BA038 (B777) Thread
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Forgive me for not checking all sixty odd pages of this thread for the answers to the following.
Is there a temperature sensor anywhere near the fuel pumps - particularly the H.P. ?
Is that data recorded anywhere ?
What was the temperature of the fuel either side of the H.P. pumps at the time of engine failure ?
Is there a temperature sensor anywhere near the fuel pumps - particularly the H.P. ?
Is that data recorded anywhere ?
What was the temperature of the fuel either side of the H.P. pumps at the time of engine failure ?
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Goose
There is one Fuel Probe (Temp. Sensor) Data stored in FDR. It is located between Ribs nine and ten in the Port Wing, about one meter aft of the Boost Pump Pickup as I recall.
Airfoil
(Lowest Recorded Temp. Fuel was -38C.) And the Port wing was on the Sun Side of the A/C for that flight.
Airfoil
(Lowest Recorded Temp. Fuel was -38C.) And the Port wing was on the Sun Side of the A/C for that flight.
It is interesting that the FAA are now looking at the suction feed.Here is my post from way back, which may be an explanation:
There is actually one instance in which Boeing suggest that a fuel supply problem can cause engine thrust deterioration or flame out. This is when an engine has to revert to suction feed at altitude, following dual wing tank pump failure. (No mention is made of the low altitude situation.) The background to this advisory is that dissolved air in the fuel is released at altitude and can accumulate in the suction feed pipe. The implication being that low atmospheric pressure in the tank, plus air in the suction line will disrupt or cut off the fuel flow under suction conditions.
Note from the fuel synoptic posted by Jet11 that the suction pipe is connected directly to the engine fuel supply manifold, isolated only by a pressure bypass valve. Also that the tank pump nominal output pressure is 14psi, but can be much lower. For argument's sake, I will assume that the suction bypass valve opens when there is a pressure differential around 5 psi and it closed under normal conditions.
In Bejjing, BA038 takes on fuel with an unusually high dissolved air content. This is due to a combination of production/storage/transportation/pumping and weather variables. The a/c flies high, long and cold. The air is released from the fuel and the suction pipe is completely filled with (relatively) dense air. This air remains in the pipe during the descent and once below 6000ft is inceasingly pressurised by denser ambient air and rising temperatures. At 1000ft atmospheric pressure reaches 14psi, equalling the fuel manifold pressure. Fuel hydrostatic static pressure and adiabetic heating add another 6psi, causing the suction bypass valve to open against tank pump pressure.This releases pressurised air into the fuel supply manifold and disrupts the fuel supply. This happens in both tanks, but not simultaneously. The opening of the valve could be assisted by a momentary drop in fuel manifold pressure during the initial power demand.
Just another theory. My assumptions about the bypass valve are probably wrong. Also, why is this not a regular occurence? Maybe the fuel and meteorological conditions were unique to BA38. Maybe we have always been operating close to this scenario.........
There is actually one instance in which Boeing suggest that a fuel supply problem can cause engine thrust deterioration or flame out. This is when an engine has to revert to suction feed at altitude, following dual wing tank pump failure. (No mention is made of the low altitude situation.) The background to this advisory is that dissolved air in the fuel is released at altitude and can accumulate in the suction feed pipe. The implication being that low atmospheric pressure in the tank, plus air in the suction line will disrupt or cut off the fuel flow under suction conditions.
Note from the fuel synoptic posted by Jet11 that the suction pipe is connected directly to the engine fuel supply manifold, isolated only by a pressure bypass valve. Also that the tank pump nominal output pressure is 14psi, but can be much lower. For argument's sake, I will assume that the suction bypass valve opens when there is a pressure differential around 5 psi and it closed under normal conditions.
