BA038 (B777) Thread
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High-impedance parts . . .
If a PED had interfered with the high-impedance parts of a circuit that controlled a relay, then I could see it, but by the fact that we are talking about relays acting on their own I assume that has been ruled out
Could fretting corrosion in connectors be a factor in this case? This kind of corrosion is often not visible to the naked eye. That is why there is an occasional misperception that there is no corrosion problem.
This was found to be a factor in the case regarding unscheduled closing of the shutoff valve i referred to in previous posts.
Regards,
Green-dot
Micro-muck
This is air pollution muck - NSEU - and its sink rate is very low within its water carrier.
Thanks for the 400Kg/hr figure. I was wondering how 'leisurely' the scavenge was.
If a dam of ice released a cascade of clean water into the water scavenge area, would 400kg/hr of water be enough to slow the engine? If so, the case against the dirty snowman collapses, and 'my' finger points to ice in the fuel.
Thanks for the 400Kg/hr figure. I was wondering how 'leisurely' the scavenge was.
If a dam of ice released a cascade of clean water into the water scavenge area, would 400kg/hr of water be enough to slow the engine? If so, the case against the dirty snowman collapses, and 'my' finger points to ice in the fuel.
Yes, 777fly, my outsider's view is showing its weaknesses.
The increase in volume of 4000Kg (about 320 - correction - 5000 litres) can only be supplied by adiabatic expansion if there is enough air in the tank to start with. If there is enough then there should be no contamination in the climb.
Edit3 - hope I'm on better form today ...
Tank capacity 100K litres, fuel upload approx 25k litres. Air to be expanded 75k litres. Expansion needed to replace fuel spent in the climb 5k litres. Estimate about 100mB (adiabatic) pressure change or 3000ft. There is an order of magnitude more air than needed to replace the fuel burned.
(OK - you professionals knew all this - I'm conceding as graciously as I can!)
Are the occasional 'water-in-fuel' warnings spurious? If not, 100+ gallons of water (and associated pollutants depending on where it came from) gets in some how.
NSEU may have exonerated the dirty snowman with his 400kg/hour scavenge rate for clean water. Could that cause the problem?
The increase in volume of 4000Kg (about 320 - correction - 5000 litres) can only be supplied by adiabatic expansion if there is enough air in the tank to start with. If there is enough then there should be no contamination in the climb.
Edit3 - hope I'm on better form today ...
Tank capacity 100K litres, fuel upload approx 25k litres. Air to be expanded 75k litres. Expansion needed to replace fuel spent in the climb 5k litres. Estimate about 100mB (adiabatic) pressure change or 3000ft. There is an order of magnitude more air than needed to replace the fuel burned.
(OK - you professionals knew all this - I'm conceding as graciously as I can!)
Are the occasional 'water-in-fuel' warnings spurious? If not, 100+ gallons of water (and associated pollutants depending on where it came from) gets in some how.
NSEU may have exonerated the dirty snowman with his 400kg/hour scavenge rate for clean water. Could that cause the problem?
Last edited by Rightbase; 4th Mar 2008 at 16:13. Reason: 1.dumb arithmetic mistake 2.inability to count zeros 3.more info
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I think we should all remember that the scavenge system does not feed the remains of the center tank directly into the main tank boost pump pickups but rather it stirs up the fuel around the pickup.
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If a PED had interfered with the high-impedance parts of a circuit that controlled a relay, then I could see it, but by the fact that we are talking about relays acting on their own I assume that has been ruled out
Could that possibly mean high-impedance parts or connections in the wiring close to the relays somewhere between the relays and ELMS?
Could that possibly mean high-impedance parts or connections in the wiring close to the relays somewhere between the relays and ELMS?
Just toying with ball-park figures, but imagine a relay with a 28 volt coil. Number of turns required would result in around 1mH inductance and a self-resonant frequency around 1MHz.
What sort of field strength at 1 MHz would be needed to induce 3 watts in the coil??
