What happened
On 9 May 2013, at approximately 09:38 KST, an S-64E helicopter, registration HL9467, crashed into the midstream of Imha Dam in Andong-si, Gyeongsangbuk-do. The aircraft, operated by the Forest Aviation Headquarters, was performing a routine maneuver to rinse a water tank following a forest fire suppression mission.
During the approach to the water surface, the aircraft's descent rate became unmanageable, leading to a high-impact collision with the water. The crash resulted in two fatalities, involving the captain and the first officer, while the aircraft mechanic sustained serious injuries. The impact destroyed the aircraft, including the separation of the tail boom.
The investigation
The Aviation and Railway Accident Investigation Board (ARAIB) examined the wreckage, flight recorder transcripts, and pilot training records. The investigation focused on the flight crew's performance during the final approach and the environmental conditions at the site. Investigators analyzed the cockpit voice recorder (CVR) to reconstruct the sequence of events leading to the impact and reviewed the operator's Crew Resource Management (CRM) protocols and training curriculum.
Findings
- The primary cause of the accident was that the captain ignored the altitude alarm warning and misjudged the aircraft's altitude due to the glassy water effect, which delayed necessary power increases and prevented the control of the aircraft's sinking momentum.
- The crew demonstrated a significant lack of CRM skills, as the first officer failed to provide critical callouts regarding altitude, sink rate, or airspeed until the moment of impact.
- The captain exhibited poor attention to flight parameters and a failure to follow standard checklists, evidenced by taking off with the auxiliary fuel pump inactive.
- The crew was not wearing life vests during the operation, and the operator's regulations did not specifically mandate survival equipment for inland water operations.
- The operator's training curriculum lacked instruction on the specific risks associated with the glassy water effect.
Safety action
- The ARAIB recommended that the Civil Aviation Office reinforce regulations to require life vests for all crew members performing operations over inland waters.
- Recommendations were made to the Forest Aviation Headquarters to improve pilot training and evaluation systems, specifically to include recurrent training and instruction on the glassy water effect.
- The operator was advised to strengthen CRM procedures and clearly define the roles of the Pilot Flying (PF) and Pilot Monitoring (PM).
- Local emergency management agencies were advised to establish specialized life-saving systems tailored to the specific depths and conditions of freshwater lakes within their jurisdiction.