What happened
On November 15, 2017, at approximately 10:00 local time, an MI-8MTV-1 helicopter, registration HK3908, was performing a specialized external cargo transport flight in Antioquia, Colombia. The aircraft, operated by Vertical de Aviación S.A.S, was transporting approximately 2,882 kg of steel structures intended for electrical tower construction. The flight was traveling from Tarazá toward a destination in Valdivia.
During the cruise phase of the flight at 3,500 feet MSL, the left sling of the nylon sling assembly failed near the eye. This failure caused the helicopter to tilt sharply to the right. The resulting pendulum effect caused the heavy steel load to shift and slip from the remaining right sling attachment. The cargo, consisting of roughly 40 steel angles, fell at a steep angle of approximately 55 degrees into the Vereda Piedras area. The impact struck eight houses, resulting in one serious injury to a person on the ground and causing damage to several dwellings. The crew successfully controlled the aircraft and returned to the departure site without injury or damage to the helicopter.
The investigation
The GRIAA investigation focused on the integrity of the lifting equipment and the cargo securing procedures. Investigators examined the nylon sling (part number EB3-904), which had been installed on the day of the accident. The investigation also reviewed the flight crew's credentials, the aircraft's maintenance records, and the company's risk management protocols.
Physical inspection of the wreckage revealed that while the cargo hook remained intact, the left sling arm had failed at the eye, and the right sling arm showed partial tearing approximately 40 cm from its eye. The investigation also reviewed the ground handling procedures used to prepare the load using a choker hitch method.