CESSNA 172S — Longmont, CO

What happened

The flight instructor and student pilot took off in a Cessna airplane from their home airport and proceeded north to a practice area to perform practice maneuvers. The Sonex pilot departed from an airport east of the practice area about 5 minutes earlier and proceeded westbound toward the vicinity of the Cessna. Both airplanes climbed to 7,000 - 7,500 ft mean sea level (msl) and operated under visual flight rules (VFR).

When the Cessna reached the practice area, it made a left 360° turn consistent with a clearing turn, which according to the flight school was standard procedure. On completing the turn, the Cessna proceeded eastbound. The Sonex approached the same area from the east and tracked west-northwest toward the vicinity of the Cessna. The flight track data showed the two airplanes come together at an altitude of about 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. Both airplanes came down in fields about 2,400 ft apart and were destroyed on impact with terrain. Postaccident examination of both airplanes showed no preaccident failures or malfunctions that would have precluded their normal operations.

The Cessna was equipped with automatic dependent surveillance - broadcast (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. An examination of the GPS and transponder from the Sonex determined that the units were configured to not transmit position data via ADS-B. Investigators were unable to determine the exact configuration of the cockpit traffic displays for the Cessna.

The sun was in the east (108o) about 24° above the horizon. A visibility study showed that the respective airplanes would have traversed the respective windscreens from right to left and left to right over the 60 seconds before the collision. However, the instrument panel, canopy frame, compass, and sun glare would have obscured the view of each pilot presenting challenges to detecting the respective airplanes.

Toxicology specimens from the student pilot revealed Cetirizine in liver and muscle tissue. Cetirizine is an antihistamine available over the counter and is used to treat allergy symptoms. It may cause drowsiness. However, it is uncertain whether the student pilot was experiencing any sedating effects of this medication at the time of the accident. Given the circumstances of the accident, including the presence of a qualified flight instructor, it was unlikely that the student pilot’s Cetirizine use contributed to the collision.

An editorial "what led to it / how to avoid it" analysis for this accident is generated separately and will appear here.