Accident Overview
On 16 January 2019, at 11:29 local time, a Robinson R44 Raven I helicopter, registration HB-ZDW, experienced an engine failure shortly after departing from Luzern Beromünster Airport (LSZO). The helicopter was on a private VFR flight with one pilot and three passengers. During the initial climb, the pilot perceived a sudden left yaw, followed by a low rotor RPM warning. The pilot immediately lowered the collective and initiated an autorotation, turning back towards the airfield.
Flight History
After routine pre-flight preparations, the pilot started the engine and allowed it to warm up with carburetor heat fully open. A hover check revealed no anomalies. At 11:26, the pilot began the takeoff on runway 33. During the climb check, the pilot again fully opened the carburetor heat to compensate for reduced heating when pulling collective. The helicopter reached about 2800 ft MSL (650 ft above aerodrome elevation) and 70 kt when the engine failed. The pilot autorotated back to the airfield, touching down approximately 100 meters past the threshold of the glider runway 33. The left skid sank into soft ground, causing the helicopter to rotate 90 degrees left, tip over onto its right side, and come to rest on its side. All occupants exited unaided and uninjured. The helicopter was substantially damaged.
Technical Findings
Post-accident examination found no pre-existing malfunctions that could have caused the engine failure. The fuel system functioned correctly, and no water or contamination was detected. Laboratory analysis of fuel showed a mixture of AVGAS 100LL with a small amount of unleaded automotive gasoline, within allowable limits. The engine was test-run and operated within normal parameters. The ignition switch showed high wear but remained functional; wiring was intact. The investigation could not determine the cause of the engine failure. Carburetor icing was considered unlikely because carburetor heat had been fully applied.
Outcome
The pilot successfully performed an autorotation and returned to the airport, but the helicopter tipped over during the landing roll due to soft ground. The cause of the engine failure remains undetermined.