AAIB BA38 B777 Initial Report Update 23 January 2008
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I don't want to continue on the Boeing vs Airbus track but I remember that Airbus heats its fuel in the tank by pumping too much fuel to the engines, thus pressing the excessive warm fuel back into the outer tank where it warms up the remaining fuel there.
Doesn't Boeing have this feature? If you 747 driver talk about fuel temp alerts, do you have this with a similar kind of fuel warming or without?
I never flew Airbus widebody but I don't know of any incident or even a procedure in case of fuel temp too low. Anyone?
Dani
Doesn't Boeing have this feature? If you 747 driver talk about fuel temp alerts, do you have this with a similar kind of fuel warming or without?
I never flew Airbus widebody but I don't know of any incident or even a procedure in case of fuel temp too low. Anyone?
Dani
Nemo Me Impune Lacessit
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This is very basic but on the Boeing hot engine oil is passed, via lines, through cold fuel thus warming the fuel and cooling the oil.
Stillalbatross - From what I have read it is a Godsend that this 777 landed in the relatively soft undershoot and didn't make it to the runway hard surface.
Stillalbatross - From what I have read it is a Godsend that this 777 landed in the relatively soft undershoot and didn't make it to the runway hard surface.
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I remember that Airbus heats its fuel in the tank by pumping too much fuel to the engines, thus pressing the excessive warm fuel back into the outer tank where it warms up the remaining fuel there.
But it is a small amount of fuel and the effect is limited. I meet A319 that have flown over 6 hours, the fuel tank temp now is around M18degC.
but on the Boeing hot engine oil is passed, via lines, through cold fuel thus warming the fuel and cooling the oil.
I hope you are talking about in the engine. Engine oil does not leave the engine.
But it is a small amount of fuel and the effect is limited. I meet A319 that have flown over 6 hours, the fuel tank temp now is around M18degC.
but on the Boeing hot engine oil is passed, via lines, through cold fuel thus warming the fuel and cooling the oil.
I hope you are talking about in the engine. Engine oil does not leave the engine.
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Dani
The A330/A340 has the following caution FUEL FUEL LO TEMP
This caution appears, as soon as the inner tank temperature is less than —37°C, or outer or trim tank temperature is tess than -40 deg C. However, at this threshold: Crew action is required for JET A FUEL only, and no crew action is required for other fuel types.
For all other fuel types : This caution will automatically be recalled, if the temperature reaches - 44cC (inner tank temp), or —47°C (outer or trim tank temp). However, regardless of the fuel type, the crew may consider delaying application of the procedure, until reaching the minimum fuel temperature specific to their fuel type (Refer to 3.01.28, page 1).
• On ground, before takeoff:
• IF JET A:
DELAY T.O.
Do not takeoff until the temperature is within limits.
• In flight
• If inner tank temp is less than —37°C (auto recall at —44°C)
Crew awareness.
• If outer tank temp is less than —40°C (auto recall at —47°C)
• IF JET A (not displayed at —47°C)
— OUTER TK TFR . . . . . . . . . . . . . . . . . . . . . . ON
• If trim tank temp is less than —40°C (auto recall at —47°C)
• IF JET A (not displayed at —47°C)
— TRIM TANK .................................................ON
If the trim tank pump fails, this part of the procedure is replaced by:
WHEN SPD> 270 KT AND NOT IN CLIMB:
—T TANK MODE FWD
— Fuel consumption increases by approximately 7%.
• IF NECESSARY:
— TAT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . INCREASE
Consider descent to a lower altitude and/or increasing Mach to increase TAT
The temperatures shown are dependent on engine type but only vary by 1 or 2 degrees. There is also a fuel temperature prediction program offered by Airbus that will predict fuel temperature issues on a given flight route, aircraft type and current met data.
Personally given the flight phase this occured, I wouldnt have thought it would be fuel waxing issue but as with most I'm awaiting the accident report.
The A330/A340 has the following caution FUEL FUEL LO TEMP
This caution appears, as soon as the inner tank temperature is less than —37°C, or outer or trim tank temperature is tess than -40 deg C. However, at this threshold: Crew action is required for JET A FUEL only, and no crew action is required for other fuel types.
