Colorado Aviation Accidents & Incidents

HISTORY OF FLIGHTOn September 17, 2022, about 0853 mountain daylight time, a Cessna 172S, N2117Y, and a Sonex Aircraft Xenos, N255BF, were destroyed when they were involved in a mid-air collision near Longmont, Colorado. The flight instructor and student pilot aboard the Cessna and the pilot aboard the Sonex sustained fatal injuries. The Cessna was operated as Title 14 Code of Federal Regulations Part 91 instructional flight. The Sonex was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

Per the flight school, the flight instructor and student pilot took off from the Rocky Mountain Metropolitan Airport (BJC), Broomfield, Colorado, and proceeded north to a practice area near Longmont to perform practice maneuvers. A review of air traffic control (ATC) flight track data showed that the Cessna departed BJC about 0843 and proceeded north toward Longmont.

The Sonex departed Platte Valley Airpark (18V), Hudson, Colorado, about 0838 and proceeded westbound toward the Longmont area. Both airplanes climbed to about 7,000-7,500 ft msl and were operating under VFR.

On reaching the practice area, the Cessna made a left 360° clearing turn, which according to the flight school was standard procedure. On completing the turn, the Cessna made a right turn just east of Niwot, Colorado, and proceeded eastbound. The Sonex approached from the east and tracked west-northwest passing about 4 miles north of Erie, Colorado, and continued toward a point about 1 mile east of Niwot. The flight track data of the two airplanes merged at 08:53:01 at an altitude of 6,939 ft msl and subsequently showed both airplanes rapidly descend. Fragmented sections of the outboard left wings of both airplanes were found in a field below the point where the two flight tracks merged.

Figure 1. Sonex and Cessna Airplanes’ Flight Tracks.

At the time of the accident, both airplanes transmitted a transponder code of 1200 (VFR) and neither airplane was in radio contact, nor were they required to be in contact, with ATC. Both airplanes operated within the Mode-C veil of the Denver International Airport Class B airspace that required ADS-B “out” transmissions. AIRCRAFT INFORMATIONThe Cessna was equipped with ADS-B “in/out” equipment and transmitted ADS-B data during the accident flight. The Sonex did not transmit ADS-B data during the accident flight; ATC records indicated the Sonex last transmitted ADS-B data on July 14, 2022.

The last three flight instructors to fly the Cessna reported no maintenance issues with the airplane and that the ADS-B equipment functioned properly. METEOROLOGICAL INFORMATIONAt the time of the accident and relevant to the accident location, the sun was at an azimuth of 108.38o and an elevation to the horizon of 23.63o. AIRPORT INFORMATIONThe Cessna was equipped with ADS-B “in/out” equipment and transmitted ADS-B data during the accident flight. The Sonex did not transmit ADS-B data during the accident flight; ATC records indicated the