What happened
On July 17, 2015, a SZD-50-3 Puchacz glider was performing a routine aero-tow flight at EPBC. The flight proceeded normally until the aircraft reached the required tow altitude of 700 meters. During the flight, the glider pilot attempted to trigger the release mechanism several times by pulling the release handle, but the glider remained attached to the tow plane.
As the tow aircraft began its descent, a sudden jerk occurred, which simultaneously caused the glider to release from the tow rope. The remainder of the flight was completed without further incident.
The investigation
The investigation focused on the failure of the release mechanism to respond to the pilot's manual inputs. Investigators examined the tow rope and the release hardware to determine why the glider failed to decouple upon the pilot's command.
Findings
- The primary cause of the incident was the unraveling of the release cable at the point where the cable is shared between the two release pulleys.
- The release cable had become detached from the larger link within the mechanism, preventing the mechanical linkage from functioning as intended until the physical tension change during the tow plane's descent forced a separation.
Safety action
Following the incident, the event was reviewed with all flying personnel. An inspection of the release cables on other gliders in the fleet was conducted, and no similar damage was identified. As a preventative measure, it was recommended that release cables undergo inspections every three months.