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BA038 (B777) Thread

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BA038 (B777) Thread

Old 10th May 2008, 16:39
  #1041 (permalink)  
airfoilmod
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Experience

Regarding BA038 and to a greater extent, other investigations, it's important to note that there are as many perspectives as there are stakeholders in the "outcome". Perhaps closest to the pure neutral position is AAIB, as folks back away from their point of view, parochial vestings start to appear. I think that is why those who annoyingly post "Wait for the Report, etc." have an inarguable point. Long ago, when media was more limited, had fewer outlets and showed a small amount of judgment, the public was less interested, simply because information and venue were so limited. A friend died at DFW in the Delta 1011 windshear crash, another lost #2 (727) on takeoff, still another landed with left main gear collapsed. Incidents inform as well as titillate, and that should be the goal of AAIB BA038. I don't take this thread too seriously (with certain few exceptions), but the expanse of the web permits, no, encourages amateurish opinion and rant. Having been involved in many investigations, (albeit working for folks with a huge stake in the outcome), I can safely say in my opinion AAIB at this stage is well ahead of anyone here, it is the nature of the exercise. Rant off, but armed.
 
Old 10th May 2008, 20:41
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Parliamentary Reply

I found this in the House of Lords Hansard - Written Answers - 8 May

Lord Bassam of Brighton:
The Air Accidents Investigation Branch (AAIB) investigation has identified that when the aircraft was at a height of approximately 700 feet, an increase power demand was received at both engine control units. Despite the correct operation of all engine control functions and sufficient fuel on board the aircraft, the engines did not respond.
The focus of the investigation continues to be the fuel system both in the aircraft and on the engines. Under the direction of the AAIB, extensive and challenging full engine testing continues at Rolls-Royce, Derby and some equally, if not more so, challenging fuel system testing is ongoing at Boeing, Seattle, USA.
These tests are collectively aimed at understanding and, if possible, replicating the system/engine performance experienced during the accident.
Fuel experts and statisticians are also involved in the investigation, reviewing and analysing many thousands of data points recorded on the Boeing 777 fleet of aircraft to see if any trends of statistical significance can further contribute to an understanding of the accident.
The Federal Aviation Administration, the European Aviation Safety Agency and the Civil Aviation Authority are being kept fully briefed on the progress of the investigation.
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Old 11th May 2008, 05:11
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Originally Posted by airfoilmod
Regarding BA038 and to a greater extent, other investigations, it's important to note that there are as many perspectives as there are stakeholders in the "outcome". Perhaps closest to the pure neutral position is AAIB, as folks back away from their point of view, parochial vestings start to appear. I think that is why those who annoyingly post "Wait for the Report, etc." have an inarguable point. Long ago, when media was more limited, had fewer outlets and showed a small amount of judgment, the public was less interested, simply because information and venue were so limited. A friend died at DFW in the Delta 1011 windshear crash, another lost #2 (727) on takeoff, still another landed with left main gear collapsed. Incidents inform as well as titillate, and that should be the goal of AAIB BA038. I don't take this thread too seriously (with certain few exceptions), but the expanse of the web permits, no, encourages amateurish opinion and rant. Having been involved in many investigations, (albeit working for folks with a huge stake in the outcome), I can safely say in my opinion AAIB at this stage is well ahead of anyone here, it is the nature of the exercise. Rant off, but armed.
I entirely agree. The other difference between this thread (and other similar ones) vs the AAIB investigation is that they (naturally) have access to a lot more facts regarding the incident than we do. This thread has expounded on many theories. They range from theories which are nearly or totally fact deficient, to those theories which at least try to fit the known facts into their scenarios. Unfortunately, we don't have enough facts to sharpen the focus much more than it has been to this point. We don't have all of the facts we need to entirely exclude some scenarios either. It does help that there are many here who have important insight on the systems involved. It seems to me that the theories identifying the fuel/fuel system versus environmental conditions are the most likely. The post from alex990088 seems to be acknowledgement that this is the case.

