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I work in business systems IT and not in any aviation based profession
Given that they've still been unable to find any indication of a mechanical fault yet this is something significant enough to affect both engines, what do you guys think are the chances of this being a software problem ? |
(apparently) not a software problem
From the AAIB's statements on the functioning of the aircraft systems, it appears that all software systems in the Autothrottle and EEC's (and elsewhere) functioned as expected
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Would even 4 engines have done the same.....?
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Mmm! pulling the fire handles at 700 ft. Now would that have the same affect?
Actually I see from other posts that the QAR did not record the last 45 secs. But I guess the FDR would have. So am just wondering when the handles got pulled. After it came to a halt I guess, interesting senario on the post impact fuel spill. I'll go back under me rock.:confused: |
It is really surprising to see that both engines lost power at (almost) the same time, and in addition, they both came to same low RPM (above flight idle). In case of ice obstruction, it's already quite unlikely to expect a simultaneous event, but how can it lead to a similar low thrust setting on both engines ???
It means both ice obstructions did let a similar leak on both sides...:bored: Correct me if I'm wrong, but up to now, it's only the indicated fuel quantity that was reported, not the actual fuel found in the wreckage... I just want to remind that Tunintair had a fuel exhaustion accident while indications were showing adequate fuel on board... Is it really impossible to consider low fuel conditions causing the cavitation in high pitch attitude ? |
I'm wondering if there's a fuel pressure transducer downstream of the metering valves and if so, was the fuel pressure logged.
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Hi Topslide6,
thanks for the comment. I just like to stress that I'm not blaming the crew in any way here. The situation was apparently so extraordinary that one can't realistically expect more. |
Fuel quantity..
sispanys ria,
You are right - only the indicated fuel quantity is mentioned in the report, but the report also mentions that samples have been taken from the 2 wing tanks. Later in the report the following statement is given: A test of the fuel quantity processor unit (FQPU) was satisfactory and its non-volatile memory did not reveal any defects stored prior to the accident. |
Originally Posted by sispanys ria
(Post 3923086)
Correct me if I'm wrong, but up to now, it's only the indicated fuel quantity that was reported, not the actual fuel found in the wreckage...
I just want to remind that Tunintair had a fuel exhaustion accident while indications were showing adequate fuel on board... Is it really impossible to consider low fuel conditions causing the cavitation in high pitch attitude ? Re: water/other fuel contamination - there wasn't any. The AAIB report makes fascinating reading. I highly recommend it. |
avrflr i'm sorry you cannot post a polite reply. I'm just interrogating myself, and never mentioned fuel exhaustion, but in a low fuel configuration, it might have been possible that the tank LP pumps were not able to provide the adequate fuel to the HP pumps...
As you refer to the small items found in the tanks, I would like to see how you explain that almost simultaneously, two different items would have reduced two fuel flows to two similar values on both engines... |
The thing had ten tonnes of fuel on board. There was no low fuel state. None. Ever.
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Water and ice cristals are normal into the airliners tanks,and comes with the air that vent tanks entering by the NACA inlets near the wing tips,not during refueling.
Also,to much debriss to block both booster pumps per wing tank...the engine fuel feed lines in the 777 are about 3 inches diameter. |
Originally Posted by sispanys ria
(Post 3923191)
avrflr i'm sorry you cannot post a polite reply. I'm just interrogating myself, and never mentioned fuel exhaustion, but in a low fuel configuration, it might have been possible that the tank LP pumps were not able to provide the adequate fuel to the HP pumps...
As you refer to the small items found in the tanks, I would like to see how you explain that almost simultaneously, two different items would have reduced two fuel flows to two similar values on both engines... I can't explain how the accident happened, but then neither can the AAIB at the moment and they do this for a living. They are not stupid or corrupt, if the answer was simple, like low fuel or contaminated fuel, they would have told us on day 1. |
gerry foley
Gerry, you are reading my post literally. Replace 'post - event' with 'after the event' and you will see what I am trying to say: "how can you tell, from the evidence, when you look at the impeller after the event, that cavitation, which is a transient phenomenon, has actually occurred". Apologies for my clumsy british english phrasing:E. And the answer was given above by several people: pitting, damage, caused by huge pressure forces and detonation.
