grasping at a different straw
It is suggested that Ba038 was given an unusually long soak at -75degrees.(Around ISA -20 ....more unusual in that it is also suggested that most aircraft on this route took precautions and reduced altitude)
...How many hours would this have been? and did it continue to top of descent? Would all engine internal temperatures be running as much as 20 degrees lower than at the same altitude with a normal OAT of ISA.?
Did it at any time in a long Flight-Idle descent pass through an area of high humidity and low temp (cloud)?
.....We do know that a long taxi at Idle in fog can produce "core-icing", in spite of having engine deicing switched on, which has to be countered by a clearing procedure Thus allowing continued operation without damage occurring.
....Does mild core icing ever occur in flight?preventing acceleration?
....Could an amount of core ice accumulate ,and not be readily shed, on such a descent commencing with a core temp already 20 degrees lower than usual? with normal engine deicing operating at less than 100%?
NOT very likely.If it had happened thus, there would probably be data records,or signs of internal damage. Or the engines would not have run down again after they had succeded in initial acceleration.
...I still think its fuel,plus a bit of wind shear.