For all other fuel types : This caution will automatically be recalled, if the temperature reaches - 44cC (inner tank temp), or —47°C (outer or trim tank temp). However, regardless of the fuel type, the crew may consider delaying application of the procedure, until reaching the minimum fuel temperature specific to their fuel type (Refer to 3.01.28, page 1).
• On ground, before takeoff:
• IF JET A:
DELAY T.O.
Do not takeoff until the temperature is within limits.
• In flight
• If inner tank temp is less than —37°C (auto recall at —44°C)
Crew awareness.
• If outer tank temp is less than —40°C (auto recall at —47°C)
• IF JET A (not displayed at —47°C)
— OUTER TK TFR . . . . . . . . . . . . . . . . . . . . . . ON
• If trim tank temp is less than —40°C (auto recall at —47°C)
• IF JET A (not displayed at —47°C)
— TRIM TANK .................................................ON
If the trim tank pump fails, this part of the procedure is replaced by:
WHEN SPD> 270 KT AND NOT IN CLIMB:
—T TANK MODE FWD
— Fuel consumption increases by approximately 7%.
• IF NECESSARY:
— TAT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . INCREASE
Consider descent to a lower altitude and/or increasing Mach to increase TAT
The temperatures shown are dependent on engine type but only vary by 1 or 2 degrees. There is also a fuel temperature prediction program offered by Airbus that will predict fuel temperature issues on a given flight route, aircraft type and current met data.
Personally given the flight phase this occured, I wouldnt have thought it would be fuel waxing issue but as with most I'm awaiting the accident report.
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The initial AAIB report said 'after an uneventful flight...': could one imply from this that there was no EICAS warning about low fuel temp, hence no action was taken by the crew to increase fuel temp?
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Anotherflapoperator: With respect, you, and several others, have missed the point. If the fuel is so cold it wont flow, then... IT WONT FLOW. It doesn't matter how many heat exchangers there are, and how many relief valves bypasses or whatever are actuated. If it's turned to treacle it wont flow.
The other thing you have to realise is that hydrocarbon of any sort is a heterogeneous mixture. It sometimes does things that you don't expect. I once had a bloke turning up at my lab with a tanker full of bitumen that had set like rock. He'd loaded two lots of on-spec bitumen at different terminals. Separately, they were fine. Together, they were incompatible and set. I have had the same thing with heavy fuel oil incompatibility and wax falling out of diesel. Its rare but it happens. Maybe there was an incompatibility issue. Maybe there was a previously unknown additive package incompatibility between the fuel remaining after landing at Beijing and the uplift. Maybe the drip/retention sample used for analysis wasnt representative of the entire batch. Maybe someone screwed up and didnt drain the coalescer and it wasnt picked up at the hydrant servicer or bowser before loading. Anything is possible at this point.
Also, don't automatically assume skulduggery or incompetence. That uplift of fuel in Beijing may have been on spec. You may just have got a particularly waxy batch of fuel - or fuel with an associated dissolved water content (different from free water, which you can see) that worked fine in the lab test but under extreme and unusually cold conditions did not. The lab tests dont replicate what the engine sees: they simply look at a couple of dozen the physical characteristics. If it turns out that the test is not representative in extraordinary conditions, then that will probably mean a shake up in the fuel testing regime. For us oil heads, its an interesting in-vivo experiment. I just thank the Lord that no animals were harmed in this particular experiment.
Pinkman
The other thing you have to realise is that hydrocarbon of any sort is a heterogeneous mixture. It sometimes does things that you don't expect. I once had a bloke turning up at my lab with a tanker full of bitumen that had set like rock. He'd loaded two lots of on-spec bitumen at different terminals. Separately, they were fine. Together, they were incompatible and set. I have had the same thing with heavy fuel oil incompatibility and wax falling out of diesel. Its rare but it happens. Maybe there was an incompatibility issue. Maybe there was a previously unknown additive package incompatibility between the fuel remaining after landing at Beijing and the uplift. Maybe the drip/retention sample used for analysis wasnt representative of the entire batch. Maybe someone screwed up and didnt drain the coalescer and it wasnt picked up at the hydrant servicer or bowser before loading. Anything is possible at this point.
