Aircraft are inevitably subjected to damage from various sources such as bird strikes, accidental impacts, and mechanical failures during operation, making reliable damage detection essential for ensuring safety and structural integrity. Early detection of potential structural issues through effective inspection systems is crucial to prevent accidents and extend the lifespan of aircraft. Non-destructive evaluation (NDE) methods are commonly employed during maintenance to assess aircraft structures. However, each NDE technique has specific strengths and limitations when evaluating damaged materials. This chapter introduces several NDE techniques, alongside advanced data registration and fusion models designed to overcome the limitations of individual NDE techniques. As an example, the chapter discusses the application of these models in assessing lightning damage to carbon fiber reinforced polymer structures. Emerging technologies such as artificial intelligence and automation are driving the development of NDE 4.0, which enables automated, accurate damage assessment in aviation. The chapter concludes by summarizing the strengths and challenges of current NDE data registration and fusion methods, and outlines future directions for NDE 4.0 to further enhance aircraft safety and maintenance.