Ultrasonic technique to detect corrosion in DC-9 wing box from concept to field application

Current procedures to inspect for corrosion of T-caps in the wing box of the DC-9 require entry into the fuel tank for visual inspection. This paper describes the development of an ultrasonic technique to detect T-cap corrosion by scanning the multi-layered wing structure from the outside. The development of the technique is described from its conceptual phase, through the preliminary design of a prototype ultrasonic unit which was extensively tested in the laboratory and subsequently at the Northwest Airlines maintenance facility, to testing of the technique and the unit under field conditions at Northwest Airlines and the facility of Dee Howard, a major independent maintenance facility located in San Antonio, Texas, to plans for revision of the Service Bulletin. Field implementation of the new technique will provide major cost reductions by eliminating the need for fuel tank entry.