What is a ndt mean in aviation?

Non-destructive testing (NDT) is a branch of material science for inspecting, testing, or evaluating materials, components or assemblies for characteristics associated with intended service without permanently altering their properties or form. Some NDT inspections utilize destructive testing (DT) as part of testing process. The term is generally applied to the inspection of materials and engineering constructions which is employed in conjunction with the design, fabrication, erection, maintenance and disposal of structural components by determining the physical and functional property requirements.