The simple conclusion with regard to the Sukhoi crash, is that there was a serious lapse of aviating and navigating professionalism. There is little indication at this point, of mechanical failure being a major factor.
The snippets of information slowly being gathered - such as no pax manifest being drawn up - show a culture of "joyriding" and casualness associated with the entire flight.
I'll wager that the final report produces a record of casualness towards the flight plan on the part of the Captain and the co-pilot.
Perhaps there was no complete and utter recklessness, as fullforward is stating - but it's totally obvious that after setting a descending flight path, the Captain and crew were either unaware of the precise position of the mountain, as regards their intended path - or perhaps, because of lax cockpit drill, visitors to the cockpit distracted the Captain and co-pilot from giving their full attention to navigation, at a time when they needed 110% attention to navigation.
There is a subtle increase in complacency and a corresponding lowering of professionalism in many skilled people as they age, and as their experience, and "hours in the seat" increases.
It's a not-uncommon factor to find that many people involved in disasters involving fatalities, and serious crashes involving major injury, have good skills that should otherwise have ensured that they did not come to grief.
The old adage that "complacency breeds contempt" is an adage that is well-founded. Casualness and complacency are extremely subtle human factors that just creep up on you, when you continue to do the same complex job continuously.
I am often dumbfounded at how otherwise highly skilled, and supposedly highly professional people, with extensive experience, initiate disasters - that have as their root cause, simple acts of negligence, casualness, and complacency, that led to the disaster.
We, as humans, tend to develop habits over a long period of time, that degrade the intense professional skills levels required, when complex machines are being operated.
We have to continually guard against those habits degenerating into habits of complacency that take us into areas of extreme danger.