What happened
On August 10, 2008, at approximately 12:23 mountain daylight time, a Cessna R172K, registration N758NH, and a Cirrus SR22, registration N8341, collided in midair about 5 nautical miles northwest of the Rock Springs-Sweetwater County Airport (RKS) in Wyoming. The collision occurred under visual meteorological conditions.
The Cessna, operated by Franklin Aviation, was on a local solo instructional flight to practice maneuvers. The Cirrus was on a personal cross-country flight from Polson, Montana, operating under instrument flight rules (IFR).
Prior to the impact, an air traffic controller issued traffic advisories to the pilot of the Cirrus regarding multiple aircraft in the area. At 12:20:20, the controller provided a specific traffic advisory for an aircraft at the one o'clock position, 10 miles north, at 9,500 feet. The Cirrus pilot acknowledged the information, and the controller subsequently advised the pilot to switch to the advisory frequency. There was no further contact with the Cirrus.
Radar data indicates the two aircraft were converging nearly perpendicular to one another. The Cessna was maneuvering and climbing from 9,300 to 9,800 feet msl, while the Cirrus was descending from 11,300 to 9,700 feet msl. The collision occurred at an altitude of approximately 9,800 feet msl. The impact resulted in 3 fatal injuries, as the student pilot in the Cessna and both occupants of the Cirrus were killed.
The investigation
Investigators examined the wreckage, which was intermingled and scattered over an area of 1,400 feet by 1,500 feet. Transfer marks on the aircraft, including an indentation on the Cessna's left passenger door and scratches on the wing surfaces, were consistent with the collision geometry identified by radar.
The Cirrus was equipped with an L-3 Avionics Systems SkyWatch SKY497 Traffic Advisory System, designed to alert pilots to potential collision threats within a 0.55-nautical mile horizontal distance. While radar data suggested the system should have generated an oral and visual advisory starting 30 seconds before impact, it could not be determined if the unit actually functioned during the flight. Investigators noted the possibility that antenna shielding between the top-mounted antenna on the Cirrus and the bottom-mounted transponder antenna on the Cessna might have prevented an advisory.
Findings
- The Cessna was performing solo instructional maneuvers, including steep turns and stalls.
- The Cirrus pilot was cleared for a visual approach to Rock Springs.
- The air traffic controller provided traffic advisories but transitioned the pilot to an advisory frequency, which prevented further direct communication via the primary frequency.
- The collision occurred as the two aircraft were on converging paths.