Improved Eddy current techniques for the Aerospace Industry

It is estimated that over 25% of the world's commercial airline fleets are composed of aircraft over the age of 20 years. As a result of these aircraft exceeding their initial projected lifetime the issue of in-service inspection has become critical for the safe and economical management of fleets. The requirement for reducing inspection time by minimising 'false calls' and avoiding inspection preparation, has to be balanced against the needs for a high confidence level in the accuracy of the inspection. Research programs currently being conducted include the ARINC research on behalf of the USAF and the Sandia National Labs research for the FAA, which are addressing the issue of procedure definitions for the inspection of ageing aircraft and evaluating a range of different methodologies including Eddy Current, Ultrasonic, Magnetic Particle, Radiographic and Visual. Eddy Current is presently used in aerospace for over 50% of all applications for the detection of the most common material conditions that might lead to serious flaws. This covers applications for fastener hole inspection, surface and sub-surface cracking, conductivity measurement, and corrosion (which accounts for a high proportion of maintenance actions on ageing aircraft). New techniques such as FastScan allow the detection of smaller hidden cracks associated with fasteners, than was previously possible and cracks which have not yet emerged from beneath the fastener head are readily detectable. Similarly equipment is now un routine use that allows automated inspection of aircraft wheels. For speed and confidence in the accuracy of the inspection, it is essential that the operator can take the instrumentation into places of limited access and conduct the inspection, whilst being confident that the unit will give indications that are unambiguous and easy to interpret. It is this combination of instrument capabilities and operator knowledge which makes the most cost effective and reliable form of inspection. The industry emphasis is now on lightweight, high performance instruments which can address a wide spectrum of eddy-current inspection techniques from high to low frequency, dynamic rotating, skin inspection with fasteners in-situ and conductivity measurements with the benefit of dual frequencies.