P (dBm) = E (dBuV/m) - 20log F + Antenna gain - 77,2
Putting the relay coil and associated wiring as a 0 gain antenna and Power as 34 dBm the required field is 111 dBuV/m, or less than 1 V/m.
Do medium wave transmitters still exist?
According to the diagram provided in an earlier post (sorry - can't find it at the moment) the centre tank fuel scavenge outlet is at the outboard (high) end of the main tank. To get to the engines any water scavenged from the centre tank at this stage has to find its way back down to the main tank water scavenge pump which moves it to near the boost pump inlet.
(see post 461 Page 24 )
(see post 461 Page 24 )
Last edited by Rightbase; 5th Mar 2008 at 20:26. Reason: Found it!
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pump cavitation
Pump output can be greatly diminished by cavitation and would give the results seen in this case.
The HP gear pumps show evidence of cavitation. Two of the principle determinants for the point at which cavitation occurs are pump speed and fluid viscosity.
A mixture of hydrocarbons such as jet fuel can have a temperature dependent change of viscosity while in the liquid state.
Cold high viscosity fuel along with an increase in pump speed at thrust demand may have lead to the cavitation.
Fuel that was not frozen but chilled to a high viscosity would have flowed through the large surface area filters without producing an alarm. And the boost pumps may have handled it without a problem too.
But how and why did it happen on this flight and not so many other flights?
I look back to a post on the previous thread (pg 20, post 394, by Glueball)
http://www.pprune.org/forums/showthr...310013&page=20
"The temperature probes in the 747-400, 777, and MD-11 are located where the bulk of the fuel is coldest. However, some fuel may be colder than the fuel measured by the probes, such as the fuel that is in contact with the lower wing skin. This creates a temperature gradient in the fuel tank from the wing skin to the location of the probe.
As fuel travels to the boost pump inlets, the bottom, cold layer flows through small flapper valves located on solid tank ribs next to the bottom wing skin. These valves are used to control fuel slosh. Thus, the cold fuel tends to flow toward the boost pump inlets."
Speculation ...
This flight started with fuel from a location that had cold weather. The initial FL resulted in a cold soak. The original flight plan was prudent for the conditions expected. The crew elected to honor a request from ATC to climb to FL348, ambient temperature approximately -65ºC. This was followed by a climb to FL380, -76C.
It seems to me that there was an extreme gradient between the coldest side of the tank and the fuel probe. While the the bulk of the fuel remained above the min. temp, I think that along the tank side, the fuel was chilled to the point that it congealed on the tank surface. Maybe it was still not frozen but perhaps so high in viscosity that it no longer moved with fuel currents to be remixed.
Once the tank surface warmed at arrival this high viscosity fuel would be released to flow toward the boost pump. Since the temp probe is not located at the pump inlet, it may have never seen this cold spot in the fuel.
Holes in the cheese ...
To reproduce this you have to cold soak the fuel. Expose the tank to extreme cold to get the required gradient, tank to probe, otherwise the crew will see the problem and correct for it. On arrival, a little more fuel in the tanks and the currents might not direct the cold spot to the pump or less fuel and the sloshing of flight maneuvers might remix the fuel. And the timing has to be just right. Early release of the cold spot gives a greater time for the remix of the fuel. A late release and the plane is on the ground before the cold spot gets to the pumps.
On this flight it all lined up. And it's going to be hell to prove. I bet it's a long time before we see a final report.
The HP gear pumps show evidence of cavitation. Two of the principle determinants for the point at which cavitation occurs are pump speed and fluid viscosity.
A mixture of hydrocarbons such as jet fuel can have a temperature dependent change of viscosity while in the liquid state.
Cold high viscosity fuel along with an increase in pump speed at thrust demand may have lead to the cavitation.
Fuel that was not frozen but chilled to a high viscosity would have flowed through the large surface area filters without producing an alarm. And the boost pumps may have handled it without a problem too.
But how and why did it happen on this flight and not so many other flights?
