Technical Justification for an Ultrasonic Inspection Procedure Applied to a Helicopter Component

For many non-destructive evaluation (NDE) applications, traditional probability of detection (POD) assessments are impractical because of the cost, time, and complexity associated with manufacturing and preparing the required specimens representative of in-service conditions. Various alternative methods have been developed to reduce the number of test specimens required for the reliability estimation.

Technical justification is a process that includes analytical and experimental evidences, physical reasoning, summary and recommendation. Those are gathered and compiled in a structured format to verify that the targeted inspection technique, equipment and written procedure conform to the requirements and can meet its stated objective. Inspection qualification through technical justification minimizes the reliance on the manufacturing of test pieces and their time consuming inspection trials. In this paper, this promising approach is applied to demonstrate the reliability of an ultrasonic NDE procedure for the inspection of a helicopter upper tail-cone assembly. It is aimed to provide comprehensive evidence for determining whether the minimum detectable discontinuity size by the existing ultrasonic inspection procedure can be reduced from 1.27 mm (0.050 in.) to 0.64 mm (0.025 in.), without compromising the current level of confidence.