The small fixed wing pilot is most responsible for the mid-air collision. The Visual flight rule is see and avoid. Unfortunately the fixed wing a/c was a low wing and thus vision is obstructed. He was approaching the rotorwing a/c from the right rear at a higher altitude. The rotor wing may or may not have been climbing or may have been in level flight. Most likely the rotor wing pilot uses a pre-planned pre-filed flight path. There are no VFR requirements to file a detailed flight plan. Usually a business such as this do file something with the controlling authority. Sad, very sad.