Issue 78

C. Vendittozzi et alii, Fracture and Structural Integrity, 78 (2026) 519-540; DOI: 10.3221/IGF-ESIS.78.30

spectral signatures and changes in response persistence across separate field recordings. Across the two datasets, comparable sensor-dependent frequency families were observed within the analyzed band. In particular, the response was organized around low-end components in S1–S2, a mid-frequency family near 150 Hz in S3, and a high-frequency family near 427– 429 Hz in S4. These recurrent frequency regions should be interpreted as case-study evidence of structured spectral organization in the measured FBG response, not as statistically validated repeatability, modal identification, damage detection, or hard-landing classification. Ridge trajectories, band-limited descriptors, and per-event spectra provide compact and complementary representations of these frequency families, enabling response-based comparison across sensors, events, and datasets. The present study remains limited by the absence of synchronized avionics or other independent operational references, the lack of explicit temperature compensation, and the restricted number of analyzed recordings. Consequently, the detected events should not be interpreted as independently validated touchdown instants or operational-state labels, and the extracted descriptors should not yet be used for structural-integrity or HUMS decision-making. Future work should include synchronized operational references, dedicated temperature compensation, a larger set of labeled flights and repeated maneuvers, and comparison with conventional sensors, modal data, or numerical models before the descriptors can be used for decision-oriented maintenance or usage-monitoring applications.

A CKNOWLEDGMENTS

T

he authors thank the CNVVF flight crews and maintenance teams for their support, and the project partners for their guidance on installation and safety reviews.

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