THE AIRCREW REPORTED THAT DURING FLT AT 6000 FT MSL, THEY ENCOUNTERED ICING CONDITIONS & USED THE DE-ICE & ANTI-ICE EQUIPMENT. AFTER THEY DESCENDED & WERE CLEAR OF ICING, THEY DEACTIVATED THE DE-ICE & ANTI-ICE EQUIPMENT.THE CAPT SAID HECHECKED THE PROP SPINNERS & NOTED A SMALL BUILDUP OF ICE, WHICH HE CONSIDERED AS MINIMAL, & TURNED OFF THE CONTINUOUS IGNITION. SHORTLY THEREAFTER WHILE ON FINAL APCH AT APRX 1000 FT AGL & 1 TO 1.5 MI FROM THE ARPT, THE R ENG LOST POWER WITHOUT WARNING. THE COPLT FEATHERED THE R PROP & THE APCH WAS CONTINUED. HOWEVER, AT ABOUT 200 FT AGL THE OTHER ENG ALSO LOST POWER. THE ACFT WAS LANDED WITHOUT FURTHER INCIDENT. DURING AN INVESTIGATION, ICE WAS FOUND ON THE GROUND UNDER THE WINGS. NO MECHANICAL PROBLEMS OR FUEL CONTAMINATION WERE FND. THE ACFT HAD A HISTORY OF FLAMEOUTS DUE TO ICE BUILDUP & RELEASE FROM THE SPINNERS. IGNITION SW LABELED 'NORM', 'CONT' & 'OVRD.' TO OBTAIN CONTINUOUS IGNITION IN FLT, THE SWITCH MUST HAVE BEEN IN 'OVRD.' NO SPECIFIC WARNING IN FLT MANUAL TO USE CONTINUOUS IGNITION (OVRD) IN ICING COND.