What happened
On May 8, 1995, a Robinson R44 helicopter was conducting a flight from Kassel-Calden to Hoyerswerda. After a stop at Kamenz to refuel and pick up additional passengers, the aircraft departed Kamenz at 15:51. The flight proceeded toward the south, passing over the Dahlener Heide and following the Elbe river.
As the aircraft flew near Kreinitz at an altitude of approximately 200 meters, witnesses observed the helicopter flying at a steady altitude and normal speed. However, after passing the southernmost property in the area, witnesses heard an unusual noise. Moments later, a piece of the main rotor fell toward the ground, followed by the entire main rotor separating from the aircraft with a tilting motion. The fuselage pitched downward and crashed approximately one kilometer from the last observed position. The impact resulted in 4 fatalities, including two pilots and two passengers.
The investigation
The investigation involved the German Federal Bureau of Aircraft Accident Investigation (BFU) working alongside police, the Robinson Helicopter Company, and representatives from the NTSB and FAA. Investigators examined the wreckage in Braunschweig and compared the event to several similar accidents involving the R4/R22 series in Germany.
Technical analysis of the wreckage revealed that the aircraft experienced an extreme change in the teeter angle between the main rotor and the mast, a phenomenon known as mast bumping. This caused the rotor head to be destroyed, leading to contact between the rotor blades and the cabin, which ultimately caused the aircraft to disintegrate in flight. While the investigation could not identify the specific initiating event or a specific manufacturing defect, it noted that the R44 design has a limited ability to absorb the effects of pilot error or mechanical failure.
Findings
- The primary cause of the structural failure was mast bumping, which led to the separation of the main rotor from the mast.
- The aircraft's design characteristics provided little margin for error in the event of a mechanical or operational failure.
- The pilot on the right seat lacked specific type rating experience for the R44, though the pilot in command was fully qualified.
- There was no evidence of engine failure, weather-related issues, or bird strikes contributing to the accident.
- The takeoff weight was slightly above the maximum allowable limit, though this was not determined to be a decisive factor in the crash.