In the end, the facts will determine. In the meantime, it is a worthwhile mental exercise trying to put the pieces together. Even though we know that the jigsaw puzzle is missing a number of important bits.
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Old 11th May 2008, 05:51
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Cool More mis-information

Lord Bassam of Brighton:

The Air Accidents Investigation Branch (AAIB) investigation has identified that when the aircraft was at a height of approximately 700 feet, an increase power demand was received at both engine control units. Despite the correct operation of all engine control functions and sufficient fuel on board the aircraft, the engines did not respond.
AAIB Special Bulletin: 1/2008
The engines initially responded
but, at a height of about 720 ft, the thrust of the right engine
reduced. Some seven seconds later, the thrust reduced on
the left engine to a similar level.
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Old 12th May 2008, 15:22
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AAIB Special Report S-3 Issued May 12

Note the issuance of Special Report S-3 by the AAIB on 12 May.
http://www.aaib.dft.gov.uk/latest_ne...in_s3_2008.cfm
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Old 12th May 2008, 16:49
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This should answer a few of the theories postulated on this thread.

http://www.flightglobal.com/articles...-crash-la.html

The possiblities for the incident are being narrowed.
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Old 12th May 2008, 20:01
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I note the report needs a little editing.

It contains the words :-

"...... The autothrottles commanded an increase in thrust from both engines and the engines initially responded. However, at a height of about 720 ft the thrust of the right engine reduced to approximately 1.03 EPR (engine pressure ratio): some seven seconds later the thrust of the left engine reduced to approximately 1.02 EPR. The reduction in thrust on both engines was the result of a reduced fuel flow and all engine parameters after the thrust reduction were consistent with this. ....."

and

"...... and the engines, in order to understand why neither engine responded to the demand increase in power when all of the engine control functions operated normally. ....."

---------

But seriously, I am amazed that the reduced thrust was so similar 1.03 v. 1.02 EPR !
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Old 12th May 2008, 20:05
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New Special Bulletin.

Today the AAIB issued a new Special Bulletin, updating information of previous reports.

Of note:

- No evidence of:
. EMI
. Core Engine Icing
. Bird Strike
. Wake Vortex
. Fuel Contamination

- Actual EPR values: Left 1.03 EPR, Right 1.02 EPR.

- Reduced Fuel flow was detected (could be previously inferred, since the previous report stated that the EEC "reacted" to reduced fuel flow)

- Flow stayed low after FMV was fully open (refuting "low-energy fuel" and "foaming fuel" theories)

- Spar valves operated correctly (previously only stated that they had not been operated by the crew, before the accident)

- The cavitation damage on the high-pressure pumps was fresh (I consider this the most interesting new information)

- No recommendations by either AAIB, Boeing or RR.


Findings so far

- Cause of low engine thrust: low fuel flow

- Cause of low fuel flow: Not the faintest clue.


The upshot: complex test rigs are used at Boeing and Rolls-Royce to recreate the conditions of the flight and hopefully stumble upon something useful.

Data recordings of this and other flights are being examined statistically in the hope of finding unusual parameter combinations, since all parameters by themselves appear to be well within the operating envelope of the aircraft.


Bernd
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Old 12th May 2008, 20:05
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After S3/2008....

Evironmental factors.... fuel flow restriction.... but 'operated within flight envelope'....

as a SLF, I find it puzzling that no SB or general warning to 777 operating companies is deemed necessary: perhaps nature itself will replicate all contributing factors before the AAIB, RR or Boeing manage to do so.

taking account of public interest is a good thing for a public body (that is reading PPrune quite thouroughly and dismissing many theories), but this bulletin is rather worrying: no precautionary measures whatsoever - not very reassuring for a frequentt flyer, neither for some 777 crew I suppose.
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Old 12th May 2008, 20:10
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Borghha, what would the AAIB recommend? Since the cause is not known yet (and this cause is a real mystery resulting in a difficult investigation), how would you suggest avoiding a repeat?
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Old 12th May 2008, 20:22
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well Flight Safety,

how would you suggest avoiding a repeat?
the fact that the environmental factors are mentioned, allbeit without implying a direct causal link, but it being made very clear that there were no mechanical/electrical/electronic failures, nor RFI etc suggests to me that they suspect a link between the prolonged cold soak and the incident. So wouldn t it be advisable to avoid these extremely low OAT s, as long as the real cause is not known?
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Old 12th May 2008, 20:30
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No Evidence

Originally Posted by borghha
[...] made very clear that there were no mechanical/electrical/electronic failures, nor RFI etc suggests to me that they suspect a link between the prolonged cold soak and the incident.
As usual, the AAIB chose the words very carefully. The report says there was no evidence of EMI, core icing, electronics or systems malfunctioning.

