I have been revisiting the fuel system diagram posted by Jet II at post 467, and it shows the LP fuel filter after the FCOC, which also seems to me to be an unusual arrangement.
Anyone out there know why the T800 is like that??
Sooty
This is a normal arrangement, LP Pump - Oil Cooler - LP filter (with bypass) - HP Pump. Nothing unusual in that system and it's comon to all 3 big manufacturers.
Again, where T800 is different is the return circuit of spill flow (that flow delivered to the FMU in excess of what the burnt flow demand is) which is not an inconsiderable amount of fuel. On T800 it spills around the HP system in most other applications it spill around the LP system therefore introducing a large heat source into the FCOC.
Also, it is normal practice to arrange the flow path so that the hottest oil is cooled by the coldest fuel.
However, the effective "fix" is, in my opinion, treating the symptom not the cause, which is essentially fuel with high entrained water content.
Controlled testing of the engine fuel system whereby a "slug" of ice or "snowball" is introduced into the LP inlet is extremely difficult to control and replicate that which develops in the aircraft system.
As has been previously stated the engine fuel system has been optimised within the aircraft flight envelope, I do not know the intimate detail but it appears that there may have been some envelope excursion with BA0038 which the engine fuel system was not designed to accommodate, combined with the upload of fuel that may have had a high water content and the result could be considered as academic.
For information engine fuel system ice testing is carried out at a concentration level of ~260ppm.