This research investigates detection of fastener failure in a thermal protection system. Since fastener failure is a global damage state, the low-frequency dynamics of the thermal protection system in the healthy state are experimentally taken in the laboratory to validate a finite element model representing the physics of the structure. Then, fastener failure damage states are simulated using the validated model. The damaged mode shape results are compared to the healthy mode shape results to quantify the damage. Two damage metrics—the normalized coordinate modal assurance criterion (NOCOMAC) and the normalized coordinate modal assurance criterion summation (NOCOMACSUM)—were created from the mode shapes to improve on the localization obtained from existing mode-based metrics: the modal assurance criterion (MAC) and coordinate modal assurance criterion (COMAC). The NOCOMAC and NOCOMACSUM demonstrate improved damage localization versus the MAC and COMAC.