Enabling Condition Based Maintenance

MIL-STD-1530D describes the Aircraft Structural Integrity Program (ASIP), which defines the requirements to achieve structural integrity for USAF aircraft. Since its inception, inspection cost and asset availability has been driven by the constraints of non-destructive inspection (NDI) techniques that often require tear-down at depot locations and inspection by specialized trained experts. While this approach has proven extremely safe, alternative means of compliance (AMOC) are sought to reduce costs and down-time without increasing risk. To that end, the recent D-revision has included Structural Health Monitoring (SHM); an NDI technique that uses in-situ sensing devices to detect damage. SHM introduces many potential benefits through inspection automation without the need for depot tear-down. This revision dictates that the SHM probability of detection (POD) must be considered when determining its detection capability and monitoring intervals, using processes aligned with the statistical methods described in MIL-HDBK-1823A. The proposed effort seeks to establish a statistically equivalent probability of detection (SEPOD) approach to evaluate SHM inspection capability to facilitate its introduction within ASIP, thereby enabling condition based maintenance (CBM). This approach will be validated for a Carbon Nanotube (CNT) based crack-gauge through a comprehensive test matrix, including airworthiness assessment, leading to instrumented flight testing for an F-15.