What happened
On 6 February 2012, a SW-4 helicopter, registration HL9403, operated by Yechon Astro-Space Center, Inc., was conducting a forest fire prevention patrol in the Dalseong-gun area of Daegu-si. While flying at an altitude of approximately 150 to 200 feet AGL, the aircraft experienced an in-flight engine shutdown.
As the engine power decreased, the pilot observed the aircraft yawing to the right and heard warning horns and engine noise changes. The pilot attempted an emergency auto-rotation landing. During the maneuver, the pilot attempted to avoid high-voltage power lines by pulling back on the cyclic, which caused the aircraft to lose pitch control and increase its sink rate. The helicopter subsequently performed a hard landing in a frozen paddy field, resulting in the destruction of the aircraft and one serious injury to the pilot.
The investigation
The ARAIB investigation focused on the fuel management practices of the operator and the mechanical state of the aircraft. Investigators examined the fuel system, including the fuel quantity indicator and sensors, and reviewed the maintenance and training records of the Yechman Astro-Space Center. The investigation also looked into the pilot's training curriculum and the company's refueling procedures.
Findings
- The primary cause of the accident was the depletion of fuel following an inaccurate refueling process. The operator relied solely on a malfunctioning fuel quantity indicator to determine the amount of fuel loaded, which resulted in significantly less fuel being supplied than intended.
- The pilot failed to recognize the illumination of the low fuel warning light and the master caution light during the flight.
- During the auto-rotation attempt, the pilot failed to jettison the Bambi bucket and was unable to adequately manage the sink rate after attempting to clear power lines.
- The operator's refueling procedures lacked a secondary method of visual verification for the actual fuel quantity.
- The company's training program for the pilot was insufficient, featuring improper instructor appointments and the replacement of essential emergency procedure training with self-study.
Safety action
- The ARAIB recommended that the manufacturer, PZL SWIDNIK S.A., consider increasing the inspection frequency for the fuel quantity indicator and sensor on SW-4 aircraft.
- Recommendations were made to the regional aviation administration to enhance supervision of pilot training programs and compliance with operational regulations.
- The operator was advised to implement visual verification during refueling and to ensure that all pilots strictly adhere to low-fuel warning procedures.