BA038 (B777) Thread
From AAIB report:
The really interesting thing here is: how often has something similar to what happened to MMM occurred (restricted fuel flow) but gone unnoticed as the restriction was not severe enough to cause engine problems? Could it be that what the industry regards as 'safe' flight profiles are sometimes 'outside the envelope'? We know from this accident that there is little/no evidence left behind, so shouldn't expect too much from records of other flights.
This may not be a specific RR/Boeing problem and could possibly apply to large variety of turbine aircraft that are operated in a certain way...
No individual parameter from the flight of G‑YMMM
has been identified to be outside previous operating
experience. The analysis is concentrating on identifying
abnormal combinations of parameters
has been identified to be outside previous operating
experience. The analysis is concentrating on identifying
abnormal combinations of parameters
This may not be a specific RR/Boeing problem and could possibly apply to large variety of turbine aircraft that are operated in a certain way...
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An excellent, carefully crafted update from the AAIB.
So, since we are down to a transitory fuel flow reduction affecting both engine subsystems, brought on in conjunction with lower than typical fuel temps, I am at last compelled to point out the following:
Toothpaste:
http://www.nytimes.com/2007/06/02/us...nt&oref=slogin
Antibiotics:
In one instance, an antibiotic approved by Zheng’s agency killed at least 10 patients last year before it was taken off the market. Zheng Xiaoyu [took] bribes in cash and gifts worth more than $832,000 when he was director of the State Food and Drug Administration...The U.S. Food and Drug Administration also warned consumers not to buy or eat imported fish from China labeled as monkfish because it might actually be pufferfish, which contains a potentially deadly toxin called tetrodotoxin.The warning came days after three southern U.S. states banned imports of catfish from China because they contained traces of antibiotics the FDA says have never been approved for use in aquaculture.
http://www.msnbc.msn.com/id/18911849/
Dog food:
http://www.usatoday.com/money/indust...od-china_N.htm
Heparin:
Federal drug regulators believe that a contaminant detected in a crucial blood thinner that has caused 81 deaths was added deliberately, something the Food and Drug Administration has only hinted at previously.
“F.D.A.’s working hypothesis is that this was intentional contamination, but this is not yet proven,” Dr. Janet Woodcock, director of the Food and Drug Administration’s drug center, told the House Subcommittee on Oversight and Investigations in written testimony given Tuesday.
A third of the material in some batches of the thinner heparin were contaminants, “and it does strain one’s credulity to suggest that might have been done accidentally,” Dr. Woodcock said.
Two weeks ago, Food and Drug Commissioner Andrew C. von Eschenbach told a Senate subcommittee that the contamination was done “by virtue of economic fraud,”...
http://www.nytimes.com/2008/04/30/he...iberate&st=nyt
Lead paint:
http://www.chicagotribune.com/busine...,7866975.story
Electronic components:
http://www.news.com/8301-10784_3-994...l?tag=nefd.pop
Bolts and fasteners:
http://209.85.215.104/search?q=cache...ient=firefox-a
http://www.ebearing.com/counterfeit.htm
Golf clubs, car parts,books, prunes, razors, film, running shoes...
http://www.cbsnews.com/stories/2004/...in595875.shtml
Are we so naive that we don't think the Chinese would doctor up some fuel to pass all bench tests, but still not be quite what it seems?
I sure hope a full GC mass spec analysis is being run on the retained fuel samples.
So, since we are down to a transitory fuel flow reduction affecting both engine subsystems, brought on in conjunction with lower than typical fuel temps, I am at last compelled to point out the following:
Toothpaste:
Toothpaste counterfeited with poison:
Over the years, Chinese counterfeiters have found it profitable to substitute diethylene glycol for its chemical cousin, glycerin, which is usually more expensive.
Over the years, Chinese counterfeiters have found it profitable to substitute diethylene glycol for its chemical cousin, glycerin, which is usually more expensive.
Antibiotics:
China’s top drug regulator gets death sentence
In one instance, an antibiotic approved by Zheng’s agency killed at least 10 patients last year before it was taken off the market. Zheng Xiaoyu [took] bribes in cash and gifts worth more than $832,000 when he was director of the State Food and Drug Administration...The U.S. Food and Drug Administration also warned consumers not to buy or eat imported fish from China labeled as monkfish because it might actually be pufferfish, which contains a potentially deadly toxin called tetrodotoxin.The warning came days after three southern U.S. states banned imports of catfish from China because they contained traces of antibiotics the FDA says have never been approved for use in aquaculture.
