AAIB BA38 B777 Initial Report Update 23 January 2008
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Would this imply something wrong, or out of spec, with the uplifted fuel?
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As you say, <<"the reduced thermal capacity of the remaining fuel means it does warm significantly by the start of approach">>. Those waxy globules wouldn't be likely to emulsify back into solution; they'd just break down, as described, into smaller units and migrate downstream that much more readily (particularly once the demands of a throttle up starts sucking them through). Engines under acceleration demands have always been vulnerable to poorly adjusted AFRCU's or (so it would appear) to FADECs and EEC computers in receipt of outside-of-normal-parameter data.
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Can someone explain a bit further the AD referred to in UNCTUOUS's post?
The AD goes on to say that the engines then continued to operate normally.
Since the incidents occurred at altitude, how could this be? Unless the ice melted at altitude, wouldn't the sensor continue to remain blocked, and the FADEC contiue to be fed corrupted data?
Is it assumed that the ice melted at altitude after the LOTC event, or was a considerable loss of altitude and descent into warmer air involved?
If the engines were re-started at altitude, does the FADEC ignore the blocked Ps3 signal and the corrupted data, maybe through some sort of re-normalizing of sensors? (and what exactly is the Ps3 sensor measuring that when corrupted causes an engine roll-back?)
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 five in-flight LOTC events were temporary in that the engine recovered and continued to operate normally for the remainder of the flight.
Is it assumed that the ice melted at altitude after the LOTC event, or was a considerable loss of altitude and descent into warmer air involved?
If the engines were re-started at altitude, does the FADEC ignore the blocked Ps3 signal and the corrupted data, maybe through some sort of re-normalizing of sensors? (and what exactly is the Ps3 sensor measuring that when corrupted causes an engine roll-back?)
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There isn't anything unusual about flying in very cold upper air, but on this occasion, something went dreadfully wrong. It seems that temperatures were exceptionally cold last week, but we have only one accident, so does this low temperature issue really stand up as the cause? Or is there some MEL item involved?
Globules, crystals or something in between?
Solids precipitating out of solution tend to be crystalline, but I'm nowhere near a petroleum chemist and would like to hear from one.
These would normally be the heavier fractions.
Would there be some stratification of the fractions during the flight?
Warming on descent may make the precipitate inclined to stick to fellow particles, somewhat like snow in a cloud.
What is the relative density of the initial precipitate? If lower a froth/slush would form on top, but would there be some 10 tonnes of it at the end of a flight?
If higher, the precipitate as before noted would meet with its fellows at the sumps and intakes. A certain volume of the sumps are generally below the intake to capture contaminants. Once that volume is filled, the stuff goes down the intake.
Too bad the tanks gave way. I suspect the AAIB has collected what samples it could.
The big problem with all of this is that a whole bunch of a/c fueled and flew from Beijing that day and landed without incident. What makes BA038 different?
These would normally be the heavier fractions.
Would there be some stratification of the fractions during the flight?
Warming on descent may make the precipitate inclined to stick to fellow particles, somewhat like snow in a cloud.
What is the relative density of the initial precipitate? If lower a froth/slush would form on top, but would there be some 10 tonnes of it at the end of a flight?
If higher, the precipitate as before noted would meet with its fellows at the sumps and intakes. A certain volume of the sumps are generally below the intake to capture contaminants. Once that volume is filled, the stuff goes down the intake.
Too bad the tanks gave way. I suspect the AAIB has collected what samples it could.
The big problem with all of this is that a whole bunch of a/c fueled and flew from Beijing that day and landed without incident. What makes BA038 different?
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The Ps3/P3b lines and the AD keep being brought up are for the General Electric GE90 engine and not the Trent.
Last edited by gas path; 26th Jan 2008 at 17:40.
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The RR Trent engine has the following pneumatic connections to the EEC:
Pressure transducers in the EEC supply channels A and B
with signals in proportion to the pressure.
P0 - Ambient pressure.
P20 - Fan inlet pressure.
P160 - Fan exit pressure.
P25 - IPC exit pressure.
P30 - HPC exit pressure.
P50 - LPT exhaust pressure.
Pressure transducers in the EEC supply channels A and B
with signals in proportion to the pressure.
P0 - Ambient pressure.
P20 - Fan inlet pressure.
P160 - Fan exit pressure.
P25 - IPC exit pressure.
P30 - HPC exit pressure.
P50 - LPT exhaust pressure.
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Looks like the FAA only focused on GE engines, even though the Trent was specifically mentioned in non-FAA documents as not being immune to a similar condition... here is some germane snips from the prior A/D for PS3 tube issues:
Federal Aviation Administration 14 CFR Part 39
[Docket No. 99-NE-62-AD; Amendment 39-12473; AD 2001-21-03]
RIN 2120-AA64
Airworthiness Directives; General Electric Company GE90 Series Turbofan Engines
...the FAA is especially concerned about the possibility of simultaneous loss of thrust control on both engines due to ice blockage of each engine's Ps3 pressure sensing system under certain atmospheric conditions. Corruption of Ps3 signals could result in simultaneous loss of thrust control of both engines. The unsafe condition description is rewritten for clarification as follows: "The actions specified in this AD are intended to prevent corruption of Ps3 signals, which could result in simultaneous loss of thrust control of both engines."