But despite all the slightly sarcastic comments to my earlier post no one has answered my question: If it isnt ice, wax, or water, what other common mode control law reduced one engine seven seconds after the other? I still refuse to believe that there is 100% independant authority and segregation between the two engines at all times and that there is never ever a point or situation at which the two engines in a modern aircraft with digital engine and fuel management controls have the function to compare thrust and balance accordingly. I just cant believe that you guys have to either continually adjust throttles to compensate for small variations in thrust between engines or use rudder trim to keep a constant heading (eg in the cruise)? How fuel inefficient that would be. There must at some point and in some flight modes be a digital comparison between the thrust produced in each engine and my question is still, is there concievably a flight mode or condition such that when one engine unexpectedly loses power (eg if fuel feed blocked by a red plastic scraper) the other engine is electronically limited to avoid... well you tell me. There must be a 777 sparky out there who has the FADEC decision logic. Otherwise, there's only one explanation.. different pieces of crud left behind in different wings just happened to block respective fuel filter screens just seconds apart. I dont believe that and neither do you... |
AAIB Report
My reading was that the Fuel was "in Spec". Is that "within Spec" for pure Fuel or does that consider that there is no "Spec" for Water, Alcohol, Glycol, or Canal Mud? I'd like to see collection protocol, transit, and testing methods before I defend the FUEL. (As in, what reality offered in the way of combustible supply to RR1 and RR2.) Just Sayin'.
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Originally Posted by Topslide6
I must admit, my initial response on hearing about this was that it was probably to do with FADEC or the 777 equivilent. However, on reflection I would have said it's highly unlikely, but still possible. With the certification process these aircraft go through, and how many commercial flights the 777 has done to date, the laws of probability would dictate that it ought to have manifested itself by now.
The certification process and 3.6 million flight hours says virtually nothing about manifestation of SW faults. For an example, consider that the certification process and a large percentage of those flight hours failed to discover a significant bug in the flight control SW that manifested itself first in August 2005 out of Perth. PBL |
Continuing to defend the fuel
Originally Posted by airfoilmod
(Post 3923306)
My reading was that the Fuel was "in Spec". Is that "within Spec" for pure Fuel or does that consider that there is no "Spec" for Water, Alcohol, Glycol, or Canal Mud? I'd like to see collection protocol, transit, and testing methods before I defend the FUEL. (As in, what reality offered in the way of combustible supply to RR1 and RR2.) Just Sayin'. #124, #125
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I'm with Avrflr
As an ex-fuel guy, if they've sampled properly, and actually taken a sample down to the worst case temperature and its OK, then its not fuel - period. And hopefully none of you - especially Danny - will remember what I offered to do if I was wrong in asserting it was waxing.
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Start
I don't think I'm committing what I deplore. A conclusion of any kind is premature, speculation never is. Having been tested, the Fuel, to me, remains to be exonerated. Speculation, by its very nature, could lead to incrimination, which is silly at this point. My retort had naught to do with clever chaps, but ill advised exoneration of any procuring cause, which the chaps have not done, and someone, I think, thinks they have.
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You must know something about fuel that I don't. If testing won't exonerate it, what will?
I'm all for speculation, but let's have hypotheses that don't require me to believe that the AAIB are morons. Or that jet fuel has acquired some hitherto undiscovered properties that can't be revealed by fuel testing laboratories. |
Pinkman,
You say:
"is there concievably a flight mode or condition such that when one engine unexpectedly loses power (eg if fuel feed blocked by a red plastic scraper) the other engine is electronically limited to avoid... well you tell me." The answer to this is a NO! Such a feature does not make any sense - imagine what would happen in a takeoff with one engine failing! Whether the engines on the 777 are digitally connected, I do not know . I have flown B767 and A340, and these aircraft types have digital connections between their engines. |
Keep thinking
The Final Report is the one to read. I'm not trying to be coy, the fuel that made its way to the Lab seems to have tested well, within Spec. No argument with that. What's missing is unfortunate. Exact position of Throttle Levers? AOA? Exact temperature of mixture entering LP and HP Pumps? How long Mixture "cavitated"? Where is the liquid (Sic) that transited out the hot end? Indeed, where is the material that hasn't been subjected to "tests". Post incident, there remains a percent accuracy for any test performed having to do with all systems. Without testing ALL the remnants of the tankage, no result is foolproof. These are dedicated professionals, who do excellent forensic work who also happen to be under a huge Microscope. From what's been released, either the throttle settings sequentially slipped to low thrust positions, or Quantity, Quality of Fuel was compromised. Turbofans are not terribly complicated; pump fuel, they provide thrust at very predictable levels. Withold fuel, they reduce output.
