What happened
On July 3, 2020, a Cessna 172, registration N6929H, was involved in an accident near Alpine, Utah. The flight departed from South Valley Regional Airport (U42) at 06:37 mountain daylight time. Radar tracking showed the aircraft initially flew south, climbing to approximately 6,200 feet near the western edge of Utah Lake. The aircraft then turned northeast across the lake, reaching an altitude of 7,100 feet. After further climbing to 8,250 feet, the aircraft turned north, then later turned 270 degrees to a west/northwest heading. The aircraft disappeared from radar at approximately 07:22.
A witness near the accident site observed the airplane approaching a canyon on a northwest heading. The witness noted the aircraft appeared too low to clear the terrain and observed it enter a tight, right banking turn within the canyon. Following a 180-degree turn, the aircraft leveled off, experienced wing-tip oscillations, and entered a clockwise, corkscrew spin. The aircraft then descended in a vertical, nose-down attitude. The witness reported the engine sound remained constant until the vertical descent began, at which point the noise started to oscillate.
The accident resulted in 4 fatal injuries, involving the pilot and three passengers.
The investigation
First responders found all aircraft components within approximately 100 feet of the main wreckage. There was no smell of fuel at the site, and the wing tanks appeared dry, though hydraulic deformation was present on both tanks.
An examination of the engine showed the crankshaft could rotate freely in both directions, with confirmed valve train continuity and thumb compression on all four cylinders. The propeller had separated at the crankshaft flange, showing torsional overload signatures. One propeller blade exhibited significant leading-edge gouging, torsional twisting, and trailing edge