Incident Details
On 17 November 2015 at 12:00 LMT, a Guimbal Cabri G2 helicopter was conducting training flights under exercise IV/17, performing circuits simulating autorotation. The crew noted three instances of momentary power loss. The first two occurred before the second turn at an altitude of 1100 ft and were lightly perceptible, initially attributed to turbulence. The third instance occurred during takeoff at an altitude of 20-30 ft in the initial acceleration phase, where the crew felt a brief but very strong dynamic jolt associated with the momentary power loss. The crew discontinued the task and landed at the departure airport.
Response and Investigation
The maintenance station Heli Invest Services was informed. The helicopter was withdrawn from further operation. The Helicopter Integrated Safety Management (HIS) CAMO recommended inspecting the engine power management system, and following analysis, a decision was made to replace the tachometric breaker with a new one. After replacement, a test flight was conducted; no abnormalities were found in flight or during post-flight system checks.
The manufacturer was contacted for an opinion. The manufacturer confirmed that a likely cause of the disturbances in the governor system operation could be a temporary incorrect operation of the tachometric breaker. The helicopter was returned to service.
Probable Cause
The probable cause of the incident was the incorrect operation of the tachometric breaker.
Safety Recommendations
No safety recommendations were formulated by the commission.