Dog food:
Chinese authorities acknowledged for the first time that ingredients exported to make pet food contained a prohibited chemical, stepping up their probe of two Chinese companies' roles in one of the USA's largest animal-food recalls.
While pledging cooperation with U.S. authorities investigating the recall, the Chinese government in a statement Thursday also disputed that the chemical — melamine, which is used to make plastic — was responsible for harming pets.... "There is no clear evidence showing that melamine is the direct cause of the poisoning or death of the pets," the Ministry of Foreign Affairs in Beijing argued in a prepared statement.
While pledging cooperation with U.S. authorities investigating the recall, the Chinese government in a statement Thursday also disputed that the chemical — melamine, which is used to make plastic — was responsible for harming pets.... "There is no clear evidence showing that melamine is the direct cause of the poisoning or death of the pets," the Ministry of Foreign Affairs in Beijing argued in a prepared statement.
Heparin:
Federal drug regulators believe that a contaminant detected in a crucial blood thinner that has caused 81 deaths was added deliberately, something the Food and Drug Administration has only hinted at previously.
“F.D.A.’s working hypothesis is that this was intentional contamination, but this is not yet proven,” Dr. Janet Woodcock, director of the Food and Drug Administration’s drug center, told the House Subcommittee on Oversight and Investigations in written testimony given Tuesday.
A third of the material in some batches of the thinner heparin were contaminants, “and it does strain one’s credulity to suggest that might have been done accidentally,” Dr. Woodcock said.
Two weeks ago, Food and Drug Commissioner Andrew C. von Eschenbach told a Senate subcommittee that the contamination was done “by virtue of economic fraud,”...
Lead paint:
n 2007, the U.S. Consumer Product Safety Commission issued a recall of 1.5 million Thomas toys made in China because they contained unsafe amounts of lead paint.
Electronic components:
The FBI announced Friday that an investigation into counterfeit network components made in China and sold to the U.S. government has recovered about 3,500 fake devices with a value of $3.5 million. The criminal probe, code-named Operation Cisco Raider, was prompted by concerns that counterfeit network components could give hackers access to government databases.
Bolts and fasteners:
In 2003, more than 66% of goods seized at ports of entry into this country were traced to China. What are Counterfeiting and Piracy Costing the American Economy. National Chamber Foundation, 2005.
http://www.ebearing.com/counterfeit.htm
Golf clubs, car parts,books, prunes, razors, film, running shoes...
The World's Greatest Fakes
-Chinese Copies Are Making Their Way Back To U.S.
"We don't want to ignore counterfeiting, but for those foreign companies, when they enter the Chinese market, I'm afraid they should also pay some cost due to the realities of China," says Feng
Are we so naive that we don't think the Chinese would doctor up some fuel to pass all bench tests, but still not be quite what it seems?
I sure hope a full GC mass spec analysis is being run on the retained fuel samples.
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"How would you explain every other flight from PEK to Europe that night having no other issues with fuel?"
A quite reasonable question, of course. My best SPECULATIVE answer:
1) Their not having followed the same flight regime (including a host of environmental and operational factors)
2) Them not all being B-777, with perhaps a unique vulnerability in the piping configuration.
3) Their not having received the exact fuel load, from the same reservoir , that BA-038 got
In other HIGHLY SPECULATIVE words, I think that substandard fuel was probably a key factor, but one that needed one (or several) other elements to be in place in order to cause the response that occurred -- partial occlusion of the input lines to both HP fuel pumps during decent.
Again, a complete GC mass spec analysis should be cheap, easy, and definitive.
A quite reasonable question, of course. My best SPECULATIVE answer:
1) Their not having followed the same flight regime (including a host of environmental and operational factors)
2) Them not all being B-777, with perhaps a unique vulnerability in the piping configuration.
3) Their not having received the exact fuel load, from the same reservoir , that BA-038 got
In other HIGHLY SPECULATIVE words, I think that substandard fuel was probably a key factor, but one that needed one (or several) other elements to be in place in order to cause the response that occurred -- partial occlusion of the input lines to both HP fuel pumps during decent.
Again, a complete GC mass spec analysis should be cheap, easy, and definitive.