In Bejjing, BA038 takes on fuel with an unusually high dissolved air content. This is due to a combination of production/storage/transportation/pumping and weather variables. The a/c flies high, long and cold. The air is released from the fuel and the suction pipe is completely filled with (relatively) dense air. This air remains in the pipe during the descent and once below 6000ft is inceasingly pressurised by denser ambient air and rising temperatures. At 1000ft atmospheric pressure reaches 14psi, equalling the fuel manifold pressure. Fuel hydrostatic static pressure and adiabetic heating add another 6psi, causing the suction bypass valve to open against tank pump pressure.This releases pressurised air into the fuel supply manifold and disrupts the fuel supply. This happens in both tanks, but not simultaneously. The opening of the valve could be assisted by a momentary drop in fuel manifold pressure during the initial power demand.
Just another theory. My assumptions about the bypass valve are probably wrong. Also, why is this not a regular occurence? Maybe the fuel and meteorological conditions were unique to BA38. Maybe we have always been operating close to this scenario.........
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Don't put to much on this AD, as this has been known about for over two years or more.
You will find that this task has been in operation for a few years and BA may have been doing it on its B777 fleet.
I was at a Boeing engineering committee a few years back on the B757 series and we were told that a new task was being introduced to carry out a fuel suction test, which we voted to accept.
I remember way back this being done on the old B737-200s and we were told at our meeting it had come about from findings on the B777 fleet. Due to the fuel system on the B757 being similar to that of the B777, it needed to be brought in. We discussed the interval that was proposed and made amendments to the interval and was as l said accepted.
We were told if we accepted the task, it would mean that it should not have to be made an AD. This task was introduced into our "C" checks two winters back.
So if the same thing has happened to the B777, l would guess it has been carried out for a couple of years.
The main reason for the task, is when you get low fuel quantity you may suck air in, if the fuel pipe seals are leaking. You need a very low fuel figure in each tank to carry out the check using engine runs or you have go into the tanks and use test equipment instead to check the piping.
You will find that this task has been in operation for a few years and BA may have been doing it on its B777 fleet.
I was at a Boeing engineering committee a few years back on the B757 series and we were told that a new task was being introduced to carry out a fuel suction test, which we voted to accept.
I remember way back this being done on the old B737-200s and we were told at our meeting it had come about from findings on the B777 fleet. Due to the fuel system on the B757 being similar to that of the B777, it needed to be brought in. We discussed the interval that was proposed and made amendments to the interval and was as l said accepted.
We were told if we accepted the task, it would mean that it should not have to be made an AD. This task was introduced into our "C" checks two winters back.
So if the same thing has happened to the B777, l would guess it has been carried out for a couple of years.
The main reason for the task, is when you get low fuel quantity you may suck air in, if the fuel pipe seals are leaking. You need a very low fuel figure in each tank to carry out the check using engine runs or you have go into the tanks and use test equipment instead to check the piping.
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But are you assuming the T7 has a separate supply, isolated from the pumps/line that "takes over" when Pumps inop? The mass of Fuel in the pipeline has great inertia at low/no velocity and with HP functional at 14psi (or slightly greater) could vaporise regardless of Temp. One atmosphere is ~ 14psi, right? In a "tail low" approach, the suction problem could be exacerbated by the inertia of the Fuel and its lethargic velocity in the Line due to Green descent. Haven't we been there? (Besides, the pumps were working, AAIB)
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I am suprised no one has picked up on this.
http://www.ainonline.com/news/single-news-page/article/fuel-system-remains-focus-of-investigation-into-ba-777-crash/
Fuel system remains focus of investigation into BA 777 crash
By Ian Goold
June 1, 2008
Accidents
Safety officials probing the circumstances leading to the January 17 accident of a British Airways (BA) Boeing 777 at London Heathrow are continuing to focus on the fuel system. In particular, they want to know why the aircraft lost power when it was on final approach.
The 777, operating as flight BA038, was flying nonstop from Beijing to London Heathrow. The flight was uneventful and the engine operation was normal until the final approach. As the 777 approached to land, the R-R Trent 895 engines initially responded to an autothrottle command for increased thrust. At a height of about 720 feet, thrust on the right engine reduced to about 1.03 times the engine pressure ratio (EPR), followed about seven seconds later by a similar reduction (1.02 EPR) on the left engine.
