The disaster of the Russian military Tu-154 – a few short first thoughts (UPDATED)

It is too early to conclude what happened with this aircraft, but since I have been asked about this by email, here are my own, personal and provisional, thoughts: Mechanical failure: unlikely.  The Tu-154 is a three engine aircraft and an extremely strong beast.  It’s safety record is comparable to most aircraft of its time, even though it was often used in extreme conditions other aircraft types did not have