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BA038 (B777) Thread

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BA038 (B777) Thread

Old 18th Feb 2008, 19:44
  #41 (permalink)  
 
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A fuel leak from the British Airways Boeing 777 which crash-landed at Heathrow could have engulfed passengers and crew in a fireball, a report has revealed.
Here was me thinking the Telegraph was a respectable newspaper
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Old 18th Feb 2008, 19:53
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Reading the report, specially this part:
The airspeed reduced as the autopilot attempted to
maintain the ILS glide slope and by 200 ft the airspeed
had reduced to about 108 kt. The autopilot disconnected
at approximately 175 ft, the aircraft descended rapidly
and its landing gear made contact with the ground some
1,000 ft short of the paved runway surface
they owe a lot to keeping the autopilot on (and its design as well)!
That way all possible energy was used up to its full extend, bringing the aircraft within the airport perimeter.
I don't think a human could have done it better, probably not, as a pilot would have unconsciously lowered the nose.
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Old 18th Feb 2008, 19:57
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Cavitation

Can someone explain how 'evidence of Cavitation' in the HP fuel pumps is being considered here?

Is it that the pump is trying to pump from an obstructed source causing bubbles (cavities) in the fuel or that there is evidence that the pumps are physically damaged?

What will be the evidence of cavitation? assuming THIS is a good explanation of such?

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Old 18th Feb 2008, 20:00
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As observed in an earlier post, all aboard were unbelievably lucky that BA038 ran out of lift where it did, landing on the only bit of waterlogged lawn within miles of their approach path.
I am sure that the 2 pros flying that sector were trying to get it onto 27L, which in the circumstances would have likely had a much more injurious outcome.
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Old 18th Feb 2008, 20:01
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http://edition.cnn.com/2008/WORLD/eu...ef=mpstoryview


What was it then if not mechanical?
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Old 18th Feb 2008, 20:04
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Evidence of cavitations would be small pits on the tips of the impeller blades of a certifugal pump, and in other key places of the pump (depending entirely on the design).

The pits are caused by the rapid collapse of bubbles.

Bubbles can be caused not only entrained air (such as a seal leak) but also when the fuel vapourises (ie. 'boils') at partial vacuums.
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Old 18th Feb 2008, 20:10
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The report does not say that cavitation caused the problems, nor does it say when it occurred, It could have occurred at any time from new, up to the time of the crash.
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Old 18th Feb 2008, 20:13
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Cavitation in itself does not cause a problem unless there is failure of the components themselves as a result of it, or unless the effects of cavittion causes a significant degradation of performance.

Cavitation however is a symptom of a choking of flow on the inlet of a pump, or the entrainment of air.

An example of cavitation could be the addition of a lighter solvent in the fuel which vaporises at a lower temperature than the bulk of the fuel. The suction pressure of the pump could cause the vaporisation of the additive and so cause vapourisation. The report does not report fuel contamination so this can be ruled out.

Another example of cavitation is when a restriction which is on the discharge side of the pump is suddenly taken away - the suction flow just cannot keep up, the pressure drops and cavitation occurs.

At this point I still go for: failed seals due to low temperature, then regaining flexibility on loss of altitude, then entraining air and causing foaming.
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Old 18th Feb 2008, 20:28
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Cavitation..????

Mind the following information given in the report:

"The manufacturer assessed both pumps as still being capable
of delivering full fuel flow."



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Old 18th Feb 2008, 20:34
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I sense Trolls in here.

I don't care whether the autopilot was left in deliberately or not, - it worked.

I do however know far too many professional pilots who believe they can do better than the automatics, usually wrongly!
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Old 18th Feb 2008, 20:37
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I wasn't really getting at fuel waxing/freezing in my previous post......I was more thinking along the lines of water Hygroscopicly suspended in the fuel freezing somewhere in the system during the flight.

However all this is pure speculation at this stage.
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Old 18th Feb 2008, 20:38
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At least all that garbage . . . . .

QUOTE: "BoeingMEL wrote: "............ at least all that garbage about EMI can be buried..... as can fuel exhaustion, windshear, finger trouble, Gordon Brown's heavies..."

