Accident Overview
A Piper PA-31T Cheyenne and a Cessna 172P Skyhawk collided in midair during cruise flight at dusk in visual meteorological conditions. The Cheyenne, operating under visual flight rules (VFR), had departed from a local airport northwest of Denver and was proceeding direct at 7,800 feet to another local airport south of Denver. Radar data indicated its ground speed was 230 knots. Its altitude encoder was transmitting intermittently.
The Skyhawk, also VFR, had departed from the south airport en route to Cheyenne, Wyoming, at 7,300 feet. The pilot requested and was cleared to climb to 8,500 feet and penetrate Class B airspace. Radar showed its ground speed was 110 knots. The Skyhawk was flying within the suggested VFR flyway; the Cheyenne was not.
Controller Interaction and Collision
The air traffic controller observed the two aircraft converging and asked the Cheyenne pilot for his altitude. The pilot replied that he was at 7,600 feet. The controller immediately issued a traffic advisory, but the Cheyenne pilot did not acknowledge the transmission. Shortly thereafter, both aircraft departed controlled flight.
Crash and Wreckage
The Skyhawk struck a house, and the Cheyenne fell inverted into the backyard of a residence. Wreckage was scattered over a 24-square-block area in west Denver. At the time of the accident, the controller was handling low-altitude en route, arrival, and departure traffic for both airports.
Wreckage examination revealed four slashes, consistent with propeller strikes, on the top of the Cheyenne's right engine nacelle, the cabin above the right wing trailing edge, the empennage at the root of the dorsal fin, and at the tail cone.
Previous Transponder Issue
The Cheyenne had been on a similar flight three days before the collision. During that flight, air traffic control informed the pilot that the transponder was operating intermittently. Recorded radar and voice communications from that flight confirmed that the transponder/encoder operated intermittently and that the pilot was so advised.
Altimeter/Encoder Examination
Examination of the Cheyenne's altimeter/encoder revealed a cold solder connection on pin 8 of the 15-pin altimeter connector. When the wire was resoldered to the pin, the information from the altimeters, encoder, and altitude serializer returned to normal.