Plane lands short of runway.

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  • #126
Astronuc
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Curiously enough the tropopause temperature is normally higher in winter time.
Did this flight fly at an unusually high altitude? Or were there other flights above this one? Were there other flights from Beijing that went to other places in Europe, e.g. Scandanavia or Berlin or Paris, which flew similar distances or higher or more northerly, or did this flight hit a perculiarly cold mass of air?
 
  • #127
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Did this flight fly at an unusually high altitude? Or were there other flights above this one?

No, it flew around the most favorite flight levels FL 340 -400. (times 100 feet with standard pressure altitude 29.98 inch or 1013.2 hPa). The tropopause starts somewhere at those levels above which the temperature stabilizes.

Were there other flights from Beijing that went to other places in Europe, e.g. Scandanavia or Berlin or Paris, which flew similar distances or higher or more northerly, or did this flight hit a perculiarly cold mass of air?

Yes it was much colder than normal. And there was one other unusual thing:

During the descent, from Flight level (FL) 400 the aircraft entered the hold at Lamborne at FL110; it remained in the hold for approximately five minutes, during which time it descended to FL90.

Normally ATC manages to avoid holding patterns, the longer period of time it stayed at lower levels helped warming the fuel again.

So how about the next scenario?

Although the fuel in the tanks never reached critical low temperatures, it may have done so in the fuel pipes, causing partial freezing, which damaged both fuel pumps a bit.

The hyper cold fuel (Freds scenario) during the prolongued flight period increased the entraining of air in the fuel, also facilitated by the pressurizaton of the fuel tanks.

The longer period in the approach fase caused the fuel to warm somewhat longer as normal, causing a super saturation condition.

The damaged fuel pumps may have facilitatedhttp://pdf.aiaa.org/preview/CDReadyMASM07_1064/PV2007_337.pdf [Broken], decreasing the fuel flow.
 
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  • #128
FredGarvin
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Ah crud. I always get this backwards. Air solubility increases with an increase in temperature. That kills my theory. CO2 is the gas that solubility increases with a decrease in temp. This is why I don't design fuel systems :tongue2: Although, I think I like Andre's mention of an increased demand on the low side of the pumps. A sufficient demand would cause the low side to go down so much as to match the vapor pressure and cavitation starts.
 
  • #129
Astronuc
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777's power loss concerns aviation officials
http://www.usatoday.com/travel/flights/2008-02-26-777_N.htm

AIAA Daily launch said:
Re: 777's power loss concerns safety officials.
USA Today (2/27, Levin) reports that the recent crash of a Boeing 777 at Heathrow Airport because of power loss "has transfixed the world's aviation safety experts. Not only has the cause so far eluded accident investigators, but the potential impacts are enormous." Bernard Loeb, a former chief investigator for the U.S. National Transportation Safety Board, said, "This is an extremely significant investigation. You cannot have a loss of power in both engines." It is still "too early to indict the 777's safety," experts contend, "but the details of the crash at least raise the possibility that designers overlooked a vulnerability in the engines, the fuel system or the electronics." So far, "one of the few viable clues" investigators have found "is the 'abnormal' wear found on fuel pumps on each engine. The damage indicated the pumps may have run dry." However, investigators "said that finding just raises more questions. How is it possible for fuel flow to be blocked nearly simultaneously in two separate fuel tanks?"
Well, avaiation safety authorities are taking this very seriously.
 
  • #130
FredGarvin
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Well, avaiation safety authorities are taking this very seriously.
I will say that, despite being a government agency, The FAA does take every crash/mishap extremely seriously. They definitely do not screw around.
 
  • #131
Astronuc
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It's worrisome that "'abnormal' wear found on fuel pumps on each engine" indicates that "the pumps may have run dry." On both pumps - simultaneously! Redundancy - two separate tanks and fuel systems, didn't overcome whatever common failure mode is responsible.

So the have to be wondering - can it happen again, and what is the potential to affect all aircraft?
 
  • #132
Moonbear
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It's worrisome that "'abnormal' wear found on fuel pumps on each engine" indicates that "the pumps may have run dry." On both pumps - simultaneously! Redundancy - two separate tanks and fuel systems, didn't overcome whatever common failure mode is responsible.

So the have to be wondering - can it happen again, and what is the potential to affect all aircraft?

Have they considered inspecting the fuel pumps on a similar aircraft to see if this "abnormal wear" is a flaw in the pump design that had been developing for some time until reaching a critical failure, or if it really was something due to unique and immediate circumstances of the fuel delivery just prior to the crash?
 
  • #133
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Have they considered inspecting the fuel pumps on a similar aircraft to see if this "abnormal wear" is a flaw in the pump design that had been developing for some time until reaching a critical failure, or if it really was something due to unique and immediate circumstances of the fuel delivery just prior to the crash?

Be assured that all B-777 fuel pumps are being checked right now. Reaction on this kind of thing is immediately and adequate. Also if they had found any other pump with that damage all unchecked aircraft are grounded automatically. Since that didn't seem to happen, they probably did not find similar problems.

Running completely dry would have caused engine flame outs for sure, that didn't seem to happen but again cavitation with air bubbles is a posibility or perhaps fuel with a too high viscosity due to extreme low temperatures during transport in the fuel pipes.
 
  • #134
Art
And finally a result;

Ice in fuel caused Heathrow 777 crash


Nasty chill provoked reduced fuel flow

The investigation has shown that the fuel flow to both engines was restricted; most probably due to ice within the fuel feed system. The ice is likely to have formed from water that occurred naturally in the fuel whilst the aircraft operated for a long period, with low fuel flows, in an unusually cold environment*; although, G-YMMM was operated within the certified operational envelope at all times.

The AAIB, while describing the incident as "the first known occurrence of this nature in any large modern transport aircraft", stresses: "All aviation fuel contains water which cannot be completely removed, either by sumping or other means. Therefore, if the fuel temperature drops below the freezing point of the water, it will form ice."
http://www.theregister.co.uk/2008/09/04/heathrow_777_verdict/

Full report here http://www.aaib.dft.gov.uk/sites/aaib/cms_resources/G-YMMM Interim Report.pdf
 
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  • #135
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??? There are several jet fuel anti -icing products on the market.
 
  • #136
wolram
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flow to both engines was restricted; most probably due to ice within the fuel feed system.

Most probably? sure that inspires confidence, if i ever fly again i will ask if this aircraft comes with addatives.
 

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