Accident Overview
A helicopter engaged in external load operations collided with a tree, resulting in a loss of control and a nose-first descent into the ground. The incident occurred while the helicopter was maneuvering near tall trees with a 78.8-foot-long external load line.
Sequence of Events
The helicopter was conducting external load operations in the vicinity of trees ranging from 80 to 90 feet in height. During the operation, the main rotor impacted a tree. Following the impact, the helicopter descended nose first into the ground.
Engine and Rotor System Data
Data from the Vehicle Engine Monitoring Display (VEMD) recorded a high torque measurement of 146 percent and a low engine drive speed of 184 rpm at the moment of rotor impact. Subsequently, the VEMD recorded a low torque of 5.7 percent, a high engine speed of 511 rpm, and a high temperature of 999°C.
Cause of Engine Overspeed
The main rotor impact with the trees caused the engine's torque to twist apart the engine-to-transmission drive shaft. This failure led to an engine overspeed and over temperature condition.
Operational Context
The operator was using a 78.8-foot-long line for the external load operations. In some cases, this line length placed the main rotor of the helicopter below the treetops of the 80- to 90-foot trees.
Post-Accident Examination
Examination of the helicopter revealed no evidence of a preimpact malfunction or failure of the control system or power plant.