The aircraft was spraying thistles when the accident occurred. There were several areas to be treated on the property. The first area had been completed and the pilot was flying the first swarth run on the next area when the aircraft hit a double wire powerline which culminated in a severe impact with the ground. The investigation revealed that the pilot had been given a map of the property by the property owner. The map had two powerlines depicted but did not show the powerline that the aircraft hit. The span was reported to be about 450 metres and the poles were remote from the point of impact. Prior to commencement of spraying the pilot made an aerial inspection of the area for powerlines and other hazards. He did not identify the powerline that the property owner had neglected to mark on the map. Significant Factors The following factors were considered relevant to the development of the accident: 1. The pilot was not made aware of the existence of the powerline that he hit and he did not see it during his aerial inspection of the property before commencement of spraying. 2. The span of powerline that the aircraft hit was about 450 metres and the poles were remote from the impact point, thus denying the pilot cues as to its existence.