What happened
On April 30, 2019, a Bell 206 L3 helicopter, registration HK3312, was performing a special external load flight operation in Sabanalarga, Antioquia. The mission involved transporting 804 lb of electrical cable pulleys via a long sling from Valle de Toledo to a collection point in Sabanalarga.
During the final approach to the landing site, at an altitude between 100 and 150 feet, the aircraft encountered fluctuating wind conditions. While attempting to maintain a hover facing the wind, the helicopter experienced a sudden loss of altitude. The pilot attempted to apply power to recover, but the aircraft entered a state of power settling (vortex ring state).
To prevent the heavy load from falling on ground personnel, the pilot chose not to jettison the cargo. As the load reached the ground, the pilot attempted to transition into forward flight. This resulted in a heavy impact with the terrain, followed by a dynamic rollover to the left. The impact caused the separation of the tail cone, significant damage to the main rotor blades, and structural damage to the airframe. A small fire ignited in the engine section but was quickly extinguished by the pilot using an onboard extinguisher. The pilot was able to evacuate the aircraft uninjured.
The investigation
The GRIAA investigation examined the flight history, maintenance records, and environmental conditions at the time of the accident. Investigators verified that the aircraft was airworthy, with all documentation up to date, and that the weight and balance were within manufacturer limits. The long sling used for the operation was inspected and found to be appropriate for the 804 lb load.
Technical analysis focused on the aerodynamic state of the helicopter during the approach. The investigation reviewed video evidence from a witness and analyzed the impact dynamics. The investigators also evaluated the pilot's decision-making process, specifically the choice to retain the load despite the deteriorating flight conditions to protect personnel on the ground.
Findings
- The primary cause of the accident was a hard landing resulting from a sudden, unnoticed loss of altitude caused by the helicopter entering a power settling condition.
- Contributing factors included fluctuating wind conditions characterized by both thermal and orographic turbulence in the area.
- The pilot's decision to avoid jettisoning the load to protect ground personnel prevented immediate weight reduction but contributed to the inability to recover altitude during the descent.
- The aircraft sustained substantial structural damage, including the separation of the tail cone and the right skid.