Incident Overview
A helicopter experienced a total loss of engine power, leading to a forced landing in a swamp. The aircraft, which was conducting mosquito control spray operations, sustained substantial damage during the landing.
Engine Inspection
Post-accident inspection of the engine identified damage to the compressor coupling shaft. Specifically, the splines on the turbine-driven end of the coupling shaft, which connects the compressor to the spur adapter gear shaft, were damaged.
Exhaust Collector Findings
Examination of the turbine end of the exhaust collector revealed a circumferential weld joining the mounting flange to the bifurcated duct. This weld was non-uniform, discontinuous, and exhibited a heat tint on both sides. Further inspection showed areas where the duct material adjacent to the weld was slightly buckled and displayed indications of impact.
Dimensional Analysis
The exhaust collector was dimensionally checked using a coordinate measuring machine (CMM). The CMM results indicated that the flatness of the attaching flange for the pilot diameter displayed localized variation. Per the manufacturer's specifications, the centerline of the collector is established from the turbine pilot diameter and its attaching flange surface. The discrepancies in these features resulted in a runout error on the gearbox pilot diameter.
Conclusion
The forced landing was necessitated by a total loss of engine power, with the subsequent investigation revealing damage to the coupling shaft and irregularities in the exhaust collector weld and dimensions. No further analysis or causal determination is provided in the source.