The aircraft was engaged in a demonstration of the dropping of emergency equipment from low altitude over the sea. This demonstration was being performed for the benefit of television news media personnel. The emergency equipment was contained in a bag which was connected to the aircraft by a static line. On the particular dropping run, the static line became entangled in the spreader bars of a sea anchor which had been packed in the bag. The entanglement prevented the bag from being opened, and it then swung below the aircraft before rising, passing above the horizontal stabiliser and striking the side of the fin and rudder. The static line was cut by the Assistant Dropmaster and the bag fell free. The aircraft remained under control and a safe landing was subsequently carried out. There had been no provision made to secure the anchor spreader bars to prevent their inadvertent deployment. As there had been no other recorded instances of the bars fouling the static line, it was probable that the bag had been incorrectly packed. This may have been related to distractions caused by the film crew during the packing sequence. There had also been no provision made to prevent the static line from blowing behind the bag during the deployment sequence. During the investigation, the pilot claimed that an underlying cause of the incident was harassment by Department of Aviation officers. This harassment included lack of advice and assistance in the development of the emergency dropping equipment, together with unnecessary restrictions being placed on the operation. Detailed interviews conducted with the crew of the aircraft established that all members of the team performed normally on the day. There were no major procedural variations introduced for the particular demonstration, and the operation had been performed successfully in the past. An assessment of the evidence obtained concluded that the alleged harassment was not a factor in the incident.