What happened
On August 18, 2012, a Bell 206L3 helicopter, registration HK-4871, was conducting an external cargo operation near Buriticá, Antioquia, Colombia. The aircraft, operated by HELIFLY, was performing sling-load tasks for a mining company, transporting loads between an extraction site at 3,0-00ft and a delivery site at 6,300ft. Because the extraction area prevented landing, ground personnel were responsible for attaching loads to the helicopter's cargo hook.
During the afternoon operations, the pilot was transporting a cargo bag attached to the hook. Inside this bag, a lightweight plastic tarp had been placed by ground personnel. While flying at approximately 30 KIAS, the wind caught the plastic tarp, causing it to inflate like a parachute. This movement shifted the cargo bag backward, causing it to strike the tail rotor assembly.
The impact was severe enough to tear the tail rotor gearbox and its associated components away from the tail boom. The pilot immediately initiated an emergency autorotation. During the descent, the pilot had to maneuver to avoid power lines, eventually impacting trees before the aircraft reached the ground. The pilot was able to evacuate the aircraft unharmed.
The investigation
The GRIAA investigation focused on the mechanical failure of the tail rotor and the sequence of the external load movement. Investigators examined the wreckage, finding that the tail rotor gearbox had been completely detached and was located approximately 120 meters behind the main fuselage. The investigation also reviewed the aircraft's maintenance records, which showed the Bell 206L3 was up to date with all required inspections and manufacturer bulletins.
Investigators also analyzed the human factors and operational procedures. While the pilot was fully qualified and medically fit, the investigation identified a lack of coordination between the flight crew and the ground personnel regarding the contents of the cargo bag. The presence of the low-density plastic tarp created an unpredictable aerodynamic effect that the pilot could not have anticipated.