AAIB BA38 B777 Initial Report Update 23 January 2008
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QUOTE:
I also understand they had had an continuous(ish) descent, and no holding LAM or elsewhere.
Actually they did 1 circuit of LAM, and the descent was indeed continuous.
I also understand they had had an continuous(ish) descent, and no holding LAM or elsewhere.
Actually they did 1 circuit of LAM, and the descent was indeed continuous.
Flightman, you seem to have inside information (?). If the descent was continuous, even in the hold at Lambourne, was it steep enough to avoid significant spool-up when they were not slowing down?
Quote (#66):
What we do not yet know is: what happened earlier during the descent and approach? Could the demand for more thrust at T+0 have been the first since top-of-descent? On a daytime arrival into LHR, that would be (sadly) a very rare event. So, assuming thrust above idle was needed earlier (e.g., on initial approach, or to stabilise at 160 kts till 4 miles for ATC spacing) how did the engines respond to the autothrottle demands?
If the engines had gradually been contaminated with dirty or waxed fuel, would this not have been revealed earlier? Why did the two engines suffer no apparent problems until 600 ft, and then - despite feeding from separate tanks - only 8 seconds apart?
Unquote.
Also, would the increased TAT and SAT in at least 20 minutes of the descent not have de-waxed the fuel, as has previously been suggested?
Quote (#66):
What we do not yet know is: what happened earlier during the descent and approach? Could the demand for more thrust at T+0 have been the first since top-of-descent? On a daytime arrival into LHR, that would be (sadly) a very rare event. So, assuming thrust above idle was needed earlier (e.g., on initial approach, or to stabilise at 160 kts till 4 miles for ATC spacing) how did the engines respond to the autothrottle demands?
If the engines had gradually been contaminated with dirty or waxed fuel, would this not have been revealed earlier? Why did the two engines suffer no apparent problems until 600 ft, and then - despite feeding from separate tanks - only 8 seconds apart?
Unquote.
Also, would the increased TAT and SAT in at least 20 minutes of the descent not have de-waxed the fuel, as has previously been suggested?
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Somewhere I think I remember reading that there is a difference in the physical fuel flow to the left and right engines - something to do with the oil/fuel heat exchanger?
Is this correct or is my memeory up the spout?
Is this correct or is my memeory up the spout?
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Tree:
Jet A1 will freeze at -47 C. Considering the amount of fuel 777 was carrying SAT -60 is not cold enough to freeze it on the way from PEK to LHR. In the NW parts of Russia SAT has been around -70 (~FL390) lately, but even that is not cold enough. I have been flying (A340) many times in temperatures like -76 SAT and even in that temperature it takes hours before fuel temp in outer tanks (wing tip) drop below -40. In inner tanks temperatures are then still well over -40 deg.
That is not true of the 6 different aircraft types I have operated
(Lockheed, Boeing, Airbus) In my experience any prolonged exposure to a SAT of -60 or more has caused fuel temps well below -37C and required a modification to the flight envelope. The small Airbus models are especially affected.
(Lockheed, Boeing, Airbus) In my experience any prolonged exposure to a SAT of -60 or more has caused fuel temps well below -37C and required a modification to the flight envelope. The small Airbus models are especially affected.
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Somewhere I think I remember reading that there is a difference in the physical fuel flow to the left and right engines - something to do with the oil/fuel heat exchanger?
Is this correct or is my memeory up the spout?
No. The engine fuel/oil heat exchanger is on the engine. It is the same on all Trents.
What is confusing you is that the hydraulic oil pump case drain filter heat exchangers are in the fuel tanks. Two in one wing tank and one in the other. These cool the skydrol that runs through them, and in so doing impart heat to the fuel in the tank. This heat is nearly not measurable.
Is this correct or is my memeory up the spout?
No. The engine fuel/oil heat exchanger is on the engine. It is the same on all Trents.
What is confusing you is that the hydraulic oil pump case drain filter heat exchangers are in the fuel tanks. Two in one wing tank and one in the other. These cool the skydrol that runs through them, and in so doing impart heat to the fuel in the tank. This heat is nearly not measurable.
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This "incident" is going to cost the industry Billions.
This "incident" is going to cost the industry Billions. Yes it is!
An incident like this due to low fuel temperatures will re-write the book on long cold flights, fly lower and faster.
If the fact that BA38 managed to fly over four thousand miles and augered in just a quarter of a mile short of the runway with no prior indication anything was wrong is an indication that all the sensing of fuel temperatures and metering is a load of bollocks as currently applied.