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Plumbing query
Where does the fuel for the APU come from? Is the supply from a specific tank; is it from any and all, with its own complex of valves and pumps; or is it take off the fed to one or both main engines? Does the pipework between the supply point and the APU pumps remain full at all times, or do the pipes drain during normal flight?
Hypothesis: if there are empty pipes leading to the APU, and the APU supply is taken from some point in the system downstream of the first pumps in the path to a main engine, then starting up the APU will cause a low-pressure transient in the supply system. The short term effect, possibly for a few seconds, would be for almost all fuel to take the path of least resistance and so starve the main engines.
I understand from some posts too far back to find easily that the APU start sequence was initiated before impact. Was it before of after the start of the final "glider" phase.
On a different sub-thread, would flying through and knocking down the boundary fence, rather than hopping over it, have had any significant effect on the outcome?
Hypothesis: if there are empty pipes leading to the APU, and the APU supply is taken from some point in the system downstream of the first pumps in the path to a main engine, then starting up the APU will cause a low-pressure transient in the supply system. The short term effect, possibly for a few seconds, would be for almost all fuel to take the path of least resistance and so starve the main engines.
I understand from some posts too far back to find easily that the APU start sequence was initiated before impact. Was it before of after the start of the final "glider" phase.
On a different sub-thread, would flying through and knocking down the boundary fence, rather than hopping over it, have had any significant effect on the outcome?
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Probably not. Raising the flaps got them over the fence and closer to the runway and probably kept the sink rate from increasing with the decrease in drag. The crew did everything right and probably the lesser sink rate on impact saved the day. Whatever they come up with as the reason for no throttle response, the pilots did everything they could, thinking outside the box, to get that 777 down the best way they could.
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Heathrow Crash caused by fuel freeze
WE are discussing this article and the interim report issued monday, may 12, 2008.
Heathrow crash landing 'caused by fuel freeze'
By David Millward, Transport Editor
Last Updated: 2:32AM BST 13/05/2008
The crash landing of a British Airways Boeing 777 at Heathrow may have been caused by abnormally cold conditions over Russia, air investigators have said.
Image**of*
REUTERS
Experts have homed in on fuel flow as the key issue which led to the crash landing of the Boeing 777
Flight BA38 was forced to make an emergency landing at Heathrow when it lost thrust in both engines at 600ft coming in to land on January 17.
Witnesses described seeing the airline bank sharply to the left and miss the tops of houses by 200ft as First Officer John Coward glided the aircraft to safety.
It missed the perimeter fence by inches before touching down on the grass, leaving one passenger seriously injured and 12 others slightly hurt.
Article continues
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On Monday, in an interim report, the Air Accident Investigations Branch (AAIB) said the drop in temperatures to -105F (-76C) may have caused the fuel in the aircraft to thicken during the flight which meant it was unable to get the additional thrust needed to land.
Further tests will be carried out to establish precisely what happened.
The circumstances leading to the worst aviation accident at Heathrow in more than 30 years will raise some concerns over the safety of the Boeing 777. However, neither Britain's safety regulators, Boeing, nor Rolls Royce, the engine's manufacturers, have recommended operational changes.
There are 667 Boeing 777s in service – with 40 in the British Airways fleet – and it is regarded as one of the safest airliners in the world. None has been lost since the plane first flew in 1995.
In its report the AAIB has focused on the "region of particularly cold air" between the Urals and Eastern Scandinavia during the 10-hour flight from Beijing to Heathrow.
It found that temperatures plummeted far lower than would have been expected for the region.
As a result, AAIB experts are examining what this would have done to the fuel and whether this would have caused a change in its consistency. Although the weather was unusually cold, it was not unprecedented and such problems have never been reported before.
The AAIB has established that the fuel used on the aircraft was of high quality.
While the average freezing temperature of aviation fuel is -53F (-47C), tests showed that the fuel used on the airliner does not turn to ice until -71F (-57C). Tests also found that the fuel temperature throughout the flight never dropped below -29F (-34C).
Even though the fuel did not become frozen it could have thickened to an unusual extent, which could have restricted its flow. Fresh tests on fuel are being carried out both at Rolls-Royce's engine plant in Derby and Boeing's factory in Seattle.
A number of other theories have been ruled out by the AAIB. They include birds flying into the engine or ice blocking the engine intake.
David Learmount, the operations and safety editor at Flight International, said all the evidence was starting to point towards the consistency of the fuel. "There might have been an issue with viscosity – with the fuel becoming thicker and flowing less well," he said.