Also, don't automatically assume skulduggery or incompetence. That uplift of fuel in Beijing may have been on spec. You may just have got a particularly waxy batch of fuel - or fuel with an associated dissolved water content (different from free water, which you can see) that worked fine in the lab test but under extreme and unusually cold conditions did not. The lab tests dont replicate what the engine sees: they simply look at a couple of dozen the physical characteristics. If it turns out that the test is not representative in extraordinary conditions, then that will probably mean a shake up in the fuel testing regime. For us oil heads, its an interesting in-vivo experiment. I just thank the Lord that no animals were harmed in this particular experiment.
Pinkman
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cwatters
Please read 117 on page 6'
I was out of Singapore that night at 10600 mtrs across Russia. EICAS complained at -37 C fuel temp. Crossing into Germany we decended to FL340 with a TAT of -37 C. Fuel temp continued to drop. At - 40 C I decended to FL300 and temp carried on down to -41 despite a TAT of - 34. Then decided it was time to stop messing about and I decended to FL250 for the last hour in the cruise to LHR. Fuel began to warm up slowly at FL250.
All other flights in our vicinity from the Far East were decending that morniong at 0400Z for the same reason.
The 777 would have been on a more northely Flight Plan out of Shanghai and would have been in the cold air mass longer than us.
Undoubtably he would have had to decend with low fuel temps as well but if the temp guage/system was malfunctioning he may not have had a "low Fuel temp" EICAS msg.
All speculation of course but the cold air mass that morning was giving everyone problems
Please read 117 on page 6'
I was out of Singapore that night at 10600 mtrs across Russia. EICAS complained at -37 C fuel temp. Crossing into Germany we decended to FL340 with a TAT of -37 C. Fuel temp continued to drop. At - 40 C I decended to FL300 and temp carried on down to -41 despite a TAT of - 34. Then decided it was time to stop messing about and I decended to FL250 for the last hour in the cruise to LHR. Fuel began to warm up slowly at FL250.
All other flights in our vicinity from the Far East were decending that morniong at 0400Z for the same reason.
The 777 would have been on a more northely Flight Plan out of Shanghai and would have been in the cold air mass longer than us.
Undoubtably he would have had to decend with low fuel temps as well but if the temp guage/system was malfunctioning he may not have had a "low Fuel temp" EICAS msg.
All speculation of course but the cold air mass that morning was giving everyone problems
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What happened on subsequent 777 Beijing-LHR flights?
Have any malfunctions occurred on any subsequent flights BA flights, using the same route and altitudes - particularly where the meteorological conditions were similar?
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Re Pinkman 'no flow' hypothesis
As a humble driver, airframe, I am not qualified to judge the hydrocarbon physics involved here, but it seems to me these speculations don't go all the way in answering the question 'why only BA 038?' and 'why then?'. The fuel temp figures quoted by Chambudzi are well within mormal operating ranges for jet A-1 (but not jet A), and wouldn't by themselves have required a descent. They were also 7 hours earlier, so slightly lower temperature? But in any case, BA 038 would have spent a long time in the descent to Heathrow, during which the fuel would have warmed somehwat. This descent included apparently a hold at Lambourne, which would have required about the same EPR as final approach, and it appears to have done that with no problem (the flight was previously 'uneventful' according to the AAIB). By the time it got to finals the fuel would have been warmer still. Although it has been somewhat discredited since, Unctuous' theory about contamination in the fuel control system rather than the fuel flow per se seems to be closer to an explanation; my (1970) copy of 'the Jet Engine' shows a labyrinth of fuel tappings in the hydromechanical fuel control systems of the era, are they all now gone in this digital age? These tappings would presumably be more sensitive to contamination as fuel isn't actually flowing at speed through them. Just a thought.
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The engines may have spooled down low enough to cause the generators to trip off line. The engine auto relight feature would have kicked in I presume and everything back to normal except engines unable to spool up due to whatever!
It was really cold that day, temps were minus 71 degrees C and very un stable, airspeed was all over the place. Still for both engines to wax up within 8 seconds of each other is highly unlikely, also early descent into LHR and maybe holding (did they hold?) would have brought the temps back to about minus 12 ish for landing.
ps Does anyone know whether they tried EEC ALTN or even would it have made any difference IF it had been a FADEC fault? I know that on each start attempt the EEC's (on a 737) use the other channel. Or which thread and page this was discussed?
