The air taxi pilot lost control of the airplane and crashed during the second aborted VFR approach. While the pilot said VFR conditions existed, her passengers and witnesses on the ground said the visibility was less than one mile. The passengers said the airplane's windshield and wings were accumulating ice before and during the approaches. The pilot could see outside only by looking out the side windows. One passenger said that during the second approach, he tapped the pilot on her shoulder and told her that the runway was on the right side of the airplane, and pointed to it. He further said that the pilot then did a very steep right turn toward the runway, during which the airplane shuddered violently, stalled, and fell to the ground. The pilot said the engine would only deliver partial power during the second aborted approach. Passengers and persons on the ground said the engine sounded like it was developing full power. During post accident disassembly of the engine, no problems were found that were considered causal to a partial power loss.