Towards improving a scanning instrument capable of detecting/evaluating ply cord fatigue damage, which is a likely cause of the zipper mode of failure in steel-reinforced radial truck tires, an air-coupled transducer was used to replace a contact ultrasonic rolling transducer without reducing the probability of defect detection. By reducing the number of moving parts in the sensing unit, the instrument increased its robustness to better endure the environment of a new tire or retreading facility for on-line inspection of new or used tires. The instrument continues to be production oriented and capable of producing color-coded scans, thereby reducing the possibility of damaged tires causing property damage or personnel injury when being serviced. The results of two tires, one with seeded defects and other with field fatigue damage are presented and discussed.