I look back to a post on the previous thread (pg 20, post 394, by Glueball)
http://www.pprune.org/forums/showthr...310013&page=20
"The temperature probes in the 747-400, 777, and MD-11 are located where the bulk of the fuel is coldest. However, some fuel may be colder than the fuel measured by the probes, such as the fuel that is in contact with the lower wing skin. This creates a temperature gradient in the fuel tank from the wing skin to the location of the probe.
As fuel travels to the boost pump inlets, the bottom, cold layer flows through small flapper valves located on solid tank ribs next to the bottom wing skin. These valves are used to control fuel slosh. Thus, the cold fuel tends to flow toward the boost pump inlets."
Speculation ...
This flight started with fuel from a location that had cold weather. The initial FL resulted in a cold soak. The original flight plan was prudent for the conditions expected. The crew elected to honor a request from ATC to climb to FL348, ambient temperature approximately -65ºC. This was followed by a climb to FL380, -76C.
It seems to me that there was an extreme gradient between the coldest side of the tank and the fuel probe. While the the bulk of the fuel remained above the min. temp, I think that along the tank side, the fuel was chilled to the point that it congealed on the tank surface. Maybe it was still not frozen but perhaps so high in viscosity that it no longer moved with fuel currents to be remixed.
Once the tank surface warmed at arrival this high viscosity fuel would be released to flow toward the boost pump. Since the temp probe is not located at the pump inlet, it may have never seen this cold spot in the fuel.
Holes in the cheese ...
To reproduce this you have to cold soak the fuel. Expose the tank to extreme cold to get the required gradient, tank to probe, otherwise the crew will see the problem and correct for it. On arrival, a little more fuel in the tanks and the currents might not direct the cold spot to the pump or less fuel and the sloshing of flight maneuvers might remix the fuel. And the timing has to be just right. Early release of the cold spot gives a greater time for the remix of the fuel. A late release and the plane is on the ground before the cold spot gets to the pumps.
On this flight it all lined up. And it's going to be hell to prove. I bet it's a long time before we see a final report.
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Code One . . . .
After digging into some background information i ran into an article in a "Code One Magazine" which may be of interest. Although a totally different type of aircraft, the article deals with a ground test to simulate a certain failure in the fuel system of a F-16. The similarity with the subject T7 is that its engine is also electronically controlled and the result of a simulation, engine rollback, comes remarkably close to what was experienced on G-YMMM. I know, totally different aircraft types but engine response seems not so different. Please read on . . . .
In this simulation the writer of the article, a senior experimental test pilot, describes the following:
Quote:
"Recently, I saw how the engine would quit in other than the normal airstart-test type of atmosphere. Although these tests were accomplished on the ground, I saw several things that I hadn't seen before, things I'd like to pass along. You can never know too much about the airplane.
I am sure that you are aware that there have been some as yet unexplained flameouts with the F110 engine. What we attempted to do was to try to induce as many potential malfunctions in the airplane as possible in order to shed some light on some of the past accidents/incidents. The airplane was tied down in the normal manner and then fully instrumented to record all the parameters of interest.
One large impression that I had was how tenaciously the engine will cling to life if it has fuel. On one test, we had artificially closed the master fuel shutoff valve to only five percent of capacity, that is, ninety-five percent closed. (There is no way that you can do this in your airplane without some really weird failure, or a plumbing change like we had for the purposes of this test.) The boost pumps were off and the refueling door was open so the system was depressurized. The engine was in idle and running just fine. The test point called for me to snap-accel the engine to ninety-five percent. The engine only briefly touched ninety-five percent, immediately rolled back to ninety-two percent, and hesitated there for a few seconds. It then rolled back to about eighty-seven percent for a few seconds. Subsequently it flamed out, but had an automatic restart accomplished in time to catch the rpm at eighty percent. It stayed there for another few seconds, and then flamed out again. The engine then auto-transferred to secondary engine control, or SEC, and got another auto restart at seventy-two to seventy-three percent. It maintained this condition for a little while and then flamed out again, with an auto restart in SEC at about sixty-five percent where it stayed for a while and then slowly continued to decay toward zero rpm. From this, and other similar runs, I feel that if the engine is operating properly, you have little fear of its quitting as long as the aircraft is providing fuel." Unquote
The article was written in 1990.
