What happened
On October 10, 1999, an Air Corps SA316B Alouette III was conducting a Search and Rescue (SAR) mission near Ardmore Head, County Waterford. The mission involved recovering an injured woman who had fallen down a cliff. The aircraft approached the cliff face to deploy a winchman at an altitude of approximately 80 feet. During this phase, the helicopter's rotor downwash lifted a foil thermal blanket covering the casualty.
The aircraft commander noticed the blanket, but because the winchman was already on the cable, maneuvering to avoid the object was not feasible. Shortly after, the crew experienced a loud bang, intense vibrations, and a significant loss of lift. The pilot attempted to arrest the descent using full collective power, but the aircraft continued to drop toward the sea. Fearing an imminent ditching, the pilot prepared the flotation gear. The aircraft eventually regained power and leveled out at 40 feet. After the winchman was safely recovered, the crew inspected the aircraft and found no significant damage. The mission was subsequently completed, and the patient was successfully transferred to Cork Regional Hospital.
The investigation
The investigation established that the thermal blanket became temporarily entangled in the main rotor system. This entanglement disrupted the airflow through the blades, leading to the observed vibration and loss of lift. The investigation concluded that the blanket eventually tore away from the rotor, which allowed the aircraft to regain sufficient power to maintain flight. The clicking noise heard by the crew was attributed to small shreds of the blanket remaining attached to the blades.
Findings
- The primary cause of the loss of lift was the entanglement of a lightweight thermal blanket in the main rotor.
- The presence of approximately 50 spectators and various rescue personnel on the cliff-top obscured the crew's ability to visually assess the area before the approach.
- The rotor downwash was powerful enough to lift unsecured lightweight items from the casualty site.
Safety action
Following the incident, safety recommendations were issued to the Irish Marine Search and Rescue Committee (IMSARC) regarding:
- The need to review training for ground-based rescue personnel to ensure they understand the hazards of helicopter downwash and the importance of securing lightweight items.
- The necessity of improving command and control at rescue sites to manage non-essential personnel and ensure the flight crew can clearly evaluate the landing or hoisting area.