QUOTE:

I also understand they had had an continuous(ish) descent, and no holding LAM or elsewhere.

Actually they did 1 circuit of LAM, and the descent was indeed continuous.

Flightman, you seem to have inside information (?). If the descent was continuous, even in the hold at Lambourne, was it steep enough to avoid significant spool-up when they were not slowing down?

Quote (#66):
What we do not yet know is: what happened earlier during the descent and approach? Could the demand for more thrust at T+0 have been the first since top-of-descent? On a daytime arrival into LHR, that would be (sadly) a very rare event. So, assuming thrust above idle was needed earlier (e.g., on initial approach, or to stabilise at 160 kts till 4 miles for ATC spacing) how did the engines respond to the autothrottle demands?
If the engines had gradually been contaminated with dirty or waxed fuel, would this not have been revealed earlier? Why did the two engines suffer no apparent problems until 600 ft, and then - despite feeding from separate tanks - only 8 seconds apart?
Unquote.

Also, would the increased TAT and SAT in at least 20 minutes of the descent not have de-waxed the fuel, as has previously been suggested?

I know on (most) N1-managed engines, FADEC will run closed-loop on N1. Maybe someone can enlighten us on EPR machines. :confused:

Somewhere I think I remember reading that there is a difference in the physical fuel flow to the left and right engines - something to do with the oil/fuel heat exchanger?

Is this correct or is my memeory up the spout?

Tree:
Jet A1 will freeze at -47 C. Considering the amount of fuel 777 was carrying SAT -60 is not cold enough to freeze it on the way from PEK to LHR. In the NW parts of Russia SAT has been around -70 (~FL390) lately, but even that is not cold enough. I have been flying (A340) many times in temperatures like -76 SAT and even in that temperature it takes hours before fuel temp in outer tanks (wing tip) drop below -40. In inner tanks temperatures are then still well over -40 deg.

Somewhere I think I remember reading that there is a difference in the physical fuel flow to the left and right engines - something to do with the oil/fuel heat exchanger?

Is this correct or is my memeory up the spout?

No. The engine fuel/oil heat exchanger is on the engine. It is the same on all Trents.

What is confusing you is that the hydraulic oil pump case drain filter heat exchangers are in the fuel tanks. Two in one wing tank and one in the other. These cool the skydrol that runs through them, and in so doing impart heat to the fuel in the tank. This heat is nearly not measurable.

I heard today that the software on the FADECS was upgraded two days prior to the accident. Still clueless, but interesting none the less.

This "incident" is going to cost the industry Billions.
 

This "incident" is going to cost the industry Billions. Yes it is!

An incident like this due to low fuel temperatures will re-write the book on long cold flights, fly lower and faster.

If the fact that BA38 managed to fly over four thousand miles and augered in just a quarter of a mile short of the runway with no prior indication anything was wrong is an indication that all the sensing of fuel temperatures and metering is a load of bollocks as currently applied.

Looking at this incident another way, all the sophisticated systems on the 777 made the aircraft perform flawlessly for over eleven hours, then, due to some "fuel" temperature unforseen circumstance an engine quit.

Hey I can understand that, these things happen.

What I am having some difficulty believing that the second engine, with a different fuel supply and totally seperate sensing and control system quit FIVE SECONDS after the first one did!!!!



Waiting for the final report......

Every Anorak and those of the misguided religions that have posted complete twaddle, disguised as factual opinion, should be set in the stocks and pounded with cabbages, tomatoes and absolutely anything smelly that comes to hand, after the final report is in :ugh:

Tree:
 

The U.S. Antarctic program used Diesel Fuel Arctic (DFA) for everything
(jets, turboprops and helos, diesels of every size, and furnaces) up to some time in the 1990s, when they went to the US military standard, JP-8.

I know of no aircraft mishaps there from fuel temperature problems with either fuel. C-130 ops are conducted down to -65F at the surface, limited by landing gear fragility. At those temps, engines must be left running - cold starts have a good possibility of prop seal damage, and there are no hangars, heated or otherwise, at Spole.

