What happened
On May 30, 2021, a Cicaré CH12 helicopter, registration LV-X774, was conducting a general aviation ferry flight from Añatuya to La Ramada. During the cruise phase of the flight, approximately 30 minutes after departure, the pilot experienced a significant increase in vibrations. Shortly thereafter, the aircraft suffered a total loss of control and plummeted to the ground in Lugones, Santiago del Estero. The impact resulted in the destruction of the aircraft and caused one minor injury to the pilot. There were no passengers on board.
The investigation
The Argentine Transportation Safety Board (JST) examined the wreckage and the circumstances surrounding the flight. Investigators noted that the pilot had experienced abnormal vibrations during the final 20 minutes of the flight. The investigation focused on the structural integrity of the tail rotor assembly and the regulatory status of the aircraft, which was operating under a special airworthiness certificate for amateur-built experimental aircraft.
Technical analysis of the wreckage revealed that the tail rotor blades had fractured, and the tail rotor assembly had physically separated from the tail boom. The investigation also looked into a previous incident involving the same aircraft on May 2/29, 2021, where a fuel line failure had caused an engine shutdown, an event that had not been reported to the JST.
Findings
- The primary cause of the accident was the catastrophic separation of the tail rotor from the tail boom, which rendered the helicopter uncontrollable.
- The failure was preceded by intense vibrations, which likely originated from a component malfunction or a pre-existing crack in a tail rotor blade identified by maintenance personnel the previous day.
- Mechanical analysis of the flange fragments indicated they had been subjected to a rapid, extreme overload.
- The aircraft's flight manual lacked specific procedures or guidance for pilots to manage or mitigate abnormal vibration levels.
- There was a discrepancy regarding the aircraft's classification; while registered as an amateur-built experimental aircraft, the investigation found the owner's involvement in the actual construction was minimal.
Safety action
- The JST recommended that the National Civil Aviation Administration (ANAC) update regulations regarding the definition and construction requirements for amateur-built experimental aircraft to ensure they align with actual industry practices.
- A recommendation was issued to Cicaré S.A. to update the CH12 pilot's flight manual to include specific procedures for managing abnormal vibration events.