The Boeing site discussion of fuel waxing is worth a read. It leads to one question regarding the 777:
"The 777 has a fuel temperature probe located between ribs 9 and 10 of the left main tank. The probe is approximately 12.6 in from the lower wing skin and is located one rib over, approximately 40 in outboard, from the aft boost pump inlet. "
The question is how empty will this tank be when the fuel temp sensor is dry and no longer accurate?
The other part of the Boeing discussion involves the possible mixture of fuel with differing
freezing points in the same tank, and the statement that the fuel fraction with the highest freezing point will start contributing wax crystals to the liquid first. If these crystals behave anything like those in water-alcohol-gasoline mixes, they will tend to pile up like slush on the first obstruction like a filter or orifice, retarding but not entirely blocking flow.
Any informed comment available on this?
The Boeing page is:
http://www.boeing.com/commercial/aeromagazine/aero_16/polar_story.html
scroll down to section 3, "Polar Fuel Management"