It was really cold that day, temps were minus 71 degrees C and very un stable, airspeed was all over the place. Still for both engines to wax up within 8 seconds of each other is highly unlikely, also early descent into LHR and maybe holding (did they hold?) would have brought the temps back to about minus 12 ish for landing.
ps Does anyone know whether they tried EEC ALTN or even would it have made any difference IF it had been a FADEC fault? I know that on each start attempt the EEC's (on a 737) use the other channel. Or which thread and page this was discussed?
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Freeze 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 hydrocarbon crystals form".
It's been a while, but the majority of JetA1/ Avtur batches I tested had a freeze point in the -57 to -60 degrees C range (Australia). Can't recall seeing one in the minus 40's..
Octane
It's been a while, but the majority of JetA1/ Avtur batches I tested had a freeze point in the -57 to -60 degrees C range (Australia). Can't recall seeing one in the minus 40's..
Octane
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Fuel control 777
What fuel supply point have both engines in common? What other control system have both engines in common? i.e. synchronization of EPR etc.
Surely, since both engines responded to throttles and then, after 3 seconds, reduced power, there must be a common cause.
Please note I am not knowledgable about the 777 systems but would like to see the above explained.
Surely, since both engines responded to throttles and then, after 3 seconds, reduced power, there must be a common cause.
Please note I am not knowledgable about the 777 systems but would like to see the above explained.
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Octane, thats absolutely my experience for JET A-1 freeze points also. As you know, the fuel in the tank never fully equilibrates with OAT for the reasons given elsewhere in this thread. So the theory is that if the aircraft spent a considerable amount of time at -70 C or below the viscosity of the fuel increased to a point where fuel flow was compromised even if it was at a higher temperature when that actually happened, because of the lag between ice/wax crystals forming and them melting. I have no idea where that happened in the fuel supply chain.
I dont know if there was a 'Lo fuel temp' EICAS message and if there was, whether it was acted upon. I do know that after the wing tank was punctured on landing the fuel would rapidly equilibrate and you wouldn't notice any change in physical properties in the fuel by the time you got to the scene. I do think that the eight seconds is incredibly significant because it points to an uncommanded common mode fault that was not software related. I think the fact that the engines responded then spooled down is not inconsistent with the above.
Thats all I know or think. I'm going back into lurk mode, as I've got nothing else to add really. Guess we should all wait for the next bulletin. I do hope that the retention samples were properly taken and that there is a proper chain of custody in their analysis, because we really need to know the answer, or to exclude fuel as the cause.
Pinkman
I dont know if there was a 'Lo fuel temp' EICAS message and if there was, whether it was acted upon. I do know that after the wing tank was punctured on landing the fuel would rapidly equilibrate and you wouldn't notice any change in physical properties in the fuel by the time you got to the scene. I do think that the eight seconds is incredibly significant because it points to an uncommanded common mode fault that was not software related. I think the fact that the engines responded then spooled down is not inconsistent with the above.
Thats all I know or think. I'm going back into lurk mode, as I've got nothing else to add really. Guess we should all wait for the next bulletin. I do hope that the retention samples were properly taken and that there is a proper chain of custody in their analysis, because we really need to know the answer, or to exclude fuel as the cause.
Pinkman
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There is one thing many of you seem to be forgetting.........
The fuel was never exposed to -70 outside air temperature (SAT or Static Air Temp). The wings and fuel temperatures would have been much warmer due to the heating effect of Ram Air (TAT or Total Air Temp)
The coldest the fuel should have been during the flight is -37C.
The fuel was never exposed to -70 outside air temperature (SAT or Static Air Temp). The wings and fuel temperatures would have been much warmer due to the heating effect of Ram Air (TAT or Total Air Temp)
The coldest the fuel should have been during the flight is -37C.
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Re TAT and minimum fuel temp
Slightly off thread, but why do all the text books say that the fuel temp will not decrease below TAT (transient effects aside)? TAT is reached only at the stagnation point, the rest of the wing surface (with which the fuel is in contact, after all) will be at a lower temperature, on average about SAT, but the upper surface will be lower still ('cos its lifting, hopefully). Chambudzi's post earlier suggested that on the same day his fuel went on cooling well below the TAT of -37, so perhaps we shouldn't regard this as more than folklore. No one ever explained it properly to me while I was aviating. Doesn't alter the fact that we have all seen temperatures as low as -44 in flight, but no engines stopped until Jan 17, and then only a long time after the minimum temp would have been reached.
