Incident Background
A helicopter that had previously experienced a tail rotor strike underwent an inspection of its tail rotor driveshaft. During the inspection, it was discovered that the adapter on tail rotor drive shaft number 4 had debonded and subsequently rotated on the shaft.
Metallurgical Findings
A metallurgical examination of the debonded adapter was conducted. The examination confirmed the presence of debonding, but the exact mode of failure could not be determined due to rotational damage sustained during the event.
Additional Adapter Issues
Further examination of other shaft adapters revealed that they also exhibited debonding. In these cases, the debonding was determined to have been caused by plastic blasting, a process that involves the use of plastic media for cleaning or surface preparation.
Inspection Procedure Discrepancy
The approved inspection procedure for the tail rotor driveshaft specifies the use of magnetic particle or fluorescent penetrant methods for detecting defects. The procedure does not call for the use of plastic medium blasting, which was identified as the cause of debonding in some of the adapters. The discrepancy between the approved inspection methods and the actual process used may have contributed to the condition of the adapters, though the investigation did not establish a direct causal link to the incident.
Conclusion
No further details were provided regarding the helicopter's operator, location, or the outcome of the flight. The investigation focused solely on the technical aspects of the driveshaft adapter debonding and the inspection practices involved.