Bell 407 N11SP accident near Bath, New York

Probable cause

The pilot's improper recovery from an in-flight upset, which resulted in the main rotor striking and separating the tail boom. Contributing to the accident was the helicopter manufacturer's failure to warn pilots of unanticipated and unequal aft cyclic pressure in the single-pilot configured helicopter compared to the dual-pilot configured helicopter, which resulted in the in-flight upset when the pilot momentarily let go of the cyclic control.

NTSB analysis

The pilot stated that the accident helicopter was configured for single-pilot operation (the copilot controls had been removed for the assigned mission). While in cruise flight between 110 and 120 knots and about 2,500 feet mean sea level, the helicopter began pitching up and yawing right, because the force trim was the "off" position, which rendered the altitude hold feature inoperative, and the pilot responded by pushing the cyclic forward and left. The helicopter then pitched "severely" nose down and entered a right spin. At that time, the pilot saw a portion of the tail boom, tail rotor, and tail rotor gearbox falling away separately from the helicopter. The pilot entered an autorotation and landed in wooded terrain.

About 1 year after the accident, another pilot for the operator performed a maintenance test flight in a similarly configured make and model helicopter. While in cruise flight and with the force trim in the "off" position, the pilot released the cyclic momentarily, and the helicopter pitched up and rolled right. The flight scenario was duplicated several times with the copilot controls installed on the helicopter and, when the pilot released the cyclic, it maintained its same relative position, even with the force trim in the "off" position. Therefore, it appears that aerodynamic forces drove the cyclic aft in the single-pilot configured helicopter because the added weight and lever arm in a dual-pilot configured helicopter was not available to neutralize the forces. The manufacturer should have known about this characteristic of the helicopter and warned pilots of unanticipated and unequal aft cyclic pressure in the single-pilot configured helicopter compared to the dual-pilot configured helicopter. Detailed examination and testing of the helicopter and its components revealed no preaccident anomalies and no evidence of foreign object damage.

Text from the NTSB. Open the NTSB docket for ERA12TA538 for the full record.