Accident Summary
On 7 November 2019, at approximately 15:55 local time (20:55 UTC), a Bell 206 L3 helicopter, registration HK3978, operated by Delta Helicópteros S.A.S., sustained a hard landing at Guillermo León Valencia Airport in Popayán, Cauca, Colombia. The aircraft was conducting a non-regular air taxi flight transporting valuables with two escort passengers. The pilot and both passengers evacuated unharmed.
Flight History
The helicopter departed Popayán at 09:10 local time and followed an itinerary that included Argelia, Balboa, Magüí Payán, Barbacoas, and Policarpa before returning to Popayán. While approaching the airport, air traffic control cleared the pilot to proceed via the parallel of runway 08 directly to the commercial platform helicopter spot, as another aircraft was taxiing on the runway.
Sequence of Events
During the short final approach, the pilot perceived a strong impact inside the helicopter followed by vibration. Attempting to land, the pilot found the collective control unresponsive. The pilot then moved the aircraft toward the safety area, reduced throttle to minimum RPM, and entered autorotation. A hard landing ensued, during which the main rotor struck the stabilizer, and other substantial damage occurred.
Damage
The helicopter sustained substantial damage: bending of the right skid, fracture of the elevator trim tab, fracture of the left rear transmission arm, and sudden stoppage of the engine.
Investigation
The Colombian Accident Investigation Authority (GRIAA) investigated. The investigation determined that the hard landing resulted from a fracture of the right rear link of the transmission assembly. This fracture was caused by improper repair of all elastomeric components. The fracture allowed the transmission to shift, locking the collective control in a forward position, which forced an autorotation and subsequent hard landing. A contributory factor was the operator's practice of contracting vulcanizing work for the elastomeric components of the transmission support links to non-aeronautical workshops not authorized by the manufacturer or the civil aviation authority.
Probable Cause
The probable cause was the fracture of the right rear link of the transmission assembly, originating from improper repair of all elastomeric components.