Here is the link to the complete article:
http://www.codeonemagazine.com/archi...out/index.html
In the simulation above it was elected to close the main shutoff valve for 95 percent, only 5 percent capacity, and the engine managed to retain RPM above idle several times for "a little while", even with boost pumps off and the fuel system depressurized (air refuel door open).
Focussing on the T7 dual engine roll back again, just suppose both spar valves had temporarily closed for, say, 80 percent (only 20 percent capacity remaining) with boost pumps on. Could that have resulted in engine roll backs to a stabilized thrust level above flight idle and cause cavitation at the engine pumps as the engines initially responded and then rolled back because reduced fuel flow did not meet engine demand?
I assume similar simulations such as mentioned above would have to be performed to find answers or are there other means (computer simulations?) to observe engine behaviour under such conditions?
Regards,
Green-dot
In this simulation the writer of the article, a senior experimental test pilot, describes the following:
Quote:
"Recently, I saw how the engine would quit in other than the normal airstart-test type of atmosphere. Although these tests were accomplished on the ground, I saw several things that I hadn't seen before, things I'd like to pass along. You can never know too much about the airplane.
I am sure that you are aware that there have been some as yet unexplained flameouts with the F110 engine. What we attempted to do was to try to induce as many potential malfunctions in the airplane as possible in order to shed some light on some of the past accidents/incidents. The airplane was tied down in the normal manner and then fully instrumented to record all the parameters of interest.
One large impression that I had was how tenaciously the engine will cling to life if it has fuel. On one test, we had artificially closed the master fuel shutoff valve to only five percent of capacity, that is, ninety-five percent closed. (There is no way that you can do this in your airplane without some really weird failure, or a plumbing change like we had for the purposes of this test.) The boost pumps were off and the refueling door was open so the system was depressurized. The engine was in idle and running just fine. The test point called for me to snap-accel the engine to ninety-five percent. The engine only briefly touched ninety-five percent, immediately rolled back to ninety-two percent, and hesitated there for a few seconds. It then rolled back to about eighty-seven percent for a few seconds. Subsequently it flamed out, but had an automatic restart accomplished in time to catch the rpm at eighty percent. It stayed there for another few seconds, and then flamed out again. The engine then auto-transferred to secondary engine control, or SEC, and got another auto restart at seventy-two to seventy-three percent. It maintained this condition for a little while and then flamed out again, with an auto restart in SEC at about sixty-five percent where it stayed for a while and then slowly continued to decay toward zero rpm. From this, and other similar runs, I feel that if the engine is operating properly, you have little fear of its quitting as long as the aircraft is providing fuel." Unquote
The article was written in 1990.
Here is the link to the complete article:
http://www.codeonemagazine.com/archi...out/index.html
In the simulation above it was elected to close the main shutoff valve for 95 percent, only 5 percent capacity, and the engine managed to retain RPM above idle several times for "a little while", even with boost pumps off and the fuel system depressurized (air refuel door open).
Focussing on the T7 dual engine roll back again, just suppose both spar valves had temporarily closed for, say, 80 percent (only 20 percent capacity remaining) with boost pumps on. Could that have resulted in engine roll backs to a stabilized thrust level above flight idle and cause cavitation at the engine pumps as the engines initially responded and then rolled back because reduced fuel flow did not meet engine demand?
I assume similar simulations such as mentioned above would have to be performed to find answers or are there other means (computer simulations?) to observe engine behaviour under such conditions?
Regards,
Green-dot
Last edited by Green-dot; 5th Mar 2008 at 19:43. Reason: Spelling and additional questions.
Change in procedures ?
Despite the lack of conclusive evidence in this case does anyone know if BA, or any other 777 operator has changed any procedures in the wake of this accident, and what that change might consist of ?
