Incident Overview
A helicopter experienced an anomaly during takeoff from a heliport located atop a 10-story parking structure. As the aircraft transitioned to forward flight, the pilot reported hearing a "loud pop or snapping sound" and subsequently felt a main rotor imbalance and vibration. The pilot elected to return to the heliport and executed a landing on the skids. However, after touchdown, the helicopter rolled over and came to rest on its left side.
Examination Findings
Post-accident examination revealed that the skid cross tubes had been displaced approximately 2 inches to the right in their fuselage attachment bushings. The main rotor transmission was inclined approximately 20 degrees to the right and 10 degrees forward. Inspection and testing of the hydraulic pump, three flight control servos, and two hydraulic filters found no anomalies. The tip of one main rotor blade and a portion of one pitch change link were not located after the accident. The mating end of the recovered pitch change link exhibited bending along its length and crippling at the separation point, consistent with an overload failure.
Conclusion
The investigation did not determine a probable cause for the event. The damage observed indicates a structural failure, but the initiating sequence remains unknown.