Incident Overview
On 28 November 2017, at 12:00 local time, a student pilot was conducting a training flight along a route from Dęblin to Nowe Miasto, Warka, and back to Dęblin. While approaching the initial point of the route, after setting engine power to cruise range and transitioning to level flight, the pilot observed an anomaly. The power indicator on the engine power gauge changed from white to yellow, and the displayed value fluctuated between 70% and 90%. Additionally, the twist grip control exhibited non-standard indications, causing the helicopter to deviate from the established flight direction.
Actions Taken
The student pilot decided to abort the flight and return to the departure airfield. The abnormal indications persisted until landing. After landing and moving the engine power lever to the IDLE position, the power gauge readings fluctuated between 2% and 5%. Following engine shutdown and a subsequent power-on, the self-test phase displayed a throttle malfunction signal that had not been present before the flight.
Maintenance Findings
The CAMO Manager and the Maintenance Organization Manager were informed. The helicopter was withdrawn from service. A mechanic from the maintenance organization inspected the throttle position measurement system and identified a fault in the throttle position sensor. The sensor, part number HG70-2308 with serial number 125234, was replaced with a new unit, and adjustments were made in accordance with maintenance manual MM72-A-10. A ground run was performed, and during a recheck of onboard systems, no abnormalities were found. The helicopter was returned to service.
Cause
According to the investigation, the cause of the incident was a malfunction of the throttle position sensor.
Preventive Actions
The user and investigating entity briefed all AOSL flight personnel about the incident. The Polish State Commission for Aircraft Accident Investigation (PKBWL) did not issue any safety recommendations.