Accident Overview
On March 5, 2019, at approximately 1110 eastern standard time, an MD Helicopters 369D helicopter, registration N89ZC, was substantially damaged when it crashed near Talking Rock, Georgia. The commercial pilot, who was the sole occupant, sustained fatal injuries. The helicopter was being operated under 14 Code of Federal Regulations Part 133 for external load operations, specifically using a 10-bladed aerial saw to trim trees along power lines.
Flight and Witness Account
The pilot was conducting three passes to trim the full height of the trees: an upper, middle, and lower pass. A witness reported that after completing the upper pass, the pilot returned for the middle pass. During this pass, the helicopter began to rotate counterclockwise around the main rotor mast. It completed one full rotation, and during the second rotation, the helicopter struck trees and then the ground. The helicopter came to rest on its right side, sustaining substantial damage to the fuselage and tailboom.
Aircraft and Maintenance Information
The helicopter was equipped with a main rotor system consisting of five blades that turned counterclockwise when viewed from above. The most recent 100-hour and 300-hour inspections were performed on February 18, 2019, at an aircraft total time of 13,637.0 hours (2,349.0 hours Hobbs time). The Hobbs meter indicated 2,382.3 hours at the accident site.
Maintenance records revealed that the overrunning clutch subassembly had been repaired before installation on the accident helicopter, including the installation of a new outer race. This subassembly was installed during the most recent inspection. According to the logbooks, engine mounts were inspected during every 100-hour inspection per manufacturer guidance. Entries for the six previous 100-hour inspections (July 2018 through February 2019) contained no mention of defects or discrepancies with the engine mounts. The installation date of the engine mounts could not be determined. The maintenance manual included instructions for inspecting engine mounts for cracks and play, as well as visual and magnetic particle inspections for suspect assemblies.
Wreckage and Impact Examination
The helicopter impacted terrain at an elevation of 1,250 feet mean sea level and came to rest on a heading of 037°. Multiple tree strikes were observed, with the initial tree strike occurring approximately 25 feet from the ground impact. All major components remained attached to the airframe.
Flight control continuity was confirmed from the cockpit controls to the main and tail rotors. The collective control was found in the maximum (full up) position. The throttle and engine control linkages were continuous. The electric N2 trim and cyclic trim operated when power was applied. The fuel tank contained fuel.
The main rotor transmission fluid level was full. The engine-to-transmission driveshaft rotated by hand with corresponding main rotor movement. Flex frames on the driveshaft couplings were intact. Tail rotor driveshaft continuity was verified, and flex couplings remained attached with unbroken torque stripes.
All main rotor blades remained intact with impact damage consistent with unpowered rotation. The tail rotor transmission assembly remained attached; both tail rotor blades had chordwise scratching, and one leading edge was impact damaged. The tail rotor driveshaft and control push-pull tube were bent. The tailboom was fractured about 4 feet aft of the fuselage. The tail rotor driveshaft showed minor rotational scoring, and the pitch control links were intact. Oil was present in the tail rotor gear box.
An inspection panel was removed to access the engine. The compressor impeller and N1 turbine did not rotate, but the drive gear connected to the overrunning clutch could be rotated by hand. The starter generator rotated by hand. The combustion can was removed, and the first stage nozzle showed no thermal distress or damage. Chip detectors had no debris. The compressor module, governor drive shaft, and fuel control drive rotated freely. The power turbine-to-pinion gear (N2) rotated freely. Continuity of the gas producer turbine-to-compressor (N1) drive train was confirmed. No engine anomalies were found that would have precluded normal operation.
The overrunning clutch housing was fractured at its attachment flange, which remained attached to the engine gearbox. Residual oil was found when the clutch was removed. Rotational scoring was present on the upper bearing support. The upper bearing contained grease. The overrunning clutch operated as designed when rotated in reverse. The outer race exhibited a torsional fracture on the shaft adjacent to the splines. The C-clip retained tension when removed.
The overrunning clutch attachment flange at the aft end of the housing was fractured, and the outer race at the aft end was also fractured. The outer race fracture consisted of a circumferential portion, a spiral portion extending more than 360°, and a longitudinal portion linking the spiral faces, with features consistent with fatigue cracking. Cracks were perpendicular to the axis of rotation. The subassembly fracture surfaces showed evidence of torsional overload.
The lower arm of the left upper engine mount was fractured under tensile overload, and the upper arm of the right upper engine mount was bent to the right and cracked with a compression overload failure. Neither crack exhibited corrosion. Cracks were also observed on the forward surface of the center (lower) engine mount, partially obscured by paint. After paint removal, orange oxidation was noted on most of the crack surface, extending about 25% of the circumference and oriented vertically. The center engine mount fracture was consistent with overload, including in weld heat-affected zones; no evidence of crack propagation was found.
The engine-to-transmission driveshaft was examined at the manufacturer's facility and displayed no anomalies.
Medical and Toxicological Information
The Georgia Bureau of Investigation performed an autopsy on the pilot, which determined the cause of death as multiple blunt force injuries. Toxicology testing conducted by the Federal Aviation Administration Forensic Sciences Laboratory detected diphenhydramine (54 mg/dL in blood, also in liver), atropine (blood and liver), atorvastatin (liver only), pioglitazone (liver only), and midazolam (liver and blood). No ethanol was detected in blood. The detected medications were consistent with treatment for cholesterol and allergies and with postaccident emergency care.