Midair Collision Involving Cessna 150 and Cessna 172 During Approach to Runway 35L (N128S)

Incident Overview and Sequence of Events During heavy traffic, the pilot of a Cessna 150, registration N714RS, contacted the tower and was instructed to report on the three-mile left base for Runway 35L. Instead, the pilot reported on the left downwind for Runway 35L and was told to follow a Cessna, registration N9DZ, which was ahead of him on downwind. At 1335:00, the pilot of a Cessna 172, registration N128S, on a straight-in approach, reported three miles final for Runway 35L. He was instructed to follow the Cessna (N9DZ) turning left base in front of him. At 1335:27, the Cessna 150 pilot was told to follow the Cessna 172 on a one-and-a-half-mile final, which he acknowledged. At 1336:29, the Cessna 172 was cleared to land behind N9DZ. As the Cessna 150 turned onto final, it converged with the Cessna 172. The tower controller noted the conflict and asked the Cessna 150 pilot if he could side-step to Runway 35R. The pilot gave a negative reply and was then told to go around, though no specific safety advisory was issued. Approximately eight seconds later, the two aircraft collided about 100 feet over the runway threshold, with the Cessna 150's propeller severing the tail of the Cessna 172. The Cessna 172 crashed on the runway, while the Cessna 150 landed with minor damage.