Amateur-built ROTORWAY TALON N220AF accident near Indian Lake Estates, Florida

Probable cause

A loss of helicopter control following an uncommanded increased left cyclic pressure during landing for reasons that could not be determined because postaccident examination of the helicopter revealed no evidence of any mechanical malfunctions or anomalies.

NTSB analysis

The student pilot, who was the owner and builder of the experimental amateur-built helicopter, stated that he performed some adjustments to the main rotor blade track and balance and then adjusted the slider ball adjustment collar, located in the rotor hub on the swashplate assembly, on the morning of the accident flight. After making the adjustment, the student conducted an uneventful test flight in the airport traffic pattern, and he then decided to depart on his planned cross-country flight. While approaching to land at his destination, the student felt increasing left cyclic pressure, which increased as the helicopter descended. The student stated that he did not have any further recollection of the accident. A witness reported that the helicopter rolled left about 25 ft above ground level, impacted the ground, and then came to rest on its right side.

Postaccident examination of the helicopter revealed no evidence of preexisting mechanical malfunctions or anomalies. According to the helicopter kit manufacturer, cyclic stiffness and increased cyclic pressure can be caused by worn elastomeric bearings or an incorrectly adjusted slider ball collar. However, a detailed examination of the elastomeric bearings revealed that they were within manufacturer specifications for torsional stiffness and lateral bulge. Although a postaccident hover flight test conducted by the manufacturer showed that an overtightened slider ball adjustment collar can lead to increased left cyclic pressure, postaccident measurements taken by the pilot indicated that the slider ball adjustment was also within manufacturer specifications. The reason for the increased left cyclic pressure could not be determined.

Text from the NTSB. Open the NTSB docket for ERA15LA155 for the full record.