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Heathrow crash landing 'caused by fuel freeze'
By David Millward, Transport Editor
Last Updated: 2:32AM BST 13/05/2008
The crash landing of a British Airways Boeing 777 at Heathrow may have been caused by abnormally cold conditions over Russia, air investigators have said.
Image**of*
REUTERS
Experts have homed in on fuel flow as the key issue which led to the crash landing of the Boeing 777
Flight BA38 was forced to make an emergency landing at Heathrow when it lost thrust in both engines at 600ft coming in to land on January 17.
Witnesses described seeing the airline bank sharply to the left and miss the tops of houses by 200ft as First Officer John Coward glided the aircraft to safety.
It missed the perimeter fence by inches before touching down on the grass, leaving one passenger seriously injured and 12 others slightly hurt.
Article continues
advertisement
On Monday, in an interim report, the Air Accident Investigations Branch (AAIB) said the drop in temperatures to -105F (-76C) may have caused the fuel in the aircraft to thicken during the flight which meant it was unable to get the additional thrust needed to land.
Further tests will be carried out to establish precisely what happened.
The circumstances leading to the worst aviation accident at Heathrow in more than 30 years will raise some concerns over the safety of the Boeing 777. However, neither Britain's safety regulators, Boeing, nor Rolls Royce, the engine's manufacturers, have recommended operational changes.
There are 667 Boeing 777s in service – with 40 in the British Airways fleet – and it is regarded as one of the safest airliners in the world. None has been lost since the plane first flew in 1995.
In its report the AAIB has focused on the "region of particularly cold air" between the Urals and Eastern Scandinavia during the 10-hour flight from Beijing to Heathrow.
It found that temperatures plummeted far lower than would have been expected for the region.
As a result, AAIB experts are examining what this would have done to the fuel and whether this would have caused a change in its consistency. Although the weather was unusually cold, it was not unprecedented and such problems have never been reported before.
The AAIB has established that the fuel used on the aircraft was of high quality.
While the average freezing temperature of aviation fuel is -53F (-47C), tests showed that the fuel used on the airliner does not turn to ice until -71F (-57C). Tests also found that the fuel temperature throughout the flight never dropped below -29F (-34C).
Even though the fuel did not become frozen it could have thickened to an unusual extent, which could have restricted its flow. Fresh tests on fuel are being carried out both at Rolls-Royce's engine plant in Derby and Boeing's factory in Seattle.
A number of other theories have been ruled out by the AAIB. They include birds flying into the engine or ice blocking the engine intake.
David Learmount, the operations and safety editor at Flight International, said all the evidence was starting to point towards the consistency of the fuel. "There might have been an issue with viscosity – with the fuel becoming thicker and flowing less well," he said.
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Is it possible for cold-soaked fuel to start depositing wax on the interior of fuel feed lines, in much the same way plaques gradually fur-up your arteries?
Just a thought that occurred - during the cruise phase, a high flow-rate may prevent this from happening. Throttle back for a descent, lower flow rate, less friction, lower velocity=higher effective pressure (iaw Bernouilli). Cold-soaked fuel may start building wax somewhere along the inside of a feed line, hence restriction. After the fact, wax buildup melts, evidence vanishes.
Just throwing a possibility out there - I'm sure somebody much more versed in fluid dynamics than I could critique (read - shoot down!) this theory.
Just a thought that occurred - during the cruise phase, a high flow-rate may prevent this from happening. Throttle back for a descent, lower flow rate, less friction, lower velocity=higher effective pressure (iaw Bernouilli). Cold-soaked fuel may start building wax somewhere along the inside of a feed line, hence restriction. After the fact, wax buildup melts, evidence vanishes.
Just throwing a possibility out there - I'm sure somebody much more versed in fluid dynamics than I could critique (read - shoot down!) this theory.
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Intermittent . . .?
Or it was something of an intermittent nature that was not recorded.
Either because something migrated but was restored before reaching a recording parameter. Or it was not on the list of recording parameters at all?
The AAIB states: "The spar valves and the aircraft fuel boost pumps were serviceable and operated correctly during the flight."
This would imply for the spar valves, to make the AAIB reach that conclusion, that both open and closed positions are continuously recorded and any migration from the open to the closed position but not reaching the closed position is also sensed and continuously, accurately recorded.
