This August 2008 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
Aircraft: Cessna 172, Cirrus SR22. Injuries: 3 Fatal. Location: Rock Springs, Wyo. Aircraft damage: Destroyed.
What reportedly happened: The Cessna was flown by a student pilot on a local solo flight. The Cirrus was on an IFR flight plan and had been cleared to the airport. Both airplanes were in visual flight conditions. The Cessna was maneuvering northwest of the airport, and the Cirrus was descending toward the airport from the northwest. The air traffic controller working the flight cleared the Cirrus for a visual approach and advised the pilot to switch to the common traffic advisory frequency. About two seconds before the collision, the controller advised the Cirrus of the Cessna at his one o’clock position and 10 miles at 9,500 feet MSL. The Cirrus pilot responded “thank you” and there was no further contact with the Cirrus. Radar data indicates that for the next two minutes, the Cessna maintained a northeasterly heading and climbed to 9,800 feet MSL. About 30 seconds before the collision, the Cessna turned approximately 20° to 30° right and continued on that heading in level flight. During this same two minute and 30 second period, the Cirrus was descending on a heading of about 130° magnetic.
The controller stated that he knew from previous experience and training that Cirrus aircraft are frequently equipped with a traffic avoidance system. He thought that if he gave the pilot a good position on the conflicting traffic, the pilot would be able to see it using his internal system and avoid the other aircraft. These extended discussions with the pilot caused the controller to get behind on some of his other work, and he needed to catch up with other tasks after he finished talking to the Cirrus. Asked when he first saw the conflict alert between the Cirrus and the other aircraft, the controller stated that he was not sure where the aircraft were when the conflict alert activated. He said that based on his observation of the position of the two aircraft, activation of the conflict alert would have been expected. He believed that providing traffic information to the pilot of the Cirrus and allowing the pilot to switch to the advisory frequency would assist in the resolution of the possible conflict because both pilots would then be on the same frequency.
The data depict the two airplanes converging perpendicular to one another and colliding about five nautical miles northwest of the airport at an altitude of about 9,800 feet MSL, or 3,300 feet above the ground. The wreckage of the two airplanes was scattered over an area of about 1,400 feet by 1,500 feet. During examination of the wreckage, transfer marks were identified consistent with the radar-derived collision angle. The Cirrus was equipped with a TCAS-like traffic advisory system that would alert the pilot of transponder equipped aircraft that pose a collision threat within a 0.55-mile radius. Based on the radar data, the system, if turned on, should have generated both an oral and visual traffic advisory starting about 30 seconds before and continuing until impact. It could not be determined whether the unit generated an advisory. It is possible that the geometry between the system’s antenna on top of the Cirrus and the transponder antenna on the bottom of the Cessna prevented the system from generating an advisory, but this could not be confirmed.
Probable cause: The failure of both pilots to see avoid another aircraft.
For more information: NTSB.gov