Snanceki
 

Or the unlubricated and uninspected stripped Jack screw in the Alaskan MD80 elevator. Like the man said, Human Endeavor, weak link, etc. As an engineer, you focus on How? The Public wants Why? Why is about fate and gross mistakes and should be elsewhere. Where is Cranfield? And as has been pointed out, the Fuel Temp. sender is in the Port (warm) wing.

In response to najavens
 

Quoting najavens:

1. Identifying the parts:
The parts most suspect IMHO, are of electro-mechanical composition and the mechanical part(s) of this hybrid design are the first components one finds in the engine fuel feed system, upstream from the engines toward the fuel tanks, the spar valves. They only have 2 positions: open or closed. These mechanical parts in the engine fuel feed lines are nothing but slaves to what the electrical parts, the control relays, of this "symbiosis" instruct them to do.

The electrical parts of this hybrid design are buried deep inside the aircraft's hull, nowhere near their mechanical "slaves." If for whatever reason these electrical parts were to be disrupted in their normal functioning and moved their mechanically slaved "other half" from open to closed position, starvation of fuel to both engines would be guaranteed.

Just a theory until proven by facts of course but if they were affected, i won't dare speculate as to what the source of the disruption could have been. Maintenance issues? Items carried on board, alien to the aircraft's systems? Were such items located in the passenger cabin or perhaps in a cargo hold? The list of possibilities could be long . . . . . and the possible causal source a needle in a hay-stack.

2. Mechanical back-up:
With reference to mechanical systems as a back-up in the fuel system, i would not be so sure about that. See my first comment above, "identifying the parts."

3. Both engines:
Too much emphasis is put on RF affecting both engines, this has already been discounted by the AAIB report which confirmed FCUs and EECs functioned as advertised. What ever the source of the disruption, if it could have potentially affected parts of the left and right engine fuel feed systems, especially when in close proximity to eachother in a confined space, the electrical parts mentioned in my first comment above would be very likely candidates in the chain of events resulting in the generally perceived theory of a common source failure (they meet close proximity and confined space criteria, making them perhaps vulnerable to a single, yet to be defined, causal source).

Green-dot

Re: Sunfish, Airfoilmod and irritation
 

Good posts. Aviation safety development is based on openness and frankness. While adhering to that leads to extraneous "naive worthless contributions" and other extra "noise", my feeling is that that is still preferable to suppression of possibly valuable contributions, for whatever reason. In other words, moderation could preferably be limited to obvious repetitions and totally clueless contributions. But contributions by people from a different field should IMHO be treated with some respect. There just might be nuggets in them. :ok:

Just my $0.02.

Water in fuel
 

Sunfish - have you seen the post by UNCTUOUS (P35 post681) where in response to several reports from users, Boeing theorise that water might be accumulating in the centre tanks of -200LR and -300ER aircraft?

Whilst the system for dealing with water is different in the -200ER, that doesn't mean that water can't get into the -200ER tank.

Timing
 

And the timing fits. Scavenge from centre tank to wing tanks starts when 29,000 pounds of fuel (total) remaining - i.e. roughly within half an hour of landing on the grass at LHR. (see post 572).

Wait for the report.

Cargo/Container Restraint.

Does anyone know the design horizontal g restraint on baggage and freight containers for the B-777?

The peak decelleration may have come close to max. Did any break loose?

No.

(my emphasis.)

So not 29,000 total, but 29,000 in either wing tank. Wing tank capacity is 64,100 pounds, each.


Bernd

Post incident I know religiously check the Maint Page Fuel QTY pages for evidence of water in the tanks.
About a month ago it showed water centre tank on a GE 200ER, called up Maintrol and they had to come out to check it (ai drip stick the centre tank).
No water apparent in the sample though.

What if no proof of cause - what does AAIB do?
 

Warning: I'm non-professional; not crew, not engineer - just guest and thanks.

I've been wondering what would the AAIB do if they could not demonstrate to a high probability the cause of the accident.

If, for example, the AAIB were convinced, but could not prove, that the fuel quality had been lowered by cold-soaking for an extended period of time and that this had lead, in some unknown way, to the accident, what would they do?

Presumably the AAIB would operate on the precautionary principle.