If so, then the spar valves are ruled out as suspect.
Green-dot
Either because something migrated but was restored before reaching a recording parameter. Or it was not on the list of recording parameters at all?
The AAIB states: "The spar valves and the aircraft fuel boost pumps were serviceable and operated correctly during the flight."
This would imply for the spar valves, to make the AAIB reach that conclusion, that both open and closed positions are continuously recorded and any migration from the open to the closed position but not reaching the closed position is also sensed and continuously, accurately recorded.
If so, then the spar valves are ruled out as suspect.
Green-dot
Last edited by Green-dot; 13th May 2008 at 20:12. Reason: Typo
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APU Fuel Path
The APU is fed from the left engine fuel manifold, which is supplied by either left boost pump (main tank aft, main tank forward, center tank left), or by an additional DC pump in the left main tank. When, as the AAIB said they did, the boost pumps are working, there is positive pressure in the fuel manifolds.
Starting up the APU (for which there is no evidence) would not lead to a sufficient pressure drop to starve the main engines. The APU fuel demand is tiny compared to the supply capacity of the boost pumps.
Bernd
Starting up the APU (for which there is no evidence) would not lead to a sufficient pressure drop to starve the main engines. The APU fuel demand is tiny compared to the supply capacity of the boost pumps.
Bernd
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Yet another idea!
The latest AAIB report has indeed focussed our understanding and has allowed different weighting to be applied to different potential scenarios.
Now the significant new bit of data (IMHO) is the similarity of the actual EPR at WOT (wide open throttle).
What could cause such similar limiting EPR on BOTH engine installations?
I believe we have to be talking of shortcoming in either Design Concept or more likely Standards. i.e. everything was within the agreed operating parameters which is why nothing untoward can be found.
I therefore make the following contention.
As fuel temp decreases its propensity to wax increases but this transition (I believe) is not clear cut being dependent upon the degree of molecular disturbance/agitation.
Now the fuel must have been flowing adequately to maintain cruise requirements which I assume would have been similar to that demanded during the ill fated finals.
However during the descent the reduced fuel demand at flight idle MAY have allowed already very cold fuel to transition to wax due to reduced molecular agitation.
This would fit with the indication from the AAIB that (low temperature?) flow testing is being undertaken.
In addition I have always been "suspicious" about the fuel.
Its wax point has been verified at -57C, a full 10 degrees better than specification. I keep asking. Why?
So maybe the fuel was within specification but does anybody have any idea how this test is conducted (i.e. Is the fuel placed (statically) in a vessel in a lab freezer or is the fuel agitated in someway during the test?)
I also remain surprised that no directive has been issued requiring a temporary tightening of minimum fuel temperature permissible.
I look forward to your response and further debate.
Now the significant new bit of data (IMHO) is the similarity of the actual EPR at WOT (wide open throttle).
What could cause such similar limiting EPR on BOTH engine installations?
I believe we have to be talking of shortcoming in either Design Concept or more likely Standards. i.e. everything was within the agreed operating parameters which is why nothing untoward can be found.
I therefore make the following contention.
As fuel temp decreases its propensity to wax increases but this transition (I believe) is not clear cut being dependent upon the degree of molecular disturbance/agitation.
Now the fuel must have been flowing adequately to maintain cruise requirements which I assume would have been similar to that demanded during the ill fated finals.
However during the descent the reduced fuel demand at flight idle MAY have allowed already very cold fuel to transition to wax due to reduced molecular agitation.
This would fit with the indication from the AAIB that (low temperature?) flow testing is being undertaken.
In addition I have always been "suspicious" about the fuel.
Its wax point has been verified at -57C, a full 10 degrees better than specification. I keep asking. Why?
So maybe the fuel was within specification but does anybody have any idea how this test is conducted (i.e. Is the fuel placed (statically) in a vessel in a lab freezer or is the fuel agitated in someway during the test?)
I also remain surprised that no directive has been issued requiring a temporary tightening of minimum fuel temperature permissible.
I look forward to your response and further debate.
