Factual Information
On November 27, 2022, a TransHeli Co., Ltd. helicopter, model S-58JT with registration HL9678, crashed into a forest in Yangyang-gun, Gangwon-do. The accident was investigated by the Aviation and Railway Accident Investigation Board (ARAIB) under the Republic of Korea's Aviation and Railway Accident Investigation Act.
Flight History
The helicopter was on a deployment operation when it experienced a loss of tail-rotor functionality. The flight path and crash point were estimated as shown in Figure 1 of the report. The final impact site was in a forested area near 365, Eoseongjeon-ri, Hyeonbuk-myeon, Yangyang-gun.
Aircraft and Crew
The helicopter was equipped with a tail rotor drive shaft and gearbox. The pilot, mechanic, and assistant mechanic were on board. No specific details about their qualifications or experience were provided in the report. The aircraft had undergone major maintenance inspections as per its maintenance schedule.
Investigation Findings
The ARAIB conducted thorough examinations including engine teardown, fuel testing, sound spectrum analysis, and CCTV footage review. The sound spectrum study showed the helicopter entered a spinning descent before impact. The tail rotor assembly and its drive system were found to have malfunctioned, leading to a loss of anti-torque capability. The fire that occurred post-crash was investigated, and the ignition source was analyzed but not explicitly attributed to any component.
Probable Cause
The probable cause of the accident was determined to be a tail-rotor functional loss. The report stated that the helicopter crashed due to this loss of functionality. No other contributing factors were listed as per the available source material.