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Blood tested?
Would people expect the BA crew to have their blood / fat tested after such an incident?
I have just started a thread on this subject which has been 'kindly' moved to Ground & Other Ops Forums - Questions! Thanks guys.
I have just started a thread on this subject which has been 'kindly' moved to Ground & Other Ops Forums - Questions! Thanks guys.
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Vapour lock, not Carb-ice.
I may have been concentrating too much on the waxing and ice effects of very low outside temps during cruise .
...We are advised the uplifted fuel (stored and delivered at subzero temp) exceeded specs by a long chalk . being non waxing at temps down to -57 instead of only the normally expected -47ish
...The Chinese gave us a blend specially suited to their expected ISA minus 20 or worse. Its like our road fuel we get a more volatile blend in the winter.
...But how was this blend achieved? Was it just a generally lighter distillate? or was it by adding a much more volatile "additive"? With motor fuel it might be "quickstart" or alcohol.
.. The uplift was mostly in the CTW tank with the Wing tanks topped off.Fuel management in flight used a large proportion of the uplift at first., the remainder mixing with and somewhat diluting the original wing tank fuel.
...Finally descending into warmer UK temps at LHR, did this volatile cause gassing, cavitation, and loss of fuel pump efficiency when an extra demand reduced manifold pressures on the suction side of the pumps?
...We are advised the uplifted fuel (stored and delivered at subzero temp) exceeded specs by a long chalk . being non waxing at temps down to -57 instead of only the normally expected -47ish
...The Chinese gave us a blend specially suited to their expected ISA minus 20 or worse. Its like our road fuel we get a more volatile blend in the winter.
...But how was this blend achieved? Was it just a generally lighter distillate? or was it by adding a much more volatile "additive"? With motor fuel it might be "quickstart" or alcohol.
.. The uplift was mostly in the CTW tank with the Wing tanks topped off.Fuel management in flight used a large proportion of the uplift at first., the remainder mixing with and somewhat diluting the original wing tank fuel.
...Finally descending into warmer UK temps at LHR, did this volatile cause gassing, cavitation, and loss of fuel pump efficiency when an extra demand reduced manifold pressures on the suction side of the pumps?
wilyflier:
Quote: " The uplift was mostly in the CTW tank with the wing tanks topped off".
This could not be the case. The aircraft would have arrived with, at a guess, 15000kgs (total) in the wings, assuming that there was no tankering. During refuelling the wing tanks have to be completely full before any fuel goes in to the centre tank. As the total wing tank capacity is about 58,000kgs, about 21500 kgs would have been put into each wing tank. The aircraft left with 79000kgs onboard, so about 21000kgs must have gone into the centre tank. In other words roughly the same amount of fuel was uplifted into each tank.
Quote: " The uplift was mostly in the CTW tank with the wing tanks topped off".
This could not be the case. The aircraft would have arrived with, at a guess, 15000kgs (total) in the wings, assuming that there was no tankering. During refuelling the wing tanks have to be completely full before any fuel goes in to the centre tank. As the total wing tank capacity is about 58,000kgs, about 21500 kgs would have been put into each wing tank. The aircraft left with 79000kgs onboard, so about 21000kgs must have gone into the centre tank. In other words roughly the same amount of fuel was uplifted into each tank.
Last edited by 777fly; 4th Mar 2008 at 13:08. Reason: spelling
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Fat test - why?
Cats Five - Fat is the long term storage place in your body for all the nasties that enter it either deliberately or by accident.
27 airline pilots were checked by UCL in 2006 and each and every one of them had abnormal amounts of toxic chemicals in them, which in turn produce mind bending effects.(sic)
Why not check for it as it could be relavent evidence and more importantly, it shouldn't be there.
DB
27 airline pilots were checked by UCL in 2006 and each and every one of them had abnormal amounts of toxic chemicals in them, which in turn produce mind bending effects.(sic)
Why not check for it as it could be relavent evidence and more importantly, it shouldn't be there.
DB