On Saturday, July 24, 1993, at 0953 eastern daylight time, a Piper PA 28 180, N9044J, and a Piper PA 38 112, N91357, collided during final approach to runway 26 at Pittsfield Municipal Airport, Pittsfield, Massachusetts. The pilot of the PA 28 180 was not injured, two of his three passengers were not injured, while the other passenger received minor injuries. The pilot of the PA 38 112, the sole occupant, was not injured. Visual meteorological conditions prevailed and a flight plan was not filed by either pilot. Both aircraft were substantially damaged and were operated under 14 CFR 91. Both aircraft were on final approach to runway 26 when they collided about one quarter mile from the runway threshold about 200 feet above the ground. The pilot of the PA 38 reported that she overflew the runway at 3000 feet and entered a right downwind for the runway. She stated that she announced her position on the unicom frequency. According to her, she was number three for landing. She stated that she was, "on a stabilized approach, on the glide path at 70 knots, I heard a clunk and felt a downward push. I looked up and saw the propeller of another aircraft above and to my left. The aircraft was overtaking me and descending on top of me. I immediately attempted to initiate a descending right turn to separate us...I saw the prop come down and hit my engine block. I fought to maintain control...and was able to land straight ahead on runway 26." The pilot of the PA 28 stated that he entered the downwind leg for right hand traffic to runway 26. He stated that he was about 100 feet high on the initial approach, and he reported his position on the unicom frequency. He stated that he was looking at the aircraft which touched down and was taxiing on the same runway. He said that he reduced the power for landing as he was established on the VASI ( visual approach slope indicator) and about 100 to 200 feet above the runway threshold. Shortly thereafter, he heard a bang followed by an impact and the airplane went inverted. He stated that all the occupants on his airplane were hanging upside down until the airplane slid to a stop off the side of the runway when he was able to free himself and the occupants. Upon exiting the airplane he noticed the propeller of his airplane had sliced through the left side windshield of the PA 38. The pilot stated that this accident could have been prevented if he had established two way radio communications. There were several witnesses who saw the two aircraft on final approach. Two of the witnesses who were monitoring the unicom frequency reported that they only heard the pilot of the PA 38 radio her position. They stated that the PA 28 which was about 50 feet above the other aircraft descended onto that airplane. They remained together, collided with the runway, and veered off to the left of the runway. The FAA Inspector who examined the wreckage stated that the investigation revealed that the radios of the PA 28 were tuned to the unicom of the departure airport where that pilot had just departed, and not the unicom frequency of the arrival airport which is 122.7. One of the witnesses who flies at the same airport reported that there have been a few pilots who sometimes confuse the two frequencies.