Remove Reference to P3B Signal Blockage From Unsafe Condition Description
One comment from the manufacturer requests that the unsafe condition statement in the AD be revised to remove P3B signal blockage and partial blockage as some of the causes of loss of engine thrust control. Blockage and partial blockage of the P3B signal could result in a change to the engine acceleration schedule, and possibly a reduction in compressor stall margin, but a loss of thrust control would not occur. The FAA agrees. Reference to P3B signal blockage and partial blockage is removed from the unsafe condition statement in this AD.
http://rgl.faa.gov/Regulatory_and_Gu...4?OpenDocument
http://www8.landings.com/cgi-bin/get...001-21-03.html
NOTES: Addtl info:
Ps3 compressor discharge static pressure, lbf/in2 ~(50-500)
PS3 (or P3 or PT3)= Pressure (& temp) at engine Station 3 (3.0). Compressor discharge pressure.
Both Ps3 and P3B pressure systems incorporate weep holes that allows drainage of water in the lines that may accumulate from condensation or ingested water; however, the field events and the investigation have determined that these design features may not always be effective in eliminating water from these systems. GE is assessing design changes that will prevent water from freezing in these systems and causing corruption of the signals to the FADEC.
Second A/D:
Federal Aviation Administration
14 CFR Part 39 [66 FR 8165 1/30/2001]
[Docket No. 2001-NE-03-AD; Amendment 39-12097; AD 2001-02-12]
RIN 2120-AA64
Airworthiness Directives; CFM International (CFMI) model CFM56-7B Turbofan Engines
AGENCY: Federal Aviation Administration, DOT.
ACTION: Final rule; request for comments.
SUMMARY: This amendment adopts a new airworthiness directive (AD) that is applicable to CFMI model CFM56-7B turbofan engines. This action requires a one-time on-wing torque inspection, and torque if needed, of all the PS3 pressure line fittings to insure proper torque. This amendment is prompted by service events which resulted in two in-flight shutdowns (IFSD’s) and an aborted takeoff due to the disconnection of one of the PS3 line fittings. The actions specified in this AD are intended to prevent air leakage from incorrectly torqued fittings of the PS3 line, which could result in engine power loss.
DATES: Effective February 14, 2001.
Federal Aviation Administration 14 CFR Part 39
[Docket No. 99-NE-62-AD; Amendment 39-12473; AD 2001-21-03]
RIN 2120-AA64
Airworthiness Directives; General Electric Company GE90 Series Turbofan Engines
...the FAA is especially concerned about the possibility of simultaneous loss of thrust control on both engines due to ice blockage of each engine's Ps3 pressure sensing system under certain atmospheric conditions. Corruption of Ps3 signals could result in simultaneous loss of thrust control of both engines. The unsafe condition description is rewritten for clarification as follows: "The actions specified in this AD are intended to prevent corruption of Ps3 signals, which could result in simultaneous loss of thrust control of both engines."
Remove Reference to P3B Signal Blockage From Unsafe Condition Description
One comment from the manufacturer requests that the unsafe condition statement in the AD be revised to remove P3B signal blockage and partial blockage as some of the causes of loss of engine thrust control. Blockage and partial blockage of the P3B signal could result in a change to the engine acceleration schedule, and possibly a reduction in compressor stall margin, but a loss of thrust control would not occur. The FAA agrees. Reference to P3B signal blockage and partial blockage is removed from the unsafe condition statement in this AD.
http://rgl.faa.gov/Regulatory_and_Gu...4?OpenDocument
http://www8.landings.com/cgi-bin/get...001-21-03.html
NOTES: Addtl info:
Ps3 compressor discharge static pressure, lbf/in2 ~(50-500)
PS3 (or P3 or PT3)= Pressure (& temp) at engine Station 3 (3.0). Compressor discharge pressure.
Both Ps3 and P3B pressure systems incorporate weep holes that allows drainage of water in the lines that may accumulate from condensation or ingested water; however, the field events and the investigation have determined that these design features may not always be effective in eliminating water from these systems. GE is assessing design changes that will prevent water from freezing in these systems and causing corruption of the signals to the FADEC.
Second A/D:
Federal Aviation Administration
14 CFR Part 39 [66 FR 8165 1/30/2001]
[Docket No. 2001-NE-03-AD; Amendment 39-12097; AD 2001-02-12]
RIN 2120-AA64
Airworthiness Directives; CFM International (CFMI) model CFM56-7B Turbofan Engines
AGENCY: Federal Aviation Administration, DOT.
ACTION: Final rule; request for comments.
