What happened
On August 5, 2020, a Guimbal Cabri G2 helicopter, registration SP-NGU, was conducting a scheduled VFR daytime training flight from Nowe Miasto nad Pilicą to Dęblin. The aircraft was operated by the Academic Flight Training Center LAW in Dęblin.
During the climb phase, at an altitude of approximately 900 ft, the pilot noticed that the helicopter began to experience sudden and violent directional instability. Simultaneously, the engine power indications on the MLI display fluctuated by 20-25% relative to the established settings. These fluctuations caused the main rotor RPM to oscillate between 515 and 540, entering the yellow warning range. Although the rotor speed was unstable, the "Governor" warning light did not illuminate. The pilot immediately aborted the mission, notified flight operations, and performed a safe landing back at the departure airfield.
The investigation
The PKBWL examined the incident following the final report submitted by the aircraft operator. The investigation focused on the cause of the engine power instability and the erratic rotor RPM behavior observed during the climb.
Findings
- The primary cause of the incident was the contamination of the charging pressure nozzle with a fuel-air mixture.
- There were no contributing circumstances identified in this occurrence.