Might they:
1) Recommend/demand/regulate the avoidance of extended flight-time in very cold air masses;
2) Demand that if aircraft had experienced extended flight-time in very cold air masses then they must loiter for some time in warmer air before descending for landing?

If the AAIB was thinking of 1 or 2 then, I assume, they would have to convince, and then act in unison with, equivalent international agencies - that would take a lot of time and effort. And just imagine how all the other interested parties would react.

Of course, in this scenario the AAIB have until the coming northern hemisphere winter to sort this out.

Has such a situation (i.e. no proof but suspicion of likely cause) arisen before and how did the industry react?

Regards, Tanimbar

grasping at a different straw
 

It is suggested that Ba038 was given an unusually long soak at -75degrees.(Around ISA -20 ....more unusual in that it is also suggested that most aircraft on this route took precautions and reduced altitude)
...How many hours would this have been? and did it continue to top of descent? Would all engine internal temperatures be running as much as 20 degrees lower than at the same altitude with a normal OAT of ISA.?
Did it at any time in a long Flight-Idle descent pass through an area of high humidity and low temp (cloud)?
.....We do know that a long taxi at Idle in fog can produce "core-icing", in spite of having engine deicing switched on, which has to be countered by a clearing procedure Thus allowing continued operation without damage occurring.
....Does mild core icing ever occur in flight?preventing acceleration?
....Could an amount of core ice accumulate ,and not be readily shed, on such a descent commencing with a core temp already 20 degrees lower than usual? with normal engine deicing operating at less than 100%?


NOT very likely.If it had happened thus, there would probably be data records,or signs of internal damage. Or the engines would not have run down again after they had succeded in initial acceleration.
...I still think its fuel,plus a bit of wind shear.

Think TWA800...you should know the rest.

and the AAIB/NTSB can't demand or regulate, their job is to investigate and recommend. An no they won't wait for the winter months. As soon as they learn anything that can/should be fixed, even if not in the causal chain they will issue a recommendation for the industry to act on.

bsieker, thanks for your correction on when fuel scavenge starts. With the correction: 13,500kg+13,500kg+900kg of fuel (total) remaining when scavenge started; 10,500kg remaining on approach to LHR (AAIB); difference 17,400kg; fuel being used at a rate of maybe 5,700kg/hr; so fuel scavenge would have started about 3 hours before it hit the grass, i.e. in cruise. Would scavenge have finished, though?

Spar valve solenoids.
 

Green-dot.
Solenoids are sometimes activated by stray electromagnetic fields
as you suggest. A Shorts 3-30 fell on its "knees" when an errant field
pulled the gear pins, while pax were unloading. Perhaps it happened more
often.

Yes.

The figures look reasonable; at the minimum fuel scavenge rate of 400kg/h, it would take 2 hours, 15 minutes to scavenge all of the 900kg from the center tank. It would have finished some 45 minutes before the end of the flight.

Likely before TOD, but I cannot know for certain.


Bernd

alright then - switching horses, are the light patches on the underside of the wing behind the engines in this photo unusual or not?

http://forum.skyscraperpage.com/show...3&postcount=47

it's a long time since I stood at the end of a runway in winter...

(sorry if this point has already been settled)

bsieker:
Assuming the scavenge system was working properly, and not iced up.

If scavenge failed then the fuel sensors did too, as the AAIB state that the fuel was (indicated to be) in the wing tanks on approach.

To jake brake:

Inadvertent in-flight liftdumper deployment on a Fokker 100 comes to mind from several years ago. The cause was determined to be the combination of EMI from a faulty Flight Control Computer on a wheel speed signal, a skid control box power-up spike on landing gear DOWN selection, and liftdumper arming before landing gear extension.

Ref. sources below:

http://www.federalregistersearch.com...3062-filed.asp

http://www.federalregistersearch.com...9512-filed.asp


Green-dot

Not necessarily...
 

The subject of the observation was the timing rather than the failure of fuel scavenge. Ice could possibly delay the onset of scavenge until some time during the descent, then melt away and be scavenged as water.

and:
Quote from Boeing relating to 777-300ER (not exactly the same scavenge arrangement, but might or might not have similar lack of instrumentation - any lurking 777 pilots able to comment or confirm?)

(My bold formatting, and my italic clarification)