CORROSION OF AIRCRAFT structure has plagued the airline industry since the use of metals in aircraft manufacture. It is costly both in unscheduled downtime and man-hours required for repair. The International Air Transport Association (IATA) reported in 1983 that corrosion cost the airlines between $8 and $20 per flight hour [1]. These numbers do not reflect the unscheduled downtime, both at the main bases and route stations, nor the additional corrosion inspections of aging airplanes recently mandated by the regulatory agencies. In fact, unlike fatigue damage, corrosion is extremely difficult to predict, i.e., when and where it will start, how fast it will progress, or how much damage it will cause. Because of this unpredictability, corrosion inspections are an integral part of an airline's maintenance program, and make up a significant part of its cost.