A380focal
On this basis if the throttles didn't move in line with the FADEC demand the problem could have been quietly brewing for hours in the cruise without any indication to the flight deck crew.
During the latter part of the flight the fuel flow in the cruise would have been about the same as on final approach.
One other point we don't know how much cargo was on the aircraft but 130ish passengers would equate to about 12 tonnes payload. A 777 at a low weight could well be at or above FL400. Does anyone know the flight profile of the aircraft?

Seldomfixit & soggy_cabbage
 

Although I am not an anorak, I did offer to kiss Danny's left buttock if I am wrong and fuel icing/waxing didnt cause the incident. Will that do?

I would have been surprised if there WASN'T a gap between the two events. If they had occurred simultaneously the chances of it being fuel related would be extremely slim and the chances of it being a common-mode software / control failure much higher.

Do civvy airlines use an icing inhibitor such as FSII? and would this be effective?

I am led to believe that the final cruising level entering UK airspace was FL400 ...


JD
:)

Indeed. The FADEC doesn't even have to be on the engine. Providing it gets the neccesary digital inputs it can be located anywhere on the aircraft

Answers to some of the moderately technical questions that crop up about the 777 can be found here:

http://www.boeing.com/commercial/airports/777.htm

To try to clarify:

The term "freezing point" for Jet-A1 is maybe somewhat misleading. It's basically the temperature below where the normally "transparent" fuel shows its first traces of "milkiness". Diesel guys refer to this as the Cloud Point. The flow is not impaired at this temperature.

The dangeruos temperature is where the fuel has thickened so much it's practically not a liquid anymore. Diesel guys refer to this as the CFPP or Cold Filter Plugging Point. For Jet-A1, I've not seen a corresponding term, presumably because this temperature range below the "freezing point" is a no-go area that provides the required safety margin.

For diesel, the temperature margin between the CP and CFPP can be between -5 and -15 degrees C depending on fuel composition, fuel system design and probably other factors as well. In land vehicles one may utilize this margin, but it pays to be prepared for filter clogging. I saw a corresponding figure of -6 degrees C for Jet-A1, but there is obviously some variation in this case too.

Snowfalcon is 100% correct. The reference to diesel is interesting because diesel contamination is known to raise the freezing point of aviation fuels. The following is an interesting read (although its a promo):

http://www.sartec.co.uk/News/mod-pr.htm

Re Diesel contamination
 

Pinkman. Just to get it straight in my mind. We seem to have a suggestion of a type of fuel contamination that can raise the freeze point. So this allows high power for take-off climb and cruise, but also allows significant waxing after a long cold soak at altitude (and the temps were apparently rather low that day). From TOD to Lambourne engines may well have been idle all the way, if there were any restriction it wasn't enough to snuff them out at low power. But in 35 years of operating to Heathrow I don't think I ever did an idle descent from cruise level to finals, especially not on a windy day like Jan 17. As everyone knows, ATC can't maintain flow in headwinds, the rules don't allow them to (constant distance spacing = increased time separation); even if they didn't hold at LAM (and we don't seem to know that for sure), or even if they descended continuously in the hold, I can't believe they didn't do the obligatory shuffle 270 deg off LAM level at FL 70. That would have required modest EPR, similar to final approach. But the engines responded then. Is it the suggestion that the higher fuel flow then dislodged a 'plug' of wax (?) from wherever it was sitting happily to somewhere closer to the engines, to then move fatally somewhere else when the final power demand was made (rather like a deep vein thrombosis moves from the legs to the heart or lungs, as I understand it)? I might even buy it.

Thanks for that last link... good reading!
Diesel contamination levels down to 0.2% were used to cross-check automatic methods!

Further... The Fuel Temp warning on the 777 has a triggerpoint 3degC higher than the temperature set by the crew (via the CDU).

This also increases the likelihood that freezing will be detected before it starts to cause a problem.

gonebutnotforgotten (post#185), the only thing you have not covered in your discussion of the descent from TOD to 600ft is the denouement.

