What happened
On 3 August 2009, an unmanned rotorcraft, an RMAX L17 with registration S7044, was being operated for agricultural spraying in a rice paddy in Imsil-gun, Jeollabuk-do, Republic of Korea. The aircraft was being operated by the Osu Agricultural Cooperative.
Following a hovering takeoff, the aircraft began moving backward toward the pilot. The pilot attempted to intervene with control inputs to stop the rearward drift, but the movement could not be arrested. The rotorcraft traveled approximately 18 meters backward over a period of six seconds, striking the pilot and subsequently crashing into the terrain. The collision resulted in one fatality.
The investigation
The investigation conducted by the ARAIB examined the flight data recorder, the radio control box, and the aircraft's mechanical condition. Investigators analyzed the pre-flight procedures, the design of the control interface, and the safety protocols of the aerial spray team. The examination of the radio control box and flight data revealed that the aircraft's systems and the radio control box were functioning normally at the time of the accident, and no external mechanical failures were identified.
Findings
- The pitch trim switch was improperly set to the "pitch up 3 unit" position prior to takeoff and this error was not detected during pre-flight checks.
- The design of the trim switches, which feature a convex surface, made them susceptible to unintentional changes through careless handling or contact with objects.
- The pilot's safety distance of 15 meters from the aircraft was insufficient to protect against abnormal movement.
- The operator's safety regulations and supervision were inadequate, and the pilot's training program lacked a human error prevention component and a method for maintaining proficiency.
- The pre-flight checklist was difficult to use in its booklet format and did not specifically require a check of the trim switch positions.