Accident Summary
On November 7, 2017, at about 0930 central standard time, a Bell 206B helicopter (N93PH) was substantially damaged in an accident near Rolling Fork, Mississippi. The pilot, who sustained minor injuries, was conducting an aerial application flight under 14 CFR Part 137.
Pilot Account
The pilot reported that while spraying a river, he felt an abrupt right yaw followed by a left yaw. He raised the helicopter's nose to the right to clear a line of trees parallel to the river. Upon reaching treetop level, he realized the airspeed was low and initiated an autorotation by lowering the collective. He pulled full collective as the skids contacted the ground hard, and the helicopter came to rest on its right side.
Damage Examination
Postaccident examination revealed the tailboom had fracture separated, consistent with main rotor blade contact. Both main rotor blades showed impact damage and warping with slight spanwise deflection opposite the direction of rotation. One blade had a chordwise crack in the center section. Multiple drive train fractures were found, but flight continuity was established. The tail rotor hub and blades remained attached to the gearbox; one blade was intact, and the other was broken chordwise at the doubler. The tail rotor hub rotated freely by hand.
Engine and Systems Findings
The engine examination showed the transmission rotated freely without binding, and chip detectors were clear. The main transmission input shaft was fracture separated with circumferential scraping near the firewall opening. Metallurgical analysis of the compressor found no fatigue on blade fracture surfaces. The 1st-stage compressor inlet and blades had damage consistent with foreign object ingestion, and the case halves were pierced in several areas. N1 and N2 rotated freely. The 4th- and 1st-stage turbine wheels were undamaged. Black sludge-like debris, identified as an aluminum alloy not used in engine components, was found along the gas path, concentrated on the inner surface of the outer combustion case. Fuel was present in the lines and filters; the fuel control inlet strainer had no contaminants. The bleed valve was open and coated with the sludge. The fuel control unit and power turbine governor were functionally tested and found slightly outside manufacturer specifications.
Postaccident examination of the airframe, engine, and fuel system found no evidence of preaccident mechanical malfunctions or failures that would have precluded normal operation.