What happened
On April 18, 2015, a Robinson R44 Raven II was conducting a tourist flight from Serock toward the EPBC aerodrome. Approximately five minutes into the flight, the pilot observed erratic engine RPM fluctuations on the instrument display. The readings fluctuated between 100% and 104%, then 99% and 108%, eventually reaching a peak of 115% before dropping to 97%.
To prevent potential engine damage caused by the rising RPM, the pilot manually reduced the throttle. Shortly thereafter, a low main rotor RPM warning signal activated. In response to these indications, the pilot decided to terminate the flight and perform a precautionary landing in an open field. The pilot executed a 180-degree left turn into the wind and successfully landed the aircraft in a clear area away from obstacles. There were no injuries to the occupants during the landing.
The investigation
The investigation focused on the mechanical stability of the engine and the impact of environmental conditions. Following the incident, the aircraft was transported by road to a maintenance organization. In consultation with the Robinson Helicopter Company, several inspections and overhauls were performed. The investigation established that the magneto units required major repair, and both the governor and its controller were replaced. Following these repairs and standard scheduled maintenance, the aircraft was returned to service.
Findings
- The primary cause of the engine governor malfunction was likely attributed to faulty operation of the controller unit.
- Contributing factors included a malfunction in the left magneto and/or the influence of strong rear-quarter winds, which were blowing from approximately 340 degrees at 16 knots with gusts up to 26 knots.