Incident Overview
On August 5, 2020, a Guimbal-Cabri-G2 helicopter (registration SP-NGU) operated by the Academic Aviation Training Center of the Polish Air Force Academy in Dęblin experienced an in-flight anomaly during a training flight. The flight was planned under visual flight rules (VFR) during daytime, from Nowe Miasto nad Pilicą to Dęblin.
Sequence of Events
The helicopter departed at 12:13 local time. During the climb, at approximately 900 feet above ground level, the aircraft commander observed that the helicopter began to lose directional control in a stepwise and abrupt manner. The Multi-Function Display (MLI) indicated engine power fluctuations of 20–25% relative to the set value during climb. Consequently, main rotor rpm varied between 515 and 540 and entered the yellow warning range. The governor warning light did not illuminate.
Crew Actions
The commander immediately discontinued the planned mission and informed the flight director of the situation. A safe landing was executed back at the departure airfield.
Investigation Findings
The Polish State Commission on Aircraft Accident Investigation determined that the cause of the incident was contamination of the charge pressure nozzle with a fuel-air mixture. No contributing factors were identified.
Preventive Measures
The operator proposed and implemented the following preventive actions: the incident was discussed with instructional staff, civilian and military students, and technical personnel. Particular emphasis was placed on maintaining situational awareness during flight and proper crew coordination in emergency situations. Additionally, the charge pressure nozzle was cleaned and flushed, and the ignition system spark plugs were replaced.