What happened
During dusk operations under visual meteorological conditions, a Piper PA-31T (Cheyenne) and a Cessna 172P (Skyhawk) collided while in the cruise phase of flight. The Cheyenne had departed from an airport northwest of Denver, traveling at 7,800 feet with a ground speed of 230 knots. Simultaneously, the Skyhawk was traveling from a southern airport toward Cheyenne, Wyoming, at 7,300 feet. After receiving clearance to climb to 8,500 feet, the Skyhawk was positioned within a designated VFR flyway, whereas the Cheyenne was not.
As the two aircraft converged, air traffic control attempted to verify the altitude of the Cheyenne. The pilot reported being at 7,600 feet. Although the controller issued a traffic advisory, the pilot of the Cheyenne did not acknowledge the instruction. Following the collision, both aircraft left controlled flight. The Skyhawk impacted a residence, while the Cheyenne fell inverted into a backyard. Debris from the wreckage was distributed across a 24-square-block area in western Denver.
Findings
Investigation of the wreckage revealed physical evidence of the impact, including four distinct slashes on the Cheyenne's right engine nacelle, cabin, empennage, and tail cone, which were consistent with propeller strikes. A critical factor identified was that the Cheyenne's altitude encoder was transmitting data intermittently. This issue had been noted by the pilot during a similar flight three days prior to the accident.
Technical examination of the Cheyenne's equipment uncovered a cold solder connection on pin 8 of the 15-pin altimeter connector. This faulty connection caused the intermittent altitude transmissions observed by radar. Once the connection was repaired via resoldering, the altimeter, encoder, and altitude serializer functioned normally.