But since no evidence whatsoever of what went wrong has been found, it may have been one of those things, just without leaving any evidence that could be discovered with the methods employed so far.


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Old 12th May 2008, 20:39
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Narrowing it down to low fuel pressure and low flow from the tanks and fresh cavitation to the hp fuel pumps and the isa temp at altitude was -20 that day causing other flights on that route to descend to FL250 that day continues to point to super cold fuel causing fuel waxing to not let the engines come up to commanded power. How often do they check the 777 fuel sensor circuit for accuracy once it is installed? Obviously their low fuel temp light didn't come on in cruise but why did the others?
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Old 12th May 2008, 20:40
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What I hope the AAIB doesn't eventually issue is a "probable cause" result for this accident, meaning "we don't know what caused it, but we think it was this".
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Old 12th May 2008, 20:46
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Bubbers44, it's easy enough to test temp probe accuracy in the current configuration. Just instrument the fuel tank at multiple locations and go fly it at cold levels.
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Old 12th May 2008, 21:00
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Phraseology

I note with interest the phrasing of the AAIB update:

Begins:

Under the direction of the AAIB, extensive full scale engine testing has been conducted at Rolls-Royce, Derby, and fuel system testing is ongoing at Boeing, Seattle.

Ends.

So, to me that suggests that whatever has been done at Derby now is complete, and that the work at Seattle is continuing.

I can imagine that had the work at Derby shown there to be an issue with the engines' fuel systems, then that would have been reflected in today's AAIB update. But... apparently not. So, it looks as if summats up with the aircraft's fuel system, for whatever reason.
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Old 12th May 2008, 21:01
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Mr. Gollin

The more similar the results at each engine of a fault in ETOPS the deeper the threat to the concept. By this I mean such "identical" EPR's suggest a "single" fault. Moving in reverse, the further back upstream the fault, the more troubling the implication if it can be shown that it caused simultaneous fuel starvation. Conversely, the more individual the result, the safer the format is from criticism. My first reaction to the report of the short landing was, it's Etops, engine failure is nearly impossible, and dual engine failure is out of the question. Simultaneous dual engine failure? The language in this last report also mentions no "excessive" water in the fuel. That isn't exactly encouraging.

Bsieker- The theory about cavitation being "fresh" was offered by the Boeing Safety Pilot (3-14-08): "not long before the incident". Though it is "fresh" as related to AAIB findings.

borgha- I agree the lack of any useful remedial suggestions is troubling.
 
Old 12th May 2008, 21:10
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Yes it would be possible to do that for certification but very expensive to do that for recurring checks once certified. No one is going to spend thousands of dollars to have maintenance go to max altitude to check one light to see if it comes on at an extreme temp especially if you have to cold soak for hours in the right conditions to make it happen. Most polar flights the light doesn't come on. On this day several flights had it happen and descended to FL250 to get it out. If they had a ground check to calibrate I would be interested in how they would do it, sensor being in the fuel tank submerged with fuel and all. It seems they could check it easily now since they could just cut into the tank and test it in a controlled temperature box and see if it was accurate.
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Old 12th May 2008, 21:32
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Apart from the suspiciously similar EPR of the two engines (1.02 and 1.03) there is an interesting line in the report :-

"....... The evidence to date indicates that both engines had low fuel pressure at the inlet to the HP pump. Restrictions in the fuel system between the aircraft fuel tanks and each of the engine HP pumps, resulting in reduced fuel flows is suspected. ....."

I find it almost incredible that two different systems could suffer almost exactly the same restrictions HAVING INITIALLY RESPONDED, but I await the reasons with great interest.
.
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Old 12th May 2008, 21:32
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I can imagine that had the work at Derby shown there to be an issue with the engines' fuel systems, then that would have been reflected in today's AAIB update. But... apparently not. So, it looks as if summats up with the aircraft's fuel system, for whatever reason.
What - maybe something like:
Restrictions in the fuel system between the aircraft fuel tanks and each of the engine HP pumps, resulting in reduced fuel flows, is suspected.


NoD
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