Primary finding
Probable cause
The downward flexing of the standing helicopter's main rotor blades and subsequent impact with its tail boom as a result of another helicopter's rotor blade's vortices. .
Investigator assessment
Analysis narrative
The pilot reported that he had just landed and was in the process of shutting the engine down when another company helicopter landed at his 2 o'clock position about 40 to 50 feet away. The vortices created by the second helicopter's main rotor blades caused the main rotor blades of the standing helicopter to flex downward before impacting its tailboom, which resulted in substantial damage to the standing helicopter.
Source record
Factual narrative
The pilot reported that he had just landed and was in the process of shutting the engine down when another company helicopter landed at his 2 o'clock position about 40 to 50 feet away. The vortices created by the second helicopter's main rotor blades caused the main rotor blades of the standing helicopter to flex downward before impacting its tailboom, which resulted in substantial damage to the standing helicopter.