I think you guys are on the wrong track with all the "ATC clearance" and GPWS talk. I have no doubt that a standard EGPWS would be going ape down in amoungst those mountains. I think it is highly likely they were fully VFR, sightseeing, when they got badly caught-out. EGPWS (or whatever the equiv is in the Sukhoi) is not designed to provide terrain avoidance guidance during low-altitude sightseeing flights. I can even imagine that the system had been disabled, as one would do during a handling demonstration, to prevent the annoying "nuisance" warnings that would be going off eg "bank angle", Too low gear", terrain ahead".