Read
http://www.pristaerospace.co/hi-flas...ils/index.html on how dissolved water comes out of solution as avaition fuel is cooled. This explains where the water came from initially. (AAIB reports 70ppm dissolved water in the fuel) The resultant ice and supercooled water then adheres to pipework in the fuel delivery system, including the small bore tubing in the inlet to the FOHE. (anyone know the ID of these tubes as they appear to be very small bore to me? ) In tests the delta P across the FOHE was observed at levels in excess of 9 barg suggesting tube blockage. (in the NTSB pic of the FOHE tube sheet, after recent testing, many of the tubes are plugged) If the fuel is heated the water remains dissolved and is not problematic in the fuel delivery system.
If you click on "history" on the above website the first instance of this type of failure is reported in a B52 in 1958, where 5 of the eight engines stopped.
Re anti icing additives the Shell Avaition website declares that anti icing additive is mandatory on all military aircraft fuel but is not necessary on commercial aircraft where the fuel is heated.
Was the fuel on the aircraft in question too cold for too long? Does cold unheated fuel on shorter flights deposit ice in the fuel system pipework and is not a problem because not enough of it has formed before the flight ends safely? If the fuel is heated what is the lowest safe temperature before the dissolved water starts to leave the fuel and become an operational problem?
As a retired engineer I am interested in this problem as I flew the same route as a passenger 8 hours behind BA038. I was in a 747 and the OAT west of the Urals was -76 C for hours. My flight was uneventful. I keep asking myself why?