Shortly after takeoff, a loud noise was heard and sparks were observed coming from the right side of the right engine. The aircrew attempted to feather the right engine, but it would not feather. They were unable to maintain altitude and descended into trees. After striking trees, the plane came to rest on the roof of a house. The aircraft burst into flames about 5 to 10 minutes after the crash. A police officer that had responded and had climbed onto the roof was reportedly thrown off by an explosion. He received minor injuries. An examination of the right engine revealed that one blade of the model HC-82XG propeller did not feather and was free to move. The retaining clamp on this blade was cracked and had a portion missing. A metallurgical examination revealed that it had failed from high cycle fatigue. Hartzell Propeller Service Bulletin, No 126, dated 12/9/80, recommended that this clamp (an old model) be replaced by a new improved type. No other preimpact failures were found.