What happened
On August 28, 2014, a Robinson R22 Beta helicopter, registration HK4287G, was conducting a flight training mission departing from Medellín's Enrique Olaya Herrera Airport. During the return flight, the pilot initially landed at a secondary location due to deteriorating weather, noting slight vibrations and a left yaw. After maintenance personnel addressed the issue and weather improved, the crew resumed the flight toward Medellín.
During this subsequent leg, the aircraft experienced abnormal vibrations, a left yaw, and a partial loss of engine power accompanied by a drop in rotor RPM. The pilot executed an emergency autorotation into an unprepared field near Amagá. Due to the steep 35.7° slope of the terrain, the aircraft underwent a dynamic rollover upon impact. The impact caused significant structural damage, including a fractured tail boom, deformed main rotor blades, and damage to the tail rotor and drive shaft. The pilot and technician were able to evacuate the aircraft uninjured, and no fire occurred.
The investigation
The GRIAA investigation focused on the engine performance and maintenance history. The Lycoming O360J2A engine was sent to the manufacturer in the United States for functional testing. While the engine passed most operational tests, investigators found that three upper spark plugs showed abnormal physical conditions, specifically electrode wear and oil contamination.
Maintenance records revealed that a major engine overhaul had been completed shortly before the incident. Although spark plugs had been replaced on the day of the accident as a corrective measure for earlier vibrations, the investigation identified that the newly installed components were in deficient physical condition, featuring worn electrodes.