Is it plausible that the 'plug of wax' (which you liken to an embolus) could affect both engines, when they are being fed from separate autonomous tanks? If not, there would have to be two plugs of wax evolving separately and independently.

Plausible enough, but is it likely that they would each migrate to the two engines and cause their separate failures at an interval of only 8 seconds?

You don't believe it either, do you?

Chris

Re-post
 

I first posted this ten days ago, but I just love repeating myself....

It will be fuel contamination

--------------------------------------------------------------------------------

China has a $2,000,000,0000 a year industry making fakes. Lest you think this is just the odd Rolex or Gucci bag for a laugh the China PLC inventory includes millions of fake car and truck parts not caring one whit how many people are killed thereby. More sinister is the the fake pharmaceuticals which often are not simply benign white chalk pills but random chemicals found out back in the garage, once again not caring one whit who or how many die.

In the case at hand the only other remotely possible explanations are a multiple bird strike of epic proportions or fuel exhaustion. Give credence to the former if you like, to the latter, well, you will need a lower opinion of BA aircrew than is common.

No, someone will have passed off a few million litres of doctored diesel fuel as jet fuel. This fake fuel of course is not tested for fuel freezing. Fuel freezing will then have occurred during the lengthy flight from China (not ice formation, but wax components of the fuel reverting to solid) and this slurry sank to the bottom of the tanks. On final with perhaps 4 tons or so sloshing around in near-as-empty tanks this fuel willl have been ingested.

Eh Voila

Have some faith in your hardware is what 10,000 hours on the 777 has taught me. There will be human skulduggery at root here somewhere

Ok then, why did no other China originating aircraft have problems ?

Of ALL the questions, in ALL the gin joints, you HAD to ask that one :eek:

Embolism?
 

Chris - I was just trying to make sense of the previous posts, and yes, it is pretty unlikely/unprecedented, but same fuel, same temperatures, and very nearly identical tanks (one hydraulic heat exchanger versus two) means that the independence may not be what it seems. As has been pointed out earlier, the fact that there was a small differnece in the reactions of the two engines means that the electronic explanations may be less likely than the 'mechanical' ones. In the end I'm as baffled as everyone else, this is a fascinating puzzle but it feels we may be zeroing in on the answer.

to me it feels like you're tunneling in on the answer.

Hope to hear more soon (from the AAIB).

Gentlemen. The AAIB are zeroing in on the answers, probably a combination of several factors if history teaches us anything. You (the speculators rather than the sensible ' hang on a minute' ones) are waffling to pass an idle moment.

If by some bizarre coincidence one of you happens to be right, please don't expect me to place any trust in your opinion next time.

Yes, its great, isn't it. But I tell you what.. irrespective of what the final outcome is, 1) it has raised the profile of aviation fuel quality, 2) it has raised awareness of the importance of managing unusual environmental conditions. Can raising awareness be a bad thing? Isn't that what PPrune is about?

Yes, but only if the fuel is on spec. If the fuel is off spec, how would you, or the machine know what that temperature relates to?

Because no aircraft flew exactly the same route with exactly the same fuel at exactly the same time. If this flight had landed 5 minutes earlier, would it have in fact happened? Was it the same fuel in fact? Was it a bowser or a hydrant servicer? Could it have been a slug of water when tanks were switched?. Is there only one supplier to all aircraft? Was there maintenance done on the fuel system or the bowser? etc. etc. The AAIB will look into all this.

gonebutnotforgotten: Yes, thats about what I am supposing - but like anyone else, I have no idea really. I dont like the word "plug". I know that when I used to do the test in the lab, the wax crystals settled out. Maybe it was both ice and wax. Maybe it was water. Maybe it wasn't fuel at all. I just don't know. Its just one of a number of hypotheses. All I am saying is, the facts that we know argue more strongly for it than against it.

Pinkman

I dislike these "False Choice" arguments. We don't know the cause at this stage.

I can think of all sorts of other reasons the engines might not have responded, for example, differential expansion of fuel control componentry which was apparently at the root of the B737 rudder problem.

Could we please wait and see?

Now who has failed to grasp the significance of the nonlinear system.....

