What happened
On November 11, 2012, at approximately 17:30 local time, a Robinson R-44 helicopter, registration EC-JGZ, was performing a low-altitude maneuver near Castropol, Asturias. The aircraft, operated for private use, had landed earlier that afternoon at a private estate near an industrial warehouse to conduct a flight.
As the pilot initiated a takeoff maneuver, performing a low-altitude hover to execute a 180-degree left turn, the aircraft experienced a sudden, uncommanded right yaw. The pilot reported hearing a loud noise and feeling a physical impact through the tail rotor pedals. In an attempt to stabilize the aircraft, the pilot applied flight controls and closed the fuel flow to the engine. Despite these efforts, the helicopter could not be recovered and impacted the ground, resulting in the aircraft overturning on its left side. The pilot sustained minor injuries and was the sole occupant of the aircraft.
The investigation
The CIAIAC investigation focused on the mechanical failure of the tail rotor assembly and the environmental conditions at the landing site. Investigators examined the wreckage and found significant damage to the main rotor, the power transmission, the fuselage, and the tail cone. Notably, the tail rotor drive shaft exhibited a failure due to torsional breakage.
Physical evidence at the scene included a torn polypropylene raffia sack, commonly used in construction, located between the aircraft and the warehouse wall. A witness observed the sack being lifted from a shed and moving toward the rear of the aircraft just before the instability began. Upon inspection of the tail rotor blades, investigators found polypropylene fibers embedded in the blade tips, confirming contact with the sack. The investigation also confirmed that the aircraft's maintenance program was up to date, with the most recent 50-hour inspection completed at 1,300 flight hours.
Findings
- The primary cause of the accident was the torsional breakage of the tail rotor drive shaft, which occurred due to the sudden overstress caused when the polypropylene sack became entangled in the tail rotor.
- The sack was likely sucked into the tail rotor's airflow as the pilot's leftward turn brought the tail assembly closer to the shed.
- A contributing factor was the pilot's failure to identify the sack as a potential hazard capable of being drawn into the rotor'induced airflow during low-altitude maneuvers.