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New software revision had been installed in December. I think it was a FADEC revision.
The accident is a puzzle. Software has not been ruled out by the AAIB(based of FAA letter Jan 29, 2008). |
The problem with trying to attribute the fault to the FADEC (EEC) is that the report states that the metering valves operated correctly in response to the loss of thrust and opened. so the EEC worked. The thrust lever position was correct. This is either fuel or fuel flow or as a friend at work postulated today a large bubble of no oxygen air on the approach.
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Quote :-
.............. Data, downloaded from the Electronic Engine Controllers (EECs) and the QAR, revealed no anomalies with the control system operation. At the point when the right engine began to lose thrust the data indicated that the right engine EEC responded correctly to a reduction in fuel flow to the right engine, followed by a similar response from the left EEC when fuel flow to the left engine diminished. Data also revealed that the fuel metering valves on both engines correctly moved to the fully open position to schedule an increase in fuel flow. Both fuel metering units were tested and examined, and revealed no pre-existing defects. ..........unquote A question - IF, repeat IF, the fuel is o.k., the EEC commands were correct, the pumps, filters, etc... worked o.k. - then what is left ? One thing I don't think is properly mentioned (?) is the ACTUAL operational records of the fuel pumps. Yes, they were tested afterwards and considered capable of working at full capacity, however, I PRESUME that they are variable speed, so would the speed that they were ordered to work at and that they actually worked at be recorded anywhere ? . |
One thing I don't think is properly mentioned (?) is the ACTUAL operational records of the fuel pumps. Yes, they were tested afterwards and considered capable of working at full capacity, however, I PRESUME that they are variable speed, so would the speed that they were ordered to work at and that they actually worked at be recorded anywhere ? |
Quote from #112:
Now in no way am I suggesting that on this 777 the generators magically re-connected themselves in flight. However sudden low pressure from all LH & RH pumps could (in theory) occur if the phase relationship of the power supply to all of the pumps suddenly changed. Also, if the 777 is anything like the Fokker 100, it might only be the fuel pumps that would have a problem with this. How that might happen in practice I don't know - I would think it so unlikely as to be almost impossible. Also, even if it did happen, I would be surprised if such a loss of pressure starved the engines - but perhaps in combination with other things it is (theoretically) possible. Suppose that the APU startup was actually the cause of the problem - Is it possible this was started by accident or automatically started and this messed up the electrical phasing? |
Private Eye - 22 February
Interesting article in the back pages of the Eye this issue. For those who are not familiar with the Eye, it is a satirical magazine, but the last few pages tend to be reserved for more thoughtful writing. Article below, complete:
"A Software Triple Whammy Air accident investigators have provisionally identified the cause of last month's British Airways Boeing 777 crash at Heathrow as a failure by both engines to provide the necessary thrust of power ahead of landing, causing it to fall short of the runway. Why both engines shoud fail to respond ro demands from the "Auto throttle" and then from the two pilots is not yet known, but investigators are looking closely at the craft's computer systems. And so they should; aircraft and computer experts warned long ago of a potentially dangerous flaw in the software driving the 400-seater's three primary flight computers (PFCs). Until the revolutionary 777 (dubbed the "computer with wings"), every passenger jet had a failsafe "triplex" system of PFCs - three computers from three different companies with three different teams writing the software. One