The airplane touched down 1,000 feet short of Runway 27L’s paved surface before coming to rest in the undershoot area astride a taxiway junction near the threshold. In the heavy landing, the nosegear collapsed and the left main undercarriage was punched up through the upper surface of the wing, while the right undercarriage six-wheel bogie detached from the aircraft. One passenger was seriously injured and 12 other occupants received minor injuries. The airplane sustained heavy damage and was subsequently written off.
The UK Air Accidents Investigation Branch (AAIB) has determined that in the case of both engines, thrust reduction resulted from reduced fuel flow, which was reflected in all subsequent engine parameters. Although the fuel-metering valve responded to an engine-control system command to open fully, there was “no appreciable change” in fuel flow. Evidence indicated that both engines had “low fuel pressure at the inlet to the high-pressure pump.”
Following “sustained interest” in the accident, the first such event involving a 777, the AAIB last month published a special bulletin that said Boeing Commercial Airplanes division was conducting fuel-system testing in Seattle. Engine manufacturer Rolls-Royce had earlier completed “extensive full-scale engine testing” in a cell modified to replicate the actual response of the accident aircraft’s engine fuel and control system.
AAIB investigators say the primary challenge was for Boeing to create the environmental conditions the flight experienced while flying over Siberia at altitudes of up to 40,000 feet. The flight over the region took the 777 through particularly cold air, as low as -76 degrees Celsius (-104.8 degrees F). The minimum recorded fuel temperature was -34 degrees Celsius (-29.2 degrees F) and subsequent tests of onboard fuel showed a freezing temperature of -57 degrees Celsius (-70.6 degrees F).
Investigators are principally concerned with understanding the potential for
fuel-system restrictions to have formed. Additional work has aimed to improve understanding of fuel-flow dynamics between the tank and the engine.
Systems consultancy Qinetiq is reviewing recorded data from a large number of similar flights. Qinetiq analysts are concentrating on the identification of abnormal combinations of parameters, since no single reading from the accident flight has been identified as outside previous type operating experience.
http://www.ainonline.com/news/single-news-page/article/fuel-system-remains-focus-of-investigation-into-ba-777-crash/
Fuel system remains focus of investigation into BA 777 crash
By Ian Goold
June 1, 2008
Accidents
Safety officials probing the circumstances leading to the January 17 accident of a British Airways (BA) Boeing 777 at London Heathrow are continuing to focus on the fuel system. In particular, they want to know why the aircraft lost power when it was on final approach.
The 777, operating as flight BA038, was flying nonstop from Beijing to London Heathrow. The flight was uneventful and the engine operation was normal until the final approach. As the 777 approached to land, the R-R Trent 895 engines initially responded to an autothrottle command for increased thrust. At a height of about 720 feet, thrust on the right engine reduced to about 1.03 times the engine pressure ratio (EPR), followed about seven seconds later by a similar reduction (1.02 EPR) on the left engine.
The airplane touched down 1,000 feet short of Runway 27L’s paved surface before coming to rest in the undershoot area astride a taxiway junction near the threshold. In the heavy landing, the nosegear collapsed and the left main undercarriage was punched up through the upper surface of the wing, while the right undercarriage six-wheel bogie detached from the aircraft. One passenger was seriously injured and 12 other occupants received minor injuries. The airplane sustained heavy damage and was subsequently written off.
The UK Air Accidents Investigation Branch (AAIB) has determined that in the case of both engines, thrust reduction resulted from reduced fuel flow, which was reflected in all subsequent engine parameters. Although the fuel-metering valve responded to an engine-control system command to open fully, there was “no appreciable change” in fuel flow. Evidence indicated that both engines had “low fuel pressure at the inlet to the high-pressure pump.”
Following “sustained interest” in the accident, the first such event involving a 777, the AAIB last month published a special bulletin that said Boeing Commercial Airplanes division was conducting fuel-system testing in Seattle. Engine manufacturer Rolls-Royce had earlier completed “extensive full-scale engine testing” in a cell modified to replicate the actual response of the accident aircraft’s engine fuel and control system.