:ok:

I found the following elsewhere:

http://www.aviationweek.com/aw/generic/story_channel.jsp?channel=comm...


http://preview.tinyurl.com/2p2tgy
"Sources close to the investigation also tell The DAILY that British
Airways engineers have been collecting fuel samples from every flight
emanating from China. The sample collection, plus comments from the
AAIB indicating the aircraft had "adequate" fuel remaining on board at
the time of the crash, is believed to point toward suspicions of a
heavier-than-fuel contaminant being present. Theories propounded by
crew include the possible presence of water in the tanks that, having
become frozen during the intense cold-soak period of the flight,
partially melted and formed a slush that could have partially blocked
the fuel lines.

Sources also tell The DAILY that upper air temperatures over Russia
and northern Europe were extremely cold on the day of the accident.
Information from other crews coming from Asia on Jan. 17 encountered
extremely low temperatures in the -70 to -75 degrees C. range,
resulting in fuel temperatures dipping into the -40s. European upper
air temperatures also indicate the last 6.5 hours of the inbound China
flight would have been flown at an outside air temperature of -60 deg.
C. or lower. Although this would have resulted in fuel temperatures on
approach in the -35 degrees C range, this would not normally
constitute a problem unless, potentially, contaminants were present."

And it's been said (not by me) that "Sources close to the investigation" means a leak from the AAIB investigation. True? Likely? Or just yet more speculation & rumour-mongering?

In Journalist-speak, "sources close to the investigation" can also mean anybody the AAIB has had any dealings with including the mini cab driver who overheard some gossip driving the investigator to LHR.

"Sources WITHIN the investigation" might be slightly more interesting as weasel words...but that's not the case here.

Bobbsy

Why would they do that? Why dont they just test the retention sample from BA038 on that day? Unless there isnt one; or unless they have ongoing concerns; and does "emanating from China" mean "after its arrived" or "before it takes off"?

Low temperature operation
 

Speaking as a non driver (at least for the last 50 years), but who spent many years trying to make various bits of A/C equipment work at -60 and beyond. May I ask what other equipment is in the fuel lines, apart from filters. Are there turbine type flowmeters for example. and rotational type valves. What has to happen to increase fuel flow.

Isn't it just deliciously ironic that Boeing brought out a Service Letter reference worldwide Fuel Specifications on the 18/01/08?

Thanks, you've confirmed my suspicion that rather too much was probably being read into the Aviation Week report.

PROJECT MECHDo you mean when a major event took place only the previous day? As you will understand, an important Service Letter would have been prepared carefully over many days and it was purely coincidental that such an unfortunate incident took place the previous day. Boeing and all it's staff are working assiduously ... etcetera.

Why did no other China operating aircraft have problems?
 

There's a simple solution you've all missed. Sure China is notorious for counterfeits. But why just the fuel? Take a very close look at that B777. Can you be sure it hasn't been replaced with an ALMOST PERFECT REPLICA while on the ground in China? And if it hadn't been for that pesky fuel system they'd have gotten away with it too...

Glide performance of 777?
 

So as to avoid any speculation on a probable cause, I'd like to find out more about the glide performance of the 777.

Can a 777 pilot please comment...

Most machines I've flown (737 the biggest) have glide ratios of between 2 and 3 nm per 1000 ft in the clean configuration.
Fully configured this normally halves.

Argument: When the engines failed to respond (or thrust decreased) the aircraft was at 600' and 2nm.

If the glide performance of a configured 777 is say 1.5nm per 1000' (Im guessing!) the aircraft would have flown another 0.9nm (and obviously not made it)

Above assumes that the aircraft was already at glide speed and any extra speed would obviously send it farther (but I doubt all the way to the airfield).

We do however know that the engines were turning and it seems obvious that they were producing some amount of thrust till touchdown.

Could a 777 pilots perhaps comment on what amount of power would be needed to get the 777 to go 2nm from 600' in the landing config?

I understand that knowing a rough power setting is not really relevant to the incident, but it will certainly help pass the time while we wait on the AAIB :)

PP