What happened
On the night of 19 February 2022, an Agusta 119 helicopter, registration ZT-RZS, was preparing for a commercial air ambulance flight from the Paarl Provincial Hospital rooftop helistop to Cape Town International Airport. During the engine start-up sequence, as the engine power reached 100% main rotor speed, the aircraft suddenly experienced a violent 9-degree yaw to the left.
This initial movement was followed by two additional full 360-degree rotations to the left. The pilot attempted to correct the motion by applying full right pedal input, but the aircraft continued to spin. During the instability, the two paramedics on board chose to jump from the aircraft while it was momentarily stationary. A third rotation occurred shortly thereafter. To stop the uncontrolled movement, the pilot closed the throttle to ground idle and subsequently shut down the engine. During the incident, one paramedic sustained minor injuries after being dragged by the helicopter skids while disembarking.
The investigation
SACAA AIID investigators examined the aircraft's mechanical systems and the pilot's actions. The investigation focused on the possibility of a tail rotor failure or hydraulic issue. Post-incident inspections of the hydraulic system, including filters and indicator pins, showed no blockages or debris. The maintenance organization (AMO) conducted extensive testing on the tail rotor servo actuator, both locally and at the manufacturer's facility, but was unable to replicate the failure or identify any anomalies.
Findings
- The pilot was well-rested and had no known stressors prior to the flight.
- The aircraft's maintenance records showed a valid certificate of airworthiness and a recent successful inspection.
- The pilot noted that the aircraft's rotation felt as though the tail rotor was locked in a specific position, and upon engine shutdown, the right-hand pedal was found fully engaged to the right.
- The cause of the uncontrolled leftward yaw could not be determined because the servo actuator could not be tested for the specific failure after being reinstalled and bench-tested.
- The paramedics disembarked the aircraft without notifying the pilot of their intention to jump.