The date and timing of the occurrence are approximate only. The aircraft was being used, on behalf of Airservices Australia, to conduct air tests on the static-line used with the PADS supply droping system. A flat-strap static line, with a cone attached, was trailed behind the aircraft and its movement observed on a video camera. The tests indicated that the line could oscillate severely under certain conditions. On one of the test flights the line oscillated until it collided with the rear fuselage. The aircraft was not damaged and its flying characteristics were not effected. The line was pulled in and a normal landing completed. As a result of the tests, the flat-strap line was replaced with a round line and the cone modified. Subsequent tests indicated that this configuration was stable and the oscillations were not repeated.