Arrow Falcon Exporters, Inc. OH-58C N912HP accident near Fresno, California

Probable cause

The loss of engine power due to fatigue failure of a second stage compressor blade.

NTSB analysis

The pilot reported that he had filled the spray tanks with water and had lifted off from a platform on the back of a truck when he heard three loud noises followed by a loss of engine power. The pilot initiated a hovering autorotation to the landing platform; however, was only able to maneuver the forward portion of the helicopter over the platform. Subsequently, the helicopter slid off the platform and impacted the ground tail boom first, resulting in structural damage to the tail boom and fuselage. Examination of the engine revealed that 15 third stage compressor vanes were fractured near the root and had separated. The majority of the separated vanes were located in the lower compressor case half. The remaining attached vanes were bent over in the direction of engine rotation. A single second stage compressor vane located in the lower case halve was fractured near the root and had liberated. Multiple third and fourth stage compressor blades had leading edge damage. One second stage vane airfoil was separated and the area of separation was found consistent with high cycle fatigue (HCF). An additional second stage vane airfoil exhibited a crack, consistent with HCF near the root, but it did not separate. A Semi-quantitative x-ray energy dispersive analysis (XEDA) revealed deposits at the suction side vane root were consistent with oxidized braze alloy, indicating the braze alloy was exposed during engine operation. It was also found that the chemistry, microstructure and hardness of the second stage vanes were consistent with component specifications.

Text from the NTSB. Open the NTSB docket for LAX08LA195 for the full record.