The pilot started the engine and set about 75 percent RPM. He then experienced an urgent call of nature and left the helicopter unattended with the engine running. While the pilot was absent, the passenger boarded the helicopter (although the pilot had apparently told him not to do so). As the pilot was returning to the helicopter, he saw it become airborne at the same time as the passenger exited the helicopter. The helicopter rolled on to its side and was substantially damaged. The passenger could not recall whether he had moved any of the cockpit controls.
