Purpose <p> In this study, a methodology for damage detection and localization in aeronautical structures based on Automatic Operational Modal Analysis and a strain-based damage index is presented.</p> Methods <p>The proposed approach enables the automatic extraction of strain mode shapes under operational conditions, relying solely on output measurements. Modal parameters are estimated using Stochastic Subspace Identification, with pole selection performed via Density-Based Spatial Clustering. The methodology is initially validated numerically on two different case studies: a stiffened cantilevered plate and a composite glider. In both cases, damage is simulated by locally reducing the stiffness of specific regions, and strain signals are collected from virtual sensors under spatially and temporally random excitation. The proposed approach is then applied to an experimental test on a manufactured composite glider model, instrumented with Fiber Bragg Grating sensors bonded to the wing surface.</p> Results and Conclusion <p>The numerical results demonstrate that the proposed methodology effectively detects and localizes damage across varying intensities, even under noisy conditions. Experimental results confirm the effectiveness of the methodology in real-world conditions, highlighting its potential for in-flight Structural Health Monitoring applications.</p>