What happened
On 13 October 2021, a Robinson 22 Beta II helicopter, registration ZS-RNH, was performing hover training exercises at the threshold of Runway 35 at Port Elizabeth International Airport. The flight, which was part of a Part 141 training program, included a student pilot and a flight instructor.
During the session, the instructor took control of the aircraft to reposition it for a better takeoff wind. Once the helicopter reached a stable hover in ground effect, the instructor handed control back to the student. Shortly after, the instructor observed a decrease in engine revolutions per minute (RPM). Despite the instructor's attempts to adjust the throttle to stabilize the engine, a low RPM warning was triggered, and the aircraft began to sink. To prevent a harder impact, the instructor raised the collective to cushion the descent. The helicopter landed safely with no injuries and no damage to the aircraft.
The investigation
Following the incident, investigators examined the mechanical condition of the engine controls. A post-incident inspection by engineers revealed that an insert housing a ball within the rod end of the overtravel spring had become loose and had separated from the rod end.
Records indicated that while a collective overtravel spring had been replaced during a previous maintenance inspection, there was no recent work performed on the specific rod end that failed. The aircraft's logs showed that the failed rod end was an original Robinson part that had been in service since November 2008. Although the part was not life-limited and was subject to on-condition monitoring, the separation of the insert led to the loss of engine power.
Findings
- The primary cause of the engine power loss was a loose insert within the rod end of the throttle control overtravel spring.
- The instructor was properly licensed for the training flight at the time of the occurrence.
- The aircraft was able to land without structural damage due to the instructor's corrective actions with the collective.