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Chambudzi could be on track. 
http://www.aviationweek.com/aw/gener...0&channel=comm
We will see.
Regards
http://www.aviationweek.com/aw/gener...0&channel=comm
We will see.
Regards
Gentlemen... has your discussion of cold-fuel flow-characteristics lost the plot?
Unctuous, you led-off with a thought-provoking and (for many forumites) plausible hypothesis (January26/16:34). This has provoked a long discussion, which I have been following with increasing bewilderment.
Your argument seems to hinge on one premise: that the Trent-engine equivalent of the GE90's Ps3 and P3B sensors (which you refer to as "FADEC's reference port lines") could have been blocked by the icy component in cold, waxy fuel (see your post, paragraphs f, g and h).
But these types of sensors and their lines to the FADEC/EEC do not contain or transmit any fuel. They are situated in the engine itself, to sense the air pressure at whatever stage of the engine that the FADEC needs to know about (in this case, one of the compressor stages). They are not connected in any way to the engine fuel system.
The quoted FAA AD (Airworthiness Directive) relating to the GE90 engine seems to have been addressing a problem in which water had entered the probes during flight or on the ground, and then frozen before it had a chance to drain out through the drain-holes provided.
I quote from the original (superseded) AD:
"The investigation revealed that water can accumulate in the Ps3 and P3B pressure sensing system, which can freeze in the full authority digital engine control (FADEC) sensing ports or pressure line. Frozen water can result in a restriction or a blocked signal to the FADEC. This blocked signal can cause a corruption of the FADEC signal and result in abnormal engine start characteristics on the ground or lack of engine response to commanded thrust levels in flight."
The "water" they are referring to comes from rain or spray, not water in fuel.
The FADEC/EEC needs to know these air pressures, in order to assess an engine's current thrust setting. It will then adjust the fuel flow accordingly (among other things).
Hope that helps...
Your argument seems to hinge on one premise: that the Trent-engine equivalent of the GE90's Ps3 and P3B sensors (which you refer to as "FADEC's reference port lines") could have been blocked by the icy component in cold, waxy fuel (see your post, paragraphs f, g and h).
But these types of sensors and their lines to the FADEC/EEC do not contain or transmit any fuel. They are situated in the engine itself, to sense the air pressure at whatever stage of the engine that the FADEC needs to know about (in this case, one of the compressor stages). They are not connected in any way to the engine fuel system.
The quoted FAA AD (Airworthiness Directive) relating to the GE90 engine seems to have been addressing a problem in which water had entered the probes during flight or on the ground, and then frozen before it had a chance to drain out through the drain-holes provided.
I quote from the original (superseded) AD:
"The investigation revealed that water can accumulate in the Ps3 and P3B pressure sensing system, which can freeze in the full authority digital engine control (FADEC) sensing ports or pressure line. Frozen water can result in a restriction or a blocked signal to the FADEC. This blocked signal can cause a corruption of the FADEC signal and result in abnormal engine start characteristics on the ground or lack of engine response to commanded thrust levels in flight."
The "water" they are referring to comes from rain or spray, not water in fuel.
The FADEC/EEC needs to know these air pressures, in order to assess an engine's current thrust setting. It will then adjust the fuel flow accordingly (among other things).
Hope that helps...
Last edited by Chris Scott; 27th Jan 2008 at 15:11.
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Ice
Can't see how water contamination could be an issue if temps down to -35 or below. As we know, water freezes at 0 celcius, problem would have manifested itself earlier inflight if an issue... (water/ice denser than fuel, 1.0 versus 0.7)
Octane
Octane
A380focal got in first
Whoops! The first 3 paragraphs of your post #100 put the argment better than I have just done.
Sorry I missed it - among all the chaff... At least it gives us both another chance to restore simple reality - on one issue at least.
Chris
Sorry I missed it - among all the chaff... At least it gives us both another chance to restore simple reality - on one issue at least.
Chris