What happened
A flight mission intended for aerial imagery of forest vegetation ended in a fatal accident when the aircraft entered a rapid descent. During the mission, the aircraft reached an altitude of approximately 16,100 feet MSL and achieved a groundspeed of 209 knots. Shortly thereafter, the aircraft's speed dropped to 93 knots, accompanied by a 500-foot loss in altitude while maintaining a steady heading. Following this period, the aircraft entered a steep descent and a right-hand turn. The crew transmitted emergency distress calls to air traffic control, specifically stating that the aircraft was in a spin.
A witness near the crash site observed the aircraft descending at a high rate of speed with its nose pointed downward, followed by a rapid rotation around its longitudinal axis. The wreckage of the aircraft was recovered from a remote area characterized by wooded terrain and wetlands. The impact occurred in a nose-low vertical attitude at high velocity. All primary components of the aircraft remained at the site of the crash.
Findings
An investigation into the airframe, engines, and propellers found no evidence of mechanical failures or malfunctions that would have prevented standard operation. Performance studies indicated that as the aircraft pitched downward, the normal load factor dropped from 1.6 to below 1 G. This rapid reduction in load factor is a characteristic indicator of a stall occurring when the wing exceeds its critical angle of attack.
Evidence suggests that the pilot likely failed to maintain sufficient airspeed, leading to a stall and a subsequent spin during uncoordinated flight. While the exact nature of the pilot's control inputs during the stall remains undetermined, the aircraft's Pilot Operating Handbook does not authorize spins and lacks specific procedures for recovering from an unintentional spin.