However, the aircraft was moving at roughly 100 m/sec, while propagation of a turbulent flame is only about 20 m/sec.
Whether the flame could still have "crept" forward along the nacelle or the fuselage until it reached the wheel well, remains an open question.
I have personal experience of an aircraft moving at around 150 m/sec suffering a fuel leak and which then ignited and the subsequent fire very, very definitely propagated
forward despite the airspeeds involved . The flame remained stubbornly well and truely attached to the airframe even with IAS's in excess of 350 kts and it subsequently transpired there was significant fire damage to the a**e end of the airframe ....so the oft expressed "fact" that you can outrun a flame front at subsonic speeds seems to me to be hopelessly optimistic.
IMVHO once you have a fuel leak, an ignition source and turbulent flow/flame front all bets as to propagation are off.
Does anyone else fancy having a pop at the pre-existing fire theory
Yes, Occam to
me says - fuel leak, reheat ignites the plume, which then burns forward into the structure. You don't need another ignition source, such as a tyre fire, forward of the leak, to get things going.