Incident Details
On 18 April 2015, a Robinson R44 Raven II helicopter was performing a flight from Serock to EPBC airfield. Approximately five minutes into the flight, the pilot observed fluctuations in the engine RPM indicator: rises to 104% followed by drops to 100%, rises to 108% followed by drops to 99%, and rises to 115% followed by drops to 97%. After the engine RPM reached 115%, the pilot manually reduced the throttle using the throttle control handle to prevent further overspeeding and potential engine damage. Shortly thereafter, a low rotor RPM warning activated. The flight was conducted at an altitude of approximately 800 ft AGL with a tailwind and crosswind from approximately 340° at 16 knots, gusting to 26 knots.
Pilot Actions
In response to the warning, the pilot decided to abort the flight and perform a precautionary landing in an open field. The pilot selected a suitable landing area, executed a left turn of approximately 180° into the wind, and safely touched down away from obstacles. The landing was completed without consequences. During the landing, the engine RPM began to stabilize, and after touchdown, no deviations from normal operation were observed. The helicopter was shut down according to the procedures in the flight manual. After the main rotor stopped, the pilot and passengers safely exited the helicopter.
Investigation and Maintenance
The helicopter was secured by technical personnel and transported by ground to a maintenance organization. Following consultations with the manufacturer, Robinson Helicopter Company, recommended inspections and checks were performed. The magnetos underwent overhaul, and the governor and its controller were replaced. The removed components were sent to the manufacturer for analysis. After completing these actions and scheduled maintenance, the helicopter was cleared for further operation.
Probable Causes
The Polish State Commission for Aircraft Accident Investigation stated that the causes of the engine speed governor system disturbance could have been: defective operation of the controller assembly, malfunction of the left magneto, and/or the effect of strong tail-side wind.