TC, do you recall our discussions here on short (high speed) shaft failure? Not sure if this machine uses the 355 setup, I got a feeling it has the two inputs into the MGB, perhaps someone can confirm. If it was an unfortunate case of 2 x unlucky with the short shaft then it would take a few seconds longer to identify this kind of failure as the NR speed dropped and the NGs ran away.
Sawman, thanks for you informative post. Can you postulate any ideas on how this roof was attached to the front wall of this building as that is the bit of the roof that seems to have been pulled out/off its supports first, probably through initial bending of the beams.