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http://www.paclp.com/product/ISL/lit_isl/FZP%205G2s.pdf
"The freezing point of jet fuel is defined as the temperature at which the last crystal melts when warming a fuel that has been previously cooled until hyrdocarbon crystals form"
http://www.expotechusa.com/catalogs%...g/05-Fuels.pdf
Page 94
The sample is cooled in the test chamber with constantly stirring. The sophisticated dynamic measurement system emits a light pulse every 0.58C from a coaxial fiber optic cable positioned above the test sample. The light pulse is then reflected off the silvered-bottom test jar to an optical sensor. The advanced software package analyzes the response of the light pulse. The initial appearance of crystallization is monitored by light scattering. The sample is then warmed up, and the temperature at which the hydrocarbon crystals disappear is recorded as the freezing point.
"The freezing point of jet fuel is defined as the temperature at which the last crystal melts when warming a fuel that has been previously cooled until hyrdocarbon crystals form"
http://www.expotechusa.com/catalogs%...g/05-Fuels.pdf
Page 94
The sample is cooled in the test chamber with constantly stirring. The sophisticated dynamic measurement system emits a light pulse every 0.58C from a coaxial fiber optic cable positioned above the test sample. The light pulse is then reflected off the silvered-bottom test jar to an optical sensor. The advanced software package analyzes the response of the light pulse. The initial appearance of crystallization is monitored by light scattering. The sample is then warmed up, and the temperature at which the hydrocarbon crystals disappear is recorded as the freezing point.
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bsieker says (re May 12 report )
How does that follow? If fuel were foaming per earlier comments, measured flow would remain low, fuel energy would remain low, and a quick reversal of that condition would not be possible because foam encapsulated vapours would occupy some fair portion of the volume of the flow path, preventing immediate inflow of fuel, even if it were available (given that the foaming would have been caused or initiated by a blockage of some sort to begin with in the tank-HP pump path, and that blockage might well have continued) .
Please explain the logic of your dismissive comment.
- Flow stayed low after FMV was fully open (refuting "low-energy fuel" and "foaming fuel" theories)
Please explain the logic of your dismissive comment.
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Originally Posted by arcniz
Originally Posted by bsieker
- Flow stayed low after FMV was fully open (refuting "low-energy fuel" and "foaming fuel" theories)
Please explain the logic of your dismissive comment.
I assume the Fuel Flow Transmitter measures volume flow, and not mass flow.
I am also unsure foam would remain foamy in the high pressure conditions downstream of the HP pump.
Foam anywhere else, contributing to a fuel flow restriction, and allowing only a minor amount of (liquid) fuel to be pumped to the nozzles, would still be a possibility. I am not a fuel chemist, so I won't comment on the likelihood or mechanics of that.
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Mass Flow Transmitters
hetfield,
thanks a lot.
I've been reading up a little and it appears that due to the widely varying temperatures (I'd reasonably expect somewhere between +40 and -40 degrees C) and densities of jet fuel, mass-flow transmitters are commonly used, probably in RR engines, too. Energy content per mass unit is almost constant, but varies per volume unit, so that makes sense.
That would also mean that fuel foam at full volume flow would still register low (mass) fuel flow, contrary to my earlier comments.
Bernd
thanks a lot.
I've been reading up a little and it appears that due to the widely varying temperatures (I'd reasonably expect somewhere between +40 and -40 degrees C) and densities of jet fuel, mass-flow transmitters are commonly used, probably in RR engines, too. Energy content per mass unit is almost constant, but varies per volume unit, so that makes sense.
That would also mean that fuel foam at full volume flow would still register low (mass) fuel flow, contrary to my earlier comments.
Bernd
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Ref: Fuel freezing point, Actual vs Spec
A specification is set out by the purchaser or authority over an industry for any given chemical substance (including aviation fuel). The specification sets out for some parameters the lowest acceptable quality of the substance, and for other parameters the widest acceptable range. Having worked in the industrial chemical business for the past 14 years, I know it is not unusual for a chemical substance to be of a far higher standard than that set out on the Specification Sheet.
The reason the spec is put together this way is to allow for variations of product characteristics due to slight differences in manufacturing processes, slight differences in constituent products, slight differences in ambient conditions during the manufacturing processes and various other deviations during manufacture. Someone more familiar with the cracking of hydrocarbon fuels will no doubt provide the specifics of these variances and their corresponding tolerances within the spec.
In this instance, the lowest acceptable quality of the fuel is a freezing point of -47C, but the fuel itself has an actual freezing point of -57C (therefore it's quality is above spec). While this does not rule out the presence of a contaminant, it is certainly not a positive indicator of one.
