Primary finding
Probable cause
For occurrence #1 - inadequate supervision by the operator in launching a hazardous mission without an adequate sling/harness, the pilot's poor judgement in accepting and continuing the mission into low light conditions, and the crewmember's inadvertent release of his hold of the nylon strap. For occurrences #2-4 - failure of the tail rotor drive shaft as a result of entanglement of an unsecured nylon strap.