DEN86MA129

At 1042 MDT, the flt rprtd mod turbc at FL 240, but elected to remain at that alt. At 1055, they were clrd to dscnd at plt's descretion to maint 12,000'. Aprx 8 min later, shortly after bgng a dscnt, the flt was instructed to chg freq; BUT21 secs later, they replied 'standby please,' then radio & radar contact were lost. Wreckage was fnd aprx 26 mi east of the destn arpt in mtns. An exam revealed the empennage had sepd in flt; pieces of it were fnd up to 1 mi away with indcnof overload failure. There was evidence that: engs were not operating at gnd impact, ignition sws were engaged; l eng start sw was in the 'air' start psn & r sw was beyond the 'ground' start psn; r prop was feathered; pax oxygen masks were deployed, indicating cabin had depressurized abv 15,000'. Wx info indcd cld bases at 10,000' with IMC & turbc to 25,000', mixed icg fm 20,000' to 25,000', lgt rain/snw shwrs, widely scat tstms; aprx 15 mi south, 4' to 5' of hail fellat aprx that time. Tpe 331 engs had history of flameouts due to ice injestion caused by imp use of anti-ice/ignition.