What happened
While performing a police mission at an altitude of less than 500 feet above ground level, the helicopter experienced a sudden loss of engine power. Due to the loss of power, the pilot was unable to maintain rotor RPM or reach a suitable landing area. The aircraft struck trees and a light pole, subsequently making a hard landing on a road before sliding into a fence.
The investigation
Mechanical examination of the engine, which had only 45.7 hours of total time, revealed that the #2 connecting rod had separated from the crankshaft. A torque check performed on the remaining connecting rod bolts showed that all were below the minimum specified requirements.
Investigation into the manufacturing process found that a work action (strike) was in effect at the engine manufacturer during the period this engine was assembled. During this time, production continued using management and replacement workers. It was determined that the crankshaft had been replaced during assembly for an unknown reason. Following the crankshaft replacement, new connecting rods were attached but were not properly tightened. The two assembly stations identified as most likely responsible for the crankshaft replacement and the failure to tighten the bolts were manned by replacement workers. While long-term employees were familiar with the correct documentation procedures for a replaced crankshaft, there were no specific written instructions available for the replacement personnel.