ERA24LA148

The pilot was conducting low-altitude, external-load tree-trimming operations when he heard a loud “boom,” and the helicopter entered a rapid descent. He maneuvered toward smaller trees to minimize the impact and briefly lowered the collective to preserve rotor rpm before raising it just before ground contact. The helicopter contacted trees and branches during the descent, becoming inverted after impacting the ground. The tail boom separated from the fuselage, and the main rotor blades were severely damaged and scattered throughout the area, as were various rotor head components. Postaccident examination of the drivetrain, clutch, and associated components revealed no evidence of pre-impact mechanical failure or malfunction. Examination of the engine revealed severe damage to the compressor inlet and rotor assembly, with multiple fractured blades from stages 1 through 5, consistent with pre-impact hard-body ingestion. Metallurgical analysis found no evidence of fatigue or manufacturing defects, and all other engine systems and components were free of pre-impact anomalies. Although the source of the ingested material could not be determined, the low-altitude operating environment near trees made it likely that debris from the trimming operation was ingested into the engine, resulting in a sudden loss of power.

On March 18, 2024, about 1720 eastern daylight time, a Hughes 369D helicopter, N102SU, was substantially damaged when it was involved in an accident near Belleville, West Virginia. The commercial pilot was seriously injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 133 rotorcraft external load flight. According to the pilot, he had completed several tree trimming flights throughout the day with no anomalies. During the accident flight, while trimming trees above a creek, he encountered encroaching tree limbs and was assessing whether the tree line could be trimmed safely. He then heard a loud “boom,” after which the helicopter entered a rapid descent. The pilot maneuvered toward smaller trees to minimize the impact; he briefly lowered the collective to preserve rotor rpm and raised it just before ground contact. He reported that he intentionally retained the external cutting saw, believing it might help absorb some of the impact forces. The helicopter was found inverted in mountainous, hilly terrain, with the aerial saw assembly still attached and the support pipe fractured at its midpoint. The tail boom was separated from the fuselage, and the main rotor blades were severely damaged and scattered throughout the area, as were various rotor head components. The helicopter’s nose section exhibited crushing damage consistent with contact with trees or branches during the descent. Postaccident examination of the helicopter’s drivetrain revealed no evidence of pre-impact mechanical failure. The Kaflex driveshaft and associated drivetrain components exhibited no cracks, fractures, or abnormal wear. The driveshaft was intact, with torque striping present on all fasteners except one, which showed partial stripe loss. The main transmission input coupling and clutch subassembly exhibited no anomalous damage. All splined connections were well-lubricated and free of wear or missing teeth. The clutch functioned properly, and both bearings adjacent to the sprag assembly rotated freely. The grease and oil were dark in appearance, consistent with normal use, and no metallic particles or abnormal odors were noted. Fluid levels were within specified limits. A follow-up examination of the engine revealed no evidence of pre-impact fire, damage, or malfunction. The engine remained securely mounted, and the engine compartment was intact. Continuity was confirmed through both the N1 and N2 rotor systems, although neither could be rotated by hand due to significant carbon deposits and coking on the turbine seals. The compressor inlet and rotor assembly sustained severe damage, with blades from stages 1 through 5 fractured near the hubs, consistent with hard-body ingestion. Metallurgical analysis revealed no signs of fatigue failure. A pressure control system check revealed no leaks.