AAIB investigators say the primary challenge was for Boeing to create the environmental conditions the flight experienced while flying over Siberia at altitudes of up to 40,000 feet. The flight over the region took the 777 through particularly cold air, as low as -76 degrees Celsius (-104.8 degrees F). The minimum recorded fuel temperature was -34 degrees Celsius (-29.2 degrees F) and subsequent tests of onboard fuel showed a freezing temperature of -57 degrees Celsius (-70.6 degrees F).
Investigators are principally concerned with understanding the potential for
fuel-system restrictions to have formed. Additional work has aimed to improve understanding of fuel-flow dynamics between the tank and the engine.
Systems consultancy Qinetiq is reviewing recorded data from a large number of similar flights. Qinetiq analysts are concentrating on the identification of abnormal combinations of parameters, since no single reading from the accident flight has been identified as outside previous type operating experience.
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F111D - A summary of 68 pages... The evidence for lack of fuel flow appears to be limited to minor cavitation damage to the pumps (Minor in the sense that it did not stop them working). The issue is what caused the low fuel pressure/flow in the first place. It appears there was sufficient fuel on the plane.
Airfoilmode:
No, I am not suggesting that the suction system has its own fuel supply line. There is a short section of pipe that joins the main fuel supply manifold, via a check valve, just downstream of the LP tank pumps. I would not see fuel inertia as a problem there.
What I suggested was that air or gas that was trapped in the suction pick-up pipe might, under certain circumstances, become sufficiently pressurised to enable it to overcome the check valve differential and discharge like an aerosol into the main manifold. When this air/gas reached the engine HP pumps it would cause cavitation as the pumps ingested air and fuel supply to the engines would be reduced, similar to the situation where a diesel engine loses pressure at the injectors if air gets in the system. No doubt the LP pumps would have restored manifold pressure eventually, but in BA038's case there was insufficient time before the accident occurred.
Maybe the check valves have prevented this situation up to now and BA038 was the first unlucky one. Running a suction check from time to time would certainly remove any trapped gases in the system.
No, I am not suggesting that the suction system has its own fuel supply line. There is a short section of pipe that joins the main fuel supply manifold, via a check valve, just downstream of the LP tank pumps. I would not see fuel inertia as a problem there.
What I suggested was that air or gas that was trapped in the suction pick-up pipe might, under certain circumstances, become sufficiently pressurised to enable it to overcome the check valve differential and discharge like an aerosol into the main manifold. When this air/gas reached the engine HP pumps it would cause cavitation as the pumps ingested air and fuel supply to the engines would be reduced, similar to the situation where a diesel engine loses pressure at the injectors if air gets in the system. No doubt the LP pumps would have restored manifold pressure eventually, but in BA038's case there was insufficient time before the accident occurred.
Maybe the check valves have prevented this situation up to now and BA038 was the first unlucky one. Running a suction check from time to time would certainly remove any trapped gases in the system.
777fly-
Air bubbles in the fuel do not cause cavitation damage. The air cushions the collapse of the air bubble, so the bubble does not disappear when pressure is restored, and there is no damaging shock wave.
Air bubbles in the fuel do not cause cavitation damage. The air cushions the collapse of the air bubble, so the bubble does not disappear when pressure is restored, and there is no damaging shock wave.
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To save you rushing to download, there is nothing of note in it, and still no mention of a config change, and no rec. of any changes in operating procedures.
Too mean to buy a long personal title
Indeed - in fact, it looks to me like it's exactly the same document as was published on 12 May 2008, just formatted differently to be incorporated into the Bulletin.
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Rightbase is correct, air in the fuel stream will not cause cavitation damage, for the reasons he stated. This was caused by a fuel obstruction or restriction.
In fact, if you think about it, cavitation damage from suction would seem to confirm integrity of the fuel manifold.
In fact, if you think about it, cavitation damage from suction would seem to confirm integrity of the fuel manifold.
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When the freezing point of fuel is measured on the ground is the resulting figure corrected for the increased pressure found in the fuel system?
I think the freezing point of fuel (but not water) is raised by increasing pressure. In which case you might speculate on the possibility of having liquid fuel in the tank... which then freezes in the pipes/pumps when pressurised.
This effect probably isn't great enough though.... -34C to -57C is a bit of a stretch and the architecture of the 777 fuel system may also rule this out.
