138 gallons H20 and stratification
Warning: I'm non-professional; not crew, not engineer - just guest here, thanks.
Interesting posts overnight, many concentrating on the fuel and its state.
Woodpeckers post #280, and others, question whether some 138 gallons of water might have been present in the centre tank and that this, in some form and manner, caused the accident. Problem with this questioning is that the fuel tanks were drained of water at Heathrow before fuelling for the Beijing outboard sector. AAIB Special Bull. 1/2008 states:
"The aircraft's fuel tanks were last checked for water in the fuel on the 15 January 2008 at Heathrow; this was prior to its refuelling for the outboard sector to Beijing."
Additionally, the bulletin states "sump sample taken from the left and right main fuel tanks shortly after the accident revealed no significant quantities of water".
The bulletin further states "Initial results confirm that the fuel conforms to Jet A 1 specifications and that there were no signs of contamination or unusual levels of water content."
We should probably conclude that there was no significant quantity (i.e. something like 138 gallons) of water in the system when it left Heathrow and none when it returned to Heathrow. Even if there had been water in the centre tank before the crash-landing this did not find its way to the wing tanks and then to the engines.
With regard to my earlier posts (195,242), I questioned whether the fuel could stratify due to density and thermal anomalies, in a very cool environment, over an extended period of time, being subjected to high frequency vibration from the engines and so produce layers of liquid that stifle an engine(s) by decreasing the flow rate. Of course, this is a very complex regime, probably one with subtle negative and positive feedbacks, meaning that an initial stratification would progressively mutate into something very different.
Earlier I asked if the water scavenge jet pumps in the wing tanks would destroy stratification. Thanks to Green-dot (#267) for telling us how these pumps operate and for pointing out that detected water causes, "water detection message for a particular tank to show". There was no such message shown during the flight, therefore there was no water, greater than 7 gallons, present in the bottom of the wing tanks and the water scavenge jet pumps did not operate. Any stratification would not have been destroyed by these pumps. Hope I've not missed anything.
However, SyEng (#273) says'
"Stratification: no chance. (following para is general, not 777-specific) Apart from the scavenge jet pumps (if they're not full of FOD), the boost pumps cause plenty of mixing, through their own bypass/cooling flow discharged back into the tank, through swirling/entrainment near the inlet and through collector cell feed/overflow. There is also often fuel returned to tanks from other systems heat exchangers. "
SyEng, you say the paragraph is general, not 777-specific, so is it possible to confirm the destruction of any stratification in the wing tanks by the systems you mention for the 777?
Regards, Tanimbar