SUMMARY: This amendment adopts a new airworthiness directive (AD) that is applicable to CFMI model CFM56-7B turbofan engines. This action requires a one-time on-wing torque inspection, and torque if needed, of all the PS3 pressure line fittings to insure proper torque. This amendment is prompted by service events which resulted in two in-flight shutdowns (IFSD’s) and an aborted takeoff due to the disconnection of one of the PS3 line fittings. The actions specified in this AD are intended to prevent air leakage from incorrectly torqued fittings of the PS3 line, which could result in engine power loss.
DATES: Effective February 14, 2001.
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RBF: Good questions. I was an analytical chemist for about 20 years up to the 90's - all over the world, and have done many assays of Jet A-1. If you run through the last thread and look at the discussion between Tubby Linton, myself and Moggiee, (before the latest AAIB report) you pretty much have it. It was so crashingly obvious to all of us then and it is even more obvious now that the 8 seconds differential has been revealed. The incident was fuel and temperature related and if you look at Belgiques' post I think he's more or less got it right (can we call them wax crystals, not globules, because they have the behaviour of crystals).
If you live in the UK you will know that if you have water running through a pipe, it is unlikely to freeze. You also know that if your pipe to your sink goes outside before coming inside again, when you open the tap, you will get a small spurt of water...then nothing or a trickle. If that trickle is left for long enough, then the ice in the pipes melts and you get flow back again.
Wax crystals form easily but it takes an increase in temperature and also motion to resolubilize them. There was sufficient fuel flow during cruise to prevent blockage (ice,wax, or both). during the decent, there was not.
When the increase in thrust was commanded, there was initially enough fuel to cause a small increase in thrust, then there was not. There was insufficient time to resolubilize the crystals during the decent.
It doesn't necessarily mean - in fact its unlikely - that the fuel was off-spec by the way. If I am right, this may be a landmark event that forces a re-evaluation of Jet A/A1 specs. If I am wrong, I promise to kiss Dannys left buttock.
Pinkman
If you live in the UK you will know that if you have water running through a pipe, it is unlikely to freeze. You also know that if your pipe to your sink goes outside before coming inside again, when you open the tap, you will get a small spurt of water...then nothing or a trickle. If that trickle is left for long enough, then the ice in the pipes melts and you get flow back again.
Wax crystals form easily but it takes an increase in temperature and also motion to resolubilize them. There was sufficient fuel flow during cruise to prevent blockage (ice,wax, or both). during the decent, there was not.
When the increase in thrust was commanded, there was initially enough fuel to cause a small increase in thrust, then there was not. There was insufficient time to resolubilize the crystals during the decent.
It doesn't necessarily mean - in fact its unlikely - that the fuel was off-spec by the way. If I am right, this may be a landmark event that forces a re-evaluation of Jet A/A1 specs. If I am wrong, I promise to kiss Dannys left buttock.
Pinkman
Last edited by Pinkman; 26th Jan 2008 at 19:18.
We are getting there. I go for today's Daily Mail theory. As an ex 744 jockey who has flown many sectors over Siberia in the winter and have had numerous eicas warnings of low fuel temp, I reckon this combined with possible contaminated fuel from Beijing and a low power descent would cause waxing/icing of fuel. I don't believe there was anything wrong with the computers and everything else seems to have been ruled out so my opinion is contaminated fuel. See, I didn't even get technical.
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re. fuel/oil heat exchanger?
How does it work? A diagram posted here shows this heat exchanger in the path from the fuel tank to the engine. Does the engine rely on the fuel being warmed up at that point, and if so, is there an additional constraint due to the possibility (?) of the oil being cooled too much? Also what is the reason for the design asymmetry between the L and R fuel paths?
I understand that the 777 has jet pumps in the tanks, if so the fuel is continually circulated. Jet pumps are supplied with fuel from the tank pump and passed through a venturi which draws fuel from that part of the tank and sends it towards the main pump and prevents build up of any solids.
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Does anybody know of a site that can do an historic analysis of flights leaving from Beiging on the same day as BA38? We could be fairly sure that many would have been refueled with the same batch of fuel. Where did they leave to? I would be surprised if there were not some flights that flew flight paths to destinations somewhat colder than UK. The fact that they obviously did not all crash would not rule anything in or out, but such data that can be gleaned from the departing flights might add a little to the overall picture.
I've looked at the Beiging airport site, but it contains no historical data.
I've looked at the Beiging airport site, but it contains no historical data.
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The section on fuel temperature in go-si's link is informative
http://www.boeing.com/commercial/aer...lar_story.html
If after reading that, you still think its a 'load of tosh' then there is not more that can be added.
A380focal: 'nice and toasty'. Again: to what temperature (Skin, TAT, OAT, whatever)?
Pinkman
http://www.boeing.com/commercial/aer...lar_story.html
If after reading that, you still think its a 'load of tosh' then there is not more that can be added.
A380focal: 'nice and toasty'. Again: to what temperature (Skin, TAT, OAT, whatever)?
Pinkman