computer would fly the aircraft, one would monitor and take over if a problem occurred and the third would be in reserve. A mistake in one was very unlikely to be in the second, and even more unlikely in the third. Thus safety in a craft that was to take autopilot to a new level was all but guaranteed. So it was - at first - with the 777. Boeing took its proposals for a triplex PFC to the Federal Aviation Administration (FAA) which gave approval. But then things started to unravel. Without putting the software programme out to competitive tender, Boeing appointed GEC Marconi, based in Rochester, Kent, as sole writer. GEC had three different teams of software writers, separated by "chinese walls". According to Boeing itself, however: "It became apparent that the three separate teams were having to ask Boeing so many questions for clarification that the independence of the three teams was irreparably compromised". So instead of hiring new teams, which would have delayed the project and may have rendered Boeing liable for penalty payments, the three teams became one. Triplex was forgotten. The result was 132,000 lines of software code, unprecedented in aviation history, which, it seems, could not be independently checked. The then chairman of the British Computer Society's safety critical systems taskforce, Professor Brian Wichmann, told Computer Weekly magazine (which revealed the potential flaw back in 1995) that "more than 20,000 lines of code are too complex to test" and that 132,000 lines of code were impossible to verify. If a bug or glitch caused a failure during a take off or landing, the plane could crash before the pilot had time to react. But the system was approved, not by the FAA or the British Civil Aviation Authority (CAA), but by the European Joint Airworthiness Authorities (JAA) based in Holland - by just three JAA specialists. As the certifying authority in America , the FAA asked for more comprehensive software audits, but then accepted Boeing's argument that the lines of code had already been tested and verified so extensively that any potential for error had been ruled out. Mary Schiavo, the former director-general at the US Department of Transportation, revealed in her book "Flying Blind, Flying Safe" that the FAA's national software expert later admitted to her: "I'm in a very embarrassing position. To say that the software is safe, I can't tell you that. I can tell you that the software development has followed our procedures". So that's all right, then. Air accident investigators say that they are focusing on a more detailed analysis of the flight recorder information and examining systems modules and equipment that could influence engine operation. |
Human Factors
Were both pilots seated properly, restrained correctly? A/P to that height seems unusual, was this addressed? B/A SOP? To now, there isn't enough incontrovertible evidence from FDR, CVR to help the cockpit data along very far. 108 knots can't have been acquired with a functional A/P. Nor could it have been allowed by hand, absent ongoing low thrust. The A/P would not have allowed a Stall; Belly on beats nose in, yeh?. Stall is not a result any pilot would choose purposely, choosing it over belly in. Was the AOA (high) a result of the temporary power surge? Any noise heard on the ground that was unusual? Pop. scraping of metal, changing noise levels?
(Prior to "Landing"). |
Quote:-
unless there was a problem with both gearboxes the speed of rotation of the input shaft to the pump is fixed to the speed of N2(3?) and therefore known. Today 22:34 Thanks. A question - how is the speed controlled ? |
Stall is not a result any pilot would choose purposely, The speculation here is bordering on surreal. |
Phil,
The speed is controlled by the fuel going to the burners, N1 in my book, this is determined by the demands of the throttles set by the crew. This is basic gas turbine operation. |
Phil,
The speed is controlled by the fuel going to the burners, N1 in my book, this is determined by the demands of the throttles set by the crew. This is basic gas turbine operation. |
Post missing in previous BA38 thread . . . .