Looking at this incident another way, all the sophisticated systems on the 777 made the aircraft perform flawlessly for over eleven hours, then, due to some "fuel" temperature unforseen circumstance an engine quit.
Hey I can understand that, these things happen.
What I am having some difficulty believing that the second engine, with a different fuel supply and totally seperate sensing and control system quit FIVE SECONDS after the first one did!!!!
Waiting for the final report......
An incident like this due to low fuel temperatures will re-write the book on long cold flights, fly lower and faster.
If the fact that BA38 managed to fly over four thousand miles and augered in just a quarter of a mile short of the runway with no prior indication anything was wrong is an indication that all the sensing of fuel temperatures and metering is a load of bollocks as currently applied.
Looking at this incident another way, all the sophisticated systems on the 777 made the aircraft perform flawlessly for over eleven hours, then, due to some "fuel" temperature unforseen circumstance an engine quit.
Hey I can understand that, these things happen.
What I am having some difficulty believing that the second engine, with a different fuel supply and totally seperate sensing and control system quit FIVE SECONDS after the first one did!!!!
Waiting for the final report......
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Every Anorak and those of the misguided religions that have posted complete twaddle, disguised as factual opinion, should be set in the stocks and pounded with cabbages, tomatoes and absolutely anything smelly that comes to hand, after the final report is in 
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Tree:
The U.S. Antarctic program used Diesel Fuel Arctic (DFA) for everything
(jets, turboprops and helos, diesels of every size, and furnaces) up to some time in the 1990s, when they went to the US military standard, JP-8.
I know of no aircraft mishaps there from fuel temperature problems with either fuel. C-130 ops are conducted down to -65F at the surface, limited by landing gear fragility. At those temps, engines must be left running - cold starts have a good possibility of prop seal damage, and there are no hangars, heated or otherwise, at Spole.
(jets, turboprops and helos, diesels of every size, and furnaces) up to some time in the 1990s, when they went to the US military standard, JP-8.
I know of no aircraft mishaps there from fuel temperature problems with either fuel. C-130 ops are conducted down to -65F at the surface, limited by landing gear fragility. At those temps, engines must be left running - cold starts have a good possibility of prop seal damage, and there are no hangars, heated or otherwise, at Spole.
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A380focal
On this basis if the throttles didn't move in line with the FADEC demand the problem could have been quietly brewing for hours in the cruise without any indication to the flight deck crew.
During the latter part of the flight the fuel flow in the cruise would have been about the same as on final approach.
One other point we don't know how much cargo was on the aircraft but 130ish passengers would equate to about 12 tonnes payload. A 777 at a low weight could well be at or above FL400. Does anyone know the flight profile of the aircraft?
The same would be true for any blockage to the fuel upstream of engine - it opens the valve more and more, but no more thrust is coming. The FADEC is confused in a way - but this does not cause a lack of thrust - the lack of thrust would result from the engine not getting fuel due to a blockage.
During the latter part of the flight the fuel flow in the cruise would have been about the same as on final approach.
One other point we don't know how much cargo was on the aircraft but 130ish passengers would equate to about 12 tonnes payload. A 777 at a low weight could well be at or above FL400. Does anyone know the flight profile of the aircraft?
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Seldomfixit & soggy_cabbage
Every Anorak and those of the misguided religions that have posted complete twaddle, disguised as factual opinion, should be set in the stocks and pounded with cabbages, tomatoes and absolutely anything smelly that comes to hand, after the final report is in
What I am having some difficulty believing that the second engine, with a different fuel supply and totally seperate sensing and control system quit FIVE SECONDS after the first one did!!!
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The FADEC does not measure fuel pressure - there are no little pipes with fuel in them connected to the FADEC that can get confused. The FADEC does measure fuel flow, but it does not need this for primary control. The FADEC control system is closed loop - you demand a thrust - the valve moves to a position it thinks will give you the desired thrust. If the FADEC determines that thrust has not been achieved then it would open the valve some more until the thrust is achieved.
The only way therefore that wax / ice in the fuel arriving at the engine (discounting the fact that the two pumps and a fuel / oil heat exhanger are the first things it meets!) would confuse the FADEC is that it would keep opening the valve more and more, but would not be seeing any increase in thrust! The same would be true for any blockage to the fuel upstream of engine - it opens the valve more and more, but no more thrust is coming. The FADEC is confused in a way - but this does not cause a lack of thrust - the lack of thrust would result from the engine not getting fuel due to a blockage.
