With the evolution of light and stiff composite technology as a viable alternative to metals, wide-spread applications of bonded composite structures are being accepted in the aerospace industry. Although several bonded composite structures are currently in-service, the certification cost often negates the demonstrated benefits of composite material based structures. One of the key requirements for the certification and the subsequent implementation of the new composite-composite bonded structure is the assurance of the integrity of the adhesive bond joints. In this paper, a reflection frequency spectrum of the reflected ultrasonic oblique wave (in a pitch-catch mode) from an adhesively bonded graphite-epoxy aircraft wing-spar structure is obtained and mapped. Different types of programmed defects such as inclusions, voids, and interface contamination at the adhesive substrate were evaluated using the reflection factor technique.