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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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