Hughes 369 N89ZC

Summary

On 5 March 2019 at about 16:10 local time, a Hughes 369 registered N89ZC, operated by Rotor Blade LLC, was involved in an accident near Talking Rock, Georgia, United States. One person was on board and one died. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

5 March 2019 at 16:10

Classification

Accident

Location

Talking Rock, Georgia, United States

Coordinates

34.5333, -84.5225

Aircraft

Hughes 369

Registration

N89ZC

Category

Helicopter

Year built

1981

Engines

1

Operator

Rotor Blade LLC

Operating rule

Part 133: Rotorcraft Ext. Load

Purpose of flight

External Load

Phase of flight

Not recorded

Route

Talking Rock → Talking Rock

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

ERA19FA118

1 person died.

A fatigue failure of the overrunning clutch subassembly due to abnormal bending loads due to cracks on the center engine mount, which resulted in an inflight loss of power. Contributing to the accident was the helicopter's low altitude and airspeed when the loss of power occurred, which precluded the pilot from successfully performing an autorotation.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

The helicopter pilot was using an aerial saw to trim trees along power lines. A witness reported that the pilot performed one pass, then returned for the second pass when the helicopter began to spin counterclockwise around its main rotor mast. During the second rotation, the helicopter impacted trees and terrain before coming to rest on its right side. Postaccident examination revealed a fracture of the overrunning clutch outer race and cracks on three of the engine mounts. While two of the three engine mounts cracks were likely a result of impact forces, the cracks on a third engine mount were likely present prior to the accident. The failure of the overrunning clutch subassembly outer race resulted in a loss of power to the main rotor system. Given the helicopter's low altitude and airspeed at the time of the loss of power, the pilot was likely unable to successfully initiate and perform an autorotative landing. Before its installation onto the helicopter, the overrunning clutch subassembly had been repaired, which included the installation of a new outer race. The accident helicopter operated with the overrunning clutch subassembly for about 33 flight hours until the accident occurred. Examination of the fracture surfaces revealed signatures consistent with fatigue and subsequent overload. The orientation of the crack in the circumferential plane was consistent with an anomalous bending load, such as an angular misalignment of the drivetrain, that drove fatigue crack initiation. Directionality of the deformation and fracture of the center engine mount was primarily in the vertical direction and the fracture surfaces exhibited evidence of oxidation, indicating that the cracks were present before the accident. Therefore, it is likely that the damaged center engine mount was the source of the anomalous bending loads that led to fatigue crack initiation and subsequent failure of the overrunning clutch outer race. The 100-hour/annual inspection of the engine mounts could be performed with the engine installed on the airframe, and the operator had done so; however, the presence of the engine could present difficulties for a mechanic in performing a visual inspection, particularly of the forward side of the center engine mount, where the cracks were located. Maintenance records indicated that, in the 9 months preceding the accident, the engine mounts were inspected six times with no anomalies observed. However, when the engine mount cracks may have developed and whether they would have been visible during any of the previous inspections could not be determined based on the available information..

Quoted verbatim from the NTSB record.