With reference to thread "AAIB BA38 B777 Initial Report Update 23 January 2008" (now closed):
Post #445, which i wrote, described first hand experience with fuel shutoff valves, the equivalent to the T7 spar valves, which closed uncommanded (no B777 or any Boeing aircraft were involved) during flight which resulted in mishaps. There were several replies in reaction to my initial post #445 to which i subsequently replied. I Replied to ChristiaanJ (and Chris Scott) but my reply, which dealt with testing and certification related to EMI/HIRF has been removed from that thread . . . . . In response to the now missing reply the following persons responded of which i show abridged versions below: "Post 451: CONF iture : I'm still on the fuel but Green-dot is producing an interesting reading ..." And: "Post 452: yamaha : I can't keep quiet any longer. Put EMI to bed. Its nothing more than trying to inject a conspiracy theory into the whole tragic affair. It reminds me of all the A320 scaremongering 20 years ago. Lightning will bring it down, power cables will bring it down, the computers will be hijacked by virus's.....all humbug. How many aircraft fly each day and how much EMI is out there 24/7. Please get real." To keep the record straight there is now a mis-representation of the actual amount of posts in above mentioned thread. It makes me wonder what caused my reply to be removed. To "Yamaha" i would like to say that the word "conspracy" will never be part of my vocabulary, neither will scaremongering. I have 34 years of experience working on aircraft and their systems and that experience is based on facts! With the AAIB Bulletin S1/2008 released yesterday, several issues are no longer a matter of concern. Many other issues are still on the table. EMI/HIRF is perhaps one of those issues. I will wait for the final report with great interest. Regards, Green-dot |
Fuel Pump Temps & Pressures
Pumps made by Argo-Tech
excerpts from FAA TYPE CERT. DATA SHEET E00050EN (covers RR Trent 895-17): NOTE 3. MAXIMUM PERMISSIBLE TEMPERATURES FUEL At outlet from HP fuel pump xxUnrestricted xxxxxxxxxxxxxxxxxxxxxxx140C xxMax. during transient overshoots on xxreducing rpm (15 min. limit) xxxxxxxxx165C NOTE 4. FUEL AND OIL PRESSURE LIMITS FUEL MINIMUM FUEL PRESSURE Between sea level and 45,000 feet, not less than 5 psig plus true fuel vapor pressure, measured at inlet to engine LP fuel pump. Maximum pressure at the engine inlet (measured at inlet of LP fuel pump) xxContinuous xxxxxxxxxxxxxxxxxxxxxx60 psig xxTransient xxxxxxxxxxxxxxxxxxxxxxx70 psig xxStatic xxxxxxxxxxxxxxxxxxxxxxxxx170 psig -=MachacA=- |
Originally Posted by airfoilmod
(Post 3923641)
Were both pilots seated properly, restrained correctly? A/P to that height seems unusual
Originally Posted by airfoilmod
(Post 3923641)
To now, there isn't enough incontrovertible evidence from FDR, CVR to help the cockpit data along very far. 108 knots can't have been acquired with a functional A/P.
Originally Posted by airfoilmod
(Post 3923641)
Nor could it have been allowed by hand, absent ongoing low thrust. The A/P would not have allowed a Stall
Originally Posted by airfoilmod
(Post 3923641)
Belly on beats nose in, yeh?. Stall is not a result any pilot would choose purposely, choosing it over belly in. Was the AOA (high) a result of the temporary power surge?
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Machaca
Now you are posting specifications for an engine LP Low Pressure whereas most of us believe that the only pumps on the engine are the high pressure gear type pumps. We would much appreciate knowing the specs for individual High Pressure pumps particularly max output prerssure versus flow rate and minimum inlet pressure to avoid cavitation. You may be able to throw in the minimum measure of lubricity in fuel for continuous operation and how is it measured. When we operators talk about LP Low Pressure pumps we mean tank booster or transfer pumps. |
Short legs
The first officer took control for the landing at a height of approximately 780 ft, in accordance with the briefed procedure, and shortly afterwards the autothrottles commanded an increase in thrust from both engines A little late for a handover of control don't you think? Is it SOP within BA for copilots to fly such short legs? |
The report states,
The recorded data indicates that there were no anomalies in the major aircraft systems. The autopilot and the autothrottle systems behaved correctly and the engine control systems were providing the correct commands prior to, during, and after, the reduction in thrust. Explain to me how a software or EMI or EEC problem could cause this accident and nothing bad shows up in the thousands of recorded parameters.:confused: |
MU3001A
BA SOP is for the P1 for the sector (Captain or FO) to hand over control before TOD to the P2. The P2 then flies the aircraft until the P1 becomes visual and takes control, the theory is that at DA the P1 is looking out, sees the runway and takes control for the landing. If operating with the weather above DA this handover of control usually takes place shortly after 1000RA. In this case it appears that the First Officer was the P1 for the sector and the timing of the handover was not unusual, PEK-130 miles before LHR is quite a long leg. |
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