but "exceed" means "beyond" as well and includes a description including "poor", "misses the mark", and suggests that whatever is present in the fuel may be degrading its quality and performance.
An FP of -57C can be acquired merely by adding light molecules. Acetone freezes lower than kero, as do any number of easily added off spec matls.