NTSB Identification: CHI02LA163.
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Accident occurred Tuesday, June 11, 2002 in Jordan, MN
Probable Cause Approval Date: 02/05/2004
Aircraft: Bell 47G-2A-1, registration: N8542D
Injuries: 1 Minor.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The helicopter was substantially damaged during a forced landing to a swamp after a total loss of engine power. The purpose of the flight was to spray for mosquito control. Inspection of the engine revealed that the compressor coupling shaft to the spur adapter gear shaft had damaged splines on the turbine driven end of the coupling shaft. Examination of the turbine end of the exhaust collector revealed that the circumferential weld joining the mounting flange to the bifurcated duct was non-uniform, discontinuous, and displayed a heat tint on both sides. Closer examination revealed places where the duct material; adjacent to the weld was slightly buckled and displayed indications of being impacted. The exhaust collector was dimensionally checked on a co-ordinate measuring machine (CMM). The CMM indicated that the flatness of the attaching flange for the pilot diameter displayed localized variation. As the print specifies that the centerline of the collector is established from the turbine pilot diameter and its attaching flange surface, their discrepancies resulted in a run out error on the gearbox pilot diameter.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The loss of engine power due to improper maintenance by unknown maintenance personnel which led to a misalignment of the gearbox casing.

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