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AAIB BA38 B777 Initial Report Update 23 January 2008

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AAIB BA38 B777 Initial Report Update 23 January 2008

Old 5th Feb 2008, 11:02
  #281 (permalink)  

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So, tell us Mouse...where does all this inside info come from?

Are you part of the investigation team, a crew member, a BA flight dept pilot, or are you having us on?
Look at any of my posts, as far as I am aware I have never posted anything that was not factually correct. No I am not having you on nor do I feel a need to pretend to know more than I do.

We dont KNOW exactly when and if FUEL LOW drills were performed.
With respect I think it is being overlooked that from the first recognition of a problem to actually hitting the ground was circa 45 secs. The luxury of careful analysis and a decision on which checklist to carry out was not available and also bear in mind that very few B777 checklists are memory drills and that 'Fuel Low Qty' is not one of them.

It will become apparent that the flight crew did what would seem like a good idea at the time. We will have the comfort of our armchairs to decide what they should or should not have done. On the evidence so far I have no criticism and a sense of relief that my abilities were not the ones that were tested that day nor subject to detailed scrutiny, officially and unofficially, in the days past nor weeks to come.

Failure of one Xfeed to open suggests it was either done very late , after engine "rundowns" and not not fully performed by the system,
...OR , it was selected before , and,(with one Xfeed failed at CLOSED) actually contributed to the "rundowns".
...Or ,is it possible that in fact one Xfeed was failed OPEN throughout the flight?(then what?)
Just for clarity the 'Fuel Low Qty' checklist on the BA B777s calls for EITHER crossfeed valve to be opened not both. Therefore, the assumption that one crossfeed valve had failed either at the time or previously is incorrect.

Neither had a crossfeed valve failed open throughout the flight.

Last edited by M.Mouse; 5th Feb 2008 at 11:14.
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Old 5th Feb 2008, 13:36
  #282 (permalink)  
 
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FUEL QTY LOW 777 flight manual

CROSSFEED SWITCH (Either) ON
(Ensures fuel is available to both engines if the low tank empties)
FUEL PUMP SWITCHS (AII) ON
(Ensures all fuel available for use)
Plan to land at nearest suitable airport
GROUND PROXIMITY FLAP OVERRIDE SWITCH OVRD
Use flaps 20 and VREF 20 for landing
(Increased speed at flaps 20 provides improved elevator control for landing flare in the event of a dual engine flameout)
Avoid high nose up attitude and excessive acceleration or deceleration
(prevents forward pumps from uncovering)
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Old 5th Feb 2008, 18:39
  #283 (permalink)  
 
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Would be interested to know if it took more than 45 seconds to look that lot up :-)
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Old 5th Feb 2008, 19:00
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It's great to witness a much more balanced, calm and knowledgeable discussion of these matters here than was the case a short while ago...

With this seeming more like a one in a million 'act of God' occurrence, whatever it might have been, we can only give thanks that the outcome was so benign and that hopefully it will provide pointers to making air-travel even safer in the future...
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Old 5th Feb 2008, 19:37
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Suction feed

Ref post 275

" The burners sucking fuel without pumping" ...... Fuel is injected into the combustion chamber of any jet engine, in the form of a very fine spray, so it will ignite easily and combust as completely as technically possible. Such a fine spray can only be achieved with fuel under very high pressure so you definitely need a high pressure fuel pump (which is mechanically driven by the high pressure rotor, N2 or N3).
Any pump that delivers pressure on one side, will suck on the other side. Normally, an aircraft manufacturer will make the plumbing of fuel pipes of such dimensions, that in principle, the suction of the high pressure pump, possibly assisted by gravity, will be enough to get fuel from the tanks to the engines. However, simply "enough" is never sufficient in aviation, so every tank will have a redundant number of low pressure supply pumps in the plumbing system to guarantee ample delivery of bubble free fuel to the inlet of the high pressure pump under all conceivable conditions. Those supply pumps are normally electrically driven, and their electrical power source of course is never just the same source for all pumps.

I hope that post 275 is thus clarified for interested readers.
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Old 5th Feb 2008, 21:19
  #286 (permalink)  
 
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Fuel transfer begins when EITHER main tank is below 13,100Kgs.
Thanks, M.Mouse...
So scavenging would probably begin 3 1/2 hours after the Center Tanks pumps had been switched off. Add another 2 and a bit hours to this to get almost 6 hours. So 2 or more hours before arrival, the fuel level in the Center tank should be zero.

Rgds.
NSEU
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Old 5th Feb 2008, 22:49
  #287 (permalink)  

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From my numbers G-YMMM held 29,100kgs of fuel in each wing tank when full (usable, level attitude and using a density of 0.8029 kgs per litre).

Therefore once the centre wing tank pumps had been selected off 16,000kgs of fuel would need to be used before scavenge transfer started. Using an average fuel burn per engine of say 3,000kgs per hour that is roughly 5 hours of flight.