The reason the spec is put together this way is to allow for variations of product characteristics due to slight differences in manufacturing processes, slight differences in constituent products, slight differences in ambient conditions during the manufacturing processes and various other deviations during manufacture. Someone more familiar with the cracking of hydrocarbon fuels will no doubt provide the specifics of these variances and their corresponding tolerances within the spec.
In this instance, the lowest acceptable quality of the fuel is a freezing point of -47C, but the fuel itself has an actual freezing point of -57C (therefore it's quality is above spec). While this does not rule out the presence of a contaminant, it is certainly not a positive indicator of one.
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Fuel waxing in cold temperatures
This may have no relevance to aviation fuel, however:
I lived in Germany for 25 years and during that time we had some extremely cold surface temperatures - I remember -27ºc on several occasions.
Having always driven diesel cars - from before the time when "winter grade diesel" was commonly available, I occasionally experienced waxing of fuel with consequent inability to start the car. The waxing either builds up in or causes blockage of the extremely small passages in the injector pump, at a time when fuel in the supply pipeline is still flowing easily.
The wax persists for long after the vehicle has been towed into a heated garage: the rule-of-thumb used to be 24hrs of heat-soak before trying to restart the car.
I lived in Germany for 25 years and during that time we had some extremely cold surface temperatures - I remember -27ºc on several occasions.
Having always driven diesel cars - from before the time when "winter grade diesel" was commonly available, I occasionally experienced waxing of fuel with consequent inability to start the car. The waxing either builds up in or causes blockage of the extremely small passages in the injector pump, at a time when fuel in the supply pipeline is still flowing easily.
The wax persists for long after the vehicle has been towed into a heated garage: the rule-of-thumb used to be 24hrs of heat-soak before trying to restart the car.
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The heat exchanger is the only part still being studied as a contributing cause, according to today's Washington Post.
http://www.washingtonpost.com/wp-dyn...1202728_2.html
But the recorders quickly disproved that theory, revealing no errors in the computer signals sent from the cockpit to the engines, according to reports and sources. Meanwhile, investigators were looking at the plane's fuel supply. An empty gas tank would have led to a thrust reduction, but the plane's tanks still contained plenty of high-quality fuel, investigators said in reports.
When they took apart the engines, investigators found evidence on pumps that the engines had been starved for fuel in the moments before the crash. That led them to conclude that the fuel supply had become blocked somewhere between the plane's tanks and its engines.
Sources familiar with the probe said engineers suspect that ice collected in or near a fuel-oil heat exchanger on each engine, blocking the fuel supply. The heat exchanger uses cold fuel to cool hot engine oil, and the hot engine oil to warm fuel before it is injected into the engines. The heat exchanger is the only point in the system that engineers have not yet eliminated as the potential bottleneck, the sources said.
But the ice theory is not perfect. Plenty of jets fly through cold weather, and the 777's fuel contained additives designed to prevent it from freezing under such conditions.
Outside experts noted that the ice theory seems implausible for another reason: Each engine should have been drawing fuel from a separate tank. The chances of ice breaking off in separate fuel tanks and blocking the fuel supply in each engine at nearly the same moment is almost too tiny to comprehend, said John Goglia, a former member at the National Transportation Safety Board, which investigates air crashes in the United States.
"This isn't supposed to happen," Goglia said. "These are two independent systems."
When they took apart the engines, investigators found evidence on pumps that the engines had been starved for fuel in the moments before the crash. That led them to conclude that the fuel supply had become blocked somewhere between the plane's tanks and its engines.
Sources familiar with the probe said engineers suspect that ice collected in or near a fuel-oil heat exchanger on each engine, blocking the fuel supply. The heat exchanger uses cold fuel to cool hot engine oil, and the hot engine oil to warm fuel before it is injected into the engines. The heat exchanger is the only point in the system that engineers have not yet eliminated as the potential bottleneck, the sources said.
But the ice theory is not perfect. Plenty of jets fly through cold weather, and the 777's fuel contained additives designed to prevent it from freezing under such conditions.
Outside experts noted that the ice theory seems implausible for another reason: Each engine should have been drawing fuel from a separate tank. The chances of ice breaking off in separate fuel tanks and blocking the fuel supply in each engine at nearly the same moment is almost too tiny to comprehend, said John Goglia, a former member at the National Transportation Safety Board, which investigates air crashes in the United States.
"This isn't supposed to happen," Goglia said. "These are two independent systems."