To be fair, the report doesn't appear to rule any of that out...

Until the investigation is concluded anything is a possibility!" UNQUOTE

Exactly. Nothing can be ruled out at this time. Reading the report the investigators apparently are confronted with evidence of a normal functioning machine, which for a short period of time did not function normally. In other words, perhaps an intermittent failure of some kind, at this time not yet duplicated.

To quote the report: "The recorded data indicates that there were no anomalies in the major aircraft systems."

Question is then, what could have failed that is not recorded?

Regards,
Green-dot

Last edited by Green-dot; 18th Feb 2008 at 21:01.
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Old 18th Feb 2008, 21:00
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Originally Posted by zukini View Post
They have just said "Damage to the fuel pumps caused the crash"

I'm certain I read in the report that the pumps would not stop working in this condition.
You're right - report said they were assessed as: "still being capable of delivering full fuel flow".

I was wrong though - I was sure we were going to hear that the cause was the crew pulling the fire handle & engine cutoffs in the wrong order, with the AAIB issuing a safety recommendation to stop it happening again.

[followed by, for the particularly on-the-ball reporter, a retrospective of Kegworth, which will turn out to be "eerily similar" because of the words "fire handle" "engine" and "boeing"... ]
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Old 18th Feb 2008, 21:07
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i smell trouble ahead and no one rightly is going to stick their neck out and rightly till the final report is issued.
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Old 18th Feb 2008, 21:08
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No Fault Found.

Hmmmm.

The cavitation damage and some FOD in the tanks is not much to go on!!

So there was fuel in the tanks, the metering valve was fully open, and the pump was capable of supplying fuel.

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Old 18th Feb 2008, 21:14
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Cavitation??

Mind the following information given in the report:

"The manufacturer assessed both pumps as still being capable
of delivering full fuel flow."


Yes, that's right, and what is your point exactly? A scuffed wall of a car tyre does not alter its stopping distance. A pump that shows evidence of caviatation does not particularily alter its performance, and would still allow full fuel flow. They are both evidence of what has happened.

HOWEVER, a pump that is undergoing caviation at the time however is severely suffering in performance.

Would I buy a centrifugal pump that had suffered cavitation? Yes, no problem, (within limits) the key is not to drive the pump so that cavitation occurs.
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Old 18th Feb 2008, 21:18
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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.
This would seem to suggest that the correct signals were getting through to both engines and the engines were trying to respond accordingly. Apparently no other as yet significant defects have been found.

Does this therefore narrow down the possible cause to a momentary absence of liquid Jet A1 under pressure at the burners?

I am totally speculating here, but given that air temperatures were lower than Jet A1 freeze temperature, and even though the tank temperature never got to critical levels according to instrumentation, would it be possible for a deposit (perhaps like cardiac plaque in arteries) of wax or frozen fuel to form somewhere in the fuel pipework?

As it warmed such a plaque could let go, blocking a filter and perhaps giving an engine the mechanical equivalent of a heart attack?

Of course that idea stretches credibility because it had to happen to both engines within seven seconds of each other, there was no EICAS message about clogged filters and it may be physically impossible to put a skin of frozen wax on the inside of a pipe thats carrying -34C jet A1.

No more speculation from me till the next official report.
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Old 18th Feb 2008, 21:20
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Re: The Fire Swith does close the Spar Valve!

Originally Posted by bsieker View Post
In the case of BA038 the path from the fire handle to the spar valve was damaged, and although the path from the cutoff lever to the valve was ok, it was isolated by the fire handle, which on this occasion was activated before the cutoff lever.
Perhaps worth noting that this was only the case on one wing, on the other side (as I read the report) both paths to the valve were cut by the damage, so no action would have closed it.
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Old 18th Feb 2008, 21:24
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Sorry if this sounds oversimplified, but if the tanks had enough fuel, the EECs responded correctly to the request for more power, the fuel metering valves were wide open, and the HP fuel pumps were probably cavitating, then it seems reasonably clear to me that something was probably blocking the fuel flow.
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Old 18th Feb 2008, 21:29
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Common mode failure.
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