What happened
On November 7, 2019, a Bell 206 L3 helicopter, registration HK3978, was performing a non-scheduled cargo/transport flight involving the transport of valuables. The flight, operated by Delta Helicópteros, S.A.S., originated from Popayán, Colombia, and had completed a multi-stop itinerary through several towns before returning to the Guillermo León Valencia Airport.
As the pilot was executing a short final approach to the helicopter spot on the commercial apron, the aircraft experienced a violent impact and intense vibrations. The pilot reported that the collective control became unresponsive, leaving the aircraft in a fixed climbing attitude. To manage the emergency, the pilot transitioned the aircraft into an autorotation and moved toward a safety area. This maneuver resulted in a hard landing, during which the main rotor struck the stabilizer, causing substantial damage to the airframe, including a bent right skid and a fractured stabilizer vane.
All three occupants (the pilot and two passengers) evacuated the aircraft safely and sustained no injuries.
The investigation
The GRIAA investigation focused on the mechanical failure of the transmission assembly. Investigators examined the transmission support arms and identified that the right rear link had fractured. Laboratory analysis of the components revealed that the fracture was not caused by the impact of the landing itself, but rather by a prior degradation of the elastomeric components.
Technical inspections of the mounting assembly showed mechanical wear and metal-to-metal contact between the wedges and the internal/external metallic members. This wear exceeded the manufacturer's allowable limits. The investigation also scrutinized the maintenance history of the transmission support arms, specifically the vulcanization process used on the elastomeric rings.
Findings
- The primary cause of the accident was the fracture of the right rear link of the transmission assembly. This failure caused the transmission to shift, which rendered the flight controls unresponsive and forced the pilot into an emergency autorotation.
- The fracture originated from an improper repair of the elastomeric components. The operator had utilized a non-aviation workshop to perform vulcanization on the transmission support arms using unauthorized rubber compounds and methods that did not meet manufacturer specifications.
- This substandard repair led to rapid degradation of the elastomeric bearings, resulting in excessive vibrations and metal-to-metal contact within the assembly.
- A contributing factor was the use of unauthorized maintenance practices by the operator, specifically the outsourcing of critical component repairs to uncertified facilities not recognized by the manufacturer or the Civil Aviation Authority.
Safety action
- The investigation issued a recommendation to Delta Helicópteros, S.A.S. to review its maintenance programs and processes to ensure all repairs and substitutions are performed only by authorized, certified workshops and qualified personnel.
- A recommendation was also made to the Aeronáutica Civil de Colombia to disseminate the findings of this report to helicopter operators to improve Safety Management Systems (SMS).