What happened
The aircraft began to settle with power during the takeoff phase while carrying a load of chemicals. The pilot faced a decision regarding an obstacle ahead and elected to fly over a fence rather than through it. However, pulling the collective resulted in a loss of main rotor rotation, causing the aircraft to stop flying. During an attempt to flare, the tail boom struck the ground. The impact caused the main blades to flex and sever the tail structure.
The investigation
The mechanical analysis focused on the sequence of events leading to the structural failure. Examination confirmed that the loss of main rotor rotation occurred immediately after the pilot applied collective pitch during the low-speed flight phase. This control input led directly to the loss of lift and the subsequent impact with the ground obstacle.
Findings
Contributing factors included the heavy load configuration and the pilot's decision-making process regarding the fence clearance. The primary causal factor was loss of main rotor rotation due to excessive collective pitch application at low airspeed, which resulted in a hard landing and structural failure of the tail boom.