I cannot recall ever monitoring the scavenge transfer that closely but although I do not doubt the MINIMUM transfer rate of 200kgs per hour quoted earlier I think the normal rate is a good deal greater. For example at 200kgs per hour just 800kgs in the centre tank would take 4 hrs to transfer. I may well be wrong and will endeavour to time the transfer when next I have the opportunity but I am puzzled where this somewhat esoteric discussion is leading!
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Old 5th Feb 2008, 23:34
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For example at 200kgs per hour just 800kgs in the centre tank would take 4 hrs to transfer.
As SwedishSteve said earlier, there are two scavenge pumps, so the minimum rate would be closer to 2 hours.

but I am puzzled where this somewhat esoteric discussion is leading!
I was thinking about contaminants/water in the CWT. If my manuals are correct, there has to be a huge amount of water in the CWT before a warning is raised on the flight deck.
As the dregs were being sucked from the centre tank, I was wondering at what time this process would be completed. Of course, the contaminants have to find their way down from the outlets of the scavenge pumps to the bottom of the wing tanks where the wing tank pump inlets are. I don't know how long this would take.
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Old 6th Feb 2008, 07:48
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HEre is some more info on the fuel system. Note the last paragraph

http://online.wsj.com/article/SB1201...googlenews_wsj


Pilots and safety experts said both engines of the British Airways plane normally would have been draining fuel directly out of the same center tank during final descent to the field. Jetliners rely on additives to prevent ice formation inside tanks and fuel lines, but they don't typically have heaters to warm fuel. In the past few days, investigators have found internal damage to at least one fuel pump suggesting that the pumps weren't receiving adequate fuel flows, according to one person familiar with the details.
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Old 6th Feb 2008, 09:55
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As SwedishSteve said earlier, there are two scavenge pumps, so the minimum rate would be closer to 2 hours.
My mistake I misread that. His quote from the AMM says that the scavenge rate is 200kgs per hour not per pump. However, his rough calculations indicate he reads that as 200 kgs per hour per pump. It would make more sense and fit in with my impression of the length of time it takes for the CWT to be emptied. As I said previously I will time it at the next opportunity!
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Old 6th Feb 2008, 11:44
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Hallo boys and girls

Look what I found:

http://meriweather.com/777/over-777.html

Please, don't tutch anything. It may be connected to a real
trippel seven!
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Old 6th Feb 2008, 12:14
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Pilots and safety experts said both engines of the British Airways plane normally would have been draining fuel directly out of the same center tank during final descent to the field. Jetliners rely on additives to prevent ice formation inside tanks and fuel lines, but they don't typically have heaters to warm fuel. In the past few days, investigators have found internal damage to at least one fuel pump suggesting that the pumps weren't receiving adequate fuel flows, according to one person familiar with the details.
I certainly hope these 'experts' aren't involved in the real investigation!
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Old 6th Feb 2008, 12:46
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I certainly hope these 'experts' aren't involved in the real investigation!
Why
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Old 6th Feb 2008, 12:50
  #294 (permalink)  
 
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As the dregs were being sucked from the centre tank, I was wondering at what time this process would be completed. Of course, the contaminants have to find their way down from the outlets of the scavenge pumps to the bottom of the wing tanks where the wing tank pump inlets are

Yes there are two transfer jet pumps. One on each side. But there are water scavenge jet pumps as well in all three tanks. These operate all the time and scavenge water from all the odd cavities it may lodge and direct it to the booster pump inlets.
So when you get down to the dregs of the centre tank, it will not be a chunk of water, if the water scavenge jet pumps were working. In my last incarnation as a Tristar engineer, we used to regularly go in the tanks to clean the jet pumps. the jet used to get blocked by debris, usually thiokol from the tank sealing. There is no indication that these pumps are not working.
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Old 6th Feb 2008, 14:06
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I certainly hope these 'experts' aren't involved in the real investigation!

Why
Because the fuel isn't being used from the Centre Tank.. because there wouldn't be any in the Centre Tank during the descent... and...
jetliners do have fuel heaters. They use heat exchangers on the engines (using hot oil to warm cold fuel). To a lesser extent, there are also heat exchangers in one of the wing tanks to cool hydraulic fluid.

Even if the damage to the pumps was prior to the crash, all 4 pumps would have to be damaged to cause both engines to not respond... and the gravity feeds would have to be blocked, too.

From where are they getting these so-called experts???
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Old 6th Feb 2008, 17:01
  #296 (permalink)  
 
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Descent fuel tanks

My experiance is with 737's but I can't imagine this is different on the 777. Fuel is normally used first from the center tank so descents would normally be using wing tank fuel. This is because weight in the wings is more easily supported from a structural point of view (this is why there is a concept of maximum zero fuel weight on transport aircraft). In the 737, the center tank fuel pumps operate at a slightly higher pressure so that the center tank will empty first even if all tanks are online.
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Old 6th Feb 2008, 17:02
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Is it just me.....

A 777 of which there are many hundreds flying around (over the pole, over London etc) loses power on both engines on short finals and crashes and almost no information advice etc from any source... Boeing, CAA, FAA, AAIB. Not so much as a, just in case, check the wing nut on the outer flange on the right wing thingymbob.

The FDRs are so sophisitcated these days they can tell how many times you scratched your a*s during the flight (thousands of parameters monitored) but, after three weeks, almost nothing............ but BA seemed to know enough to parade the pilots
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Old 6th Feb 2008, 17:18
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A sophisticated FDR can tell you a lot about what happened and when. But it can't necessarily tell you WHY, and if you don't know that you can't tell people to check for a cause.
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Old 6th Feb 2008, 22:27
  #299 (permalink)  
 
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The fuel temperature at the outlet of the fuel cooled oil cooler would be lowest at the moment the crew/AT increased the thrust at 600'. This is when the engines lost thrust.

I've spent far too much time thinking about this and my conclusion is that a prolonged cold soak followed by a long low/idle thrust descent cooled the whole system (engine oil and fuel) such that when thrust was requested the increase in fuel flow through the fcoc resulted in the fuel temperature and therefore viscosity being low enough to disrupt the proper flow through the fuel metering unit or other downstream fuel components such that the requested fuel did not reach the fuel injectors.

If I'm right do i win a prize?
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Old 7th Feb 2008, 01:57
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"It is a capital mistake to theorise before one has data. Insensibly, one begins to twist facts to suit theories, instead of theories to suit facts"

Observation by Sherlock Holmes in Arthur Conan Doyle novel. Still so true today.............

Last edited by 777fly; 7th Feb 2008 at 01:58. Reason: spelling
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