This is a fact - by the nature that the engine is controlled the FADEC cannot be corrupted by wax resulting in loss of thrust. The engine will produce a loss of thrust if it doesn't get enough fuel....
The only way therefore that wax / ice in the fuel arriving at the engine (discounting the fact that the two pumps and a fuel / oil heat exhanger are the first things it meets!) would confuse the FADEC is that it would keep opening the valve more and more, but would not be seeing any increase in thrust! The same would be true for any blockage to the fuel upstream of engine - it opens the valve more and more, but no more thrust is coming. The FADEC is confused in a way - but this does not cause a lack of thrust - the lack of thrust would result from the engine not getting fuel due to a blockage.
This is a fact - by the nature that the engine is controlled the FADEC cannot be corrupted by wax resulting in loss of thrust. The engine will produce a loss of thrust if it doesn't get enough fuel....
Indeed. The FADEC doesn't even have to be on the engine. Providing it gets the neccesary digital inputs it can be located anywhere on the aircraft
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Answers to some of the moderately technical questions that crop up about the 777 can be found here:
http://www.boeing.com/commercial/airports/777.htm
http://www.boeing.com/commercial/airports/777.htm
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To try to clarify:
The term "freezing point" for Jet-A1 is maybe somewhat misleading. It's basically the temperature below where the normally "transparent" fuel shows its first traces of "milkiness". Diesel guys refer to this as the Cloud Point. The flow is not impaired at this temperature.
The dangeruos temperature is where the fuel has thickened so much it's practically not a liquid anymore. Diesel guys refer to this as the CFPP or Cold Filter Plugging Point. For Jet-A1, I've not seen a corresponding term, presumably because this temperature range below the "freezing point" is a no-go area that provides the required safety margin.
For diesel, the temperature margin between the CP and CFPP can be between -5 and -15 degrees C depending on fuel composition, fuel system design and probably other factors as well. In land vehicles one may utilize this margin, but it pays to be prepared for filter clogging. I saw a corresponding figure of -6 degrees C for Jet-A1, but there is obviously some variation in this case too.
The term "freezing point" for Jet-A1 is maybe somewhat misleading. It's basically the temperature below where the normally "transparent" fuel shows its first traces of "milkiness". Diesel guys refer to this as the Cloud Point. The flow is not impaired at this temperature.
The dangeruos temperature is where the fuel has thickened so much it's practically not a liquid anymore. Diesel guys refer to this as the CFPP or Cold Filter Plugging Point. For Jet-A1, I've not seen a corresponding term, presumably because this temperature range below the "freezing point" is a no-go area that provides the required safety margin.
For diesel, the temperature margin between the CP and CFPP can be between -5 and -15 degrees C depending on fuel composition, fuel system design and probably other factors as well. In land vehicles one may utilize this margin, but it pays to be prepared for filter clogging. I saw a corresponding figure of -6 degrees C for Jet-A1, but there is obviously some variation in this case too.
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Snowfalcon is 100% correct. The reference to diesel is interesting because diesel contamination is known to raise the freezing point of aviation fuels. The following is an interesting read (although its a promo):
http://www.sartec.co.uk/News/mod-pr.htm
http://www.sartec.co.uk/News/mod-pr.htm
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Re Diesel contamination
Pinkman. Just to get it straight in my mind. We seem to have a suggestion of a type of fuel contamination that can raise the freeze point. So this allows high power for take-off climb and cruise, but also allows significant waxing after a long cold soak at altitude (and the temps were apparently rather low that day). From TOD to Lambourne engines may well have been idle all the way, if there were any restriction it wasn't enough to snuff them out at low power. But in 35 years of operating to Heathrow I don't think I ever did an idle descent from cruise level to finals, especially not on a windy day like Jan 17. As everyone knows, ATC can't maintain flow in headwinds, the rules don't allow them to (constant distance spacing = increased time separation); even if they didn't hold at LAM (and we don't seem to know that for sure), or even if they descended continuously in the hold, I can't believe they didn't do the obligatory shuffle 270 deg off LAM level at FL 70. That would have required modest EPR, similar to final approach. But the engines responded then. Is it the suggestion that the higher fuel flow then dislodged a 'plug' of wax (?) from wherever it was sitting happily to somewhere closer to the engines, to then move fatally somewhere else when the final power demand was made (rather like a deep vein thrombosis moves from the legs to the heart or lungs, as I understand it)? I might even buy it.