Incident Overview
On 17 May 2011, a Hélicoptères Guimbal Cabri G2 helicopter (serial number 1016) departed from Frankfurt-Egelsbach for a scenic flight. During a maneuver involving reduced load factor, the engine failed at approximately 1,500 ft AMSL. The pilot initiated an autorotation and successfully restarted the engine at 500 ft above ground level before returning to the departure airfield. No injuries or damage to the aircraft were reported.
Aircraft and Pilot Details
The two-seat helicopter was powered by a Lycoming O-360-J2A piston engine and featured an Avstar MA-4SPA carburetor. The 35-year-old pilot held a commercial helicopter license with type ratings for several models, including the Cabri G2. He had a total of 1,587 flight hours, with 118 on this specific model.
Investigation Findings
Following the incident, the operator and manufacturer conducted extensive troubleshooting. Multiple test flights resulted in repeated engine failures during "push over" maneuvers. The original carburetor (No. 1) was found to leak when the electric fuel pump was engaged at ground level. Subsequent analysis by the carburetor manufacturer revealed that both Carburetor No. 1 and a replacement unit (No. 2) suffered from defects in the needle, seat, or float holder areas. These issues caused excessive friction and restricted float movement, leading to fuel overflow at higher pressures.
Safety Recommendations
The helicopter manufacturer noted that the maneuvers performed were outside the normal safe flight envelope defined in the flight manual. They emphasized that such aggressive "push over" actions are dangerous and strictly prohibited for many helicopter types. Consequently, a sequence of aggressive push-over maneuvers was added to the standard test flight program to better detect such fuel system vulnerabilities.