Edit: Initially when you compress something heat is given out which raises the temperature. At high flow rates the fuel might remain warmed. At low flow rates perhaps this heat has time to disipate leaving the higher freezing point to cause the problem. If that's correct it might explain why this didn't happen in cruise just on approach.
I think the freezing point of fuel (but not water) is raised by increasing pressure. In which case you might speculate on the possibility of having liquid fuel in the tank... which then freezes in the pipes/pumps when pressurised.
This effect probably isn't great enough though.... -34C to -57C is a bit of a stretch and the architecture of the 777 fuel system may also rule this out.
Edit: Initially when you compress something heat is given out which raises the temperature. At high flow rates the fuel might remain warmed. At low flow rates perhaps this heat has time to disipate leaving the higher freezing point to cause the problem. If that's correct it might explain why this didn't happen in cruise just on approach.
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Or it might just be the difference between finding the fault on a complete and serviceable airplane and not finding or unable to duplicate the fault on an incomplete and twisted one?
For instance, if something was in error in the last few minutes of the flight, a sequence of system selections unique to the approach phase only, which generated a rogue electrical spike that did not make it to the recorders somehow? Maybe the temperature in the fuel tanks had nothing to do with the cause at all, perhaps humidity, pressure and temperature inside the hull and miles of wiring and electronic units did?
Green-dot
For instance, if something was in error in the last few minutes of the flight, a sequence of system selections unique to the approach phase only, which generated a rogue electrical spike that did not make it to the recorders somehow? Maybe the temperature in the fuel tanks had nothing to do with the cause at all, perhaps humidity, pressure and temperature inside the hull and miles of wiring and electronic units did?
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Don't put to much on this AD, as this has been known about for over two years or more.
http://www.pprune.org/forums/showpost.php?p=4000971&postcount=1101
FAA has specifically said the suction AD is nothing to do with BA038.
Can you provide a link to this statement by the FAA that the AD has nothing to do with BA038?
Thanks.
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As has been addressed before, the Trent/777 does just fine in Suction only regime. Also, prior post (recent) explains that a non uniform Fuel supply (eg entrained air) would prevent cavitation, not cause it. Air/Water/Additives in the Fuel have been addressed pretty much ad nauseum. I think the chances the AD is related to BA038 are quite slim, except as it may apply to the Fleet in general, though not nil. (Consider 7,500 TBI per AD)
My sense of the cavitation problem would require cold Fuel in a tight system, devoid of easily vaporised contaminants, subjected to a sudden throttle slam shock with HP's straining at a volume of Line Fuel that has substantial inertia, creating cavitation, which in turn would inhibit the free flow of Fuel. A perceived restriction/block is in there as well.
Airfoil
My sense of the cavitation problem would require cold Fuel in a tight system, devoid of easily vaporised contaminants, subjected to a sudden throttle slam shock with HP's straining at a volume of Line Fuel that has substantial inertia, creating cavitation, which in turn would inhibit the free flow of Fuel. A perceived restriction/block is in there as well.
Airfoil
Last edited by airfoilmod; 14th Jun 2008 at 15:30.
cwatters, hi again,
A minor point, fuel cannot be compressed just pressurised although any air present would be compressed.
A minor point, fuel cannot be compressed just pressurised although any air present would be compressed.
Last edited by Oldlae; 14th Jun 2008 at 17:28. Reason: further thoughts
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"PickyPerkins", your link has nothing l believe, to do with this AD.
As l pointed out this MRB task and now being made into an AD, is all about air being sucked into the fuel tank piping from within the tank, from worn seals where the pipes join each other.
This happens with very low fuel state and would not happen just after take-off.
What happened to the UA aircraft, is l believe not related to this extra task introduced from the MRB and now mandated.
As l pointed out this MRB task and now being made into an AD, is all about air being sucked into the fuel tank piping from within the tank, from worn seals where the pipes join each other.
This happens with very low fuel state and would not happen just after take-off.
What happened to the UA aircraft, is l believe not related to this extra task introduced from the MRB and now mandated.