The biggest aircraft manufacturers Boeing and Airbus have significantly increased the use of composites in the production of their next-generation commercial aircraft. Driven by the need to reduce aircraft weight and thus optimize operational costs manufacturers and material suppliers increasingly invest into developing innovative solutions designed to integrate structures into more complex single components that are manufactured in “one shot”. With the dramatic increase in the usage of composite materials the non-destructive testing (NDT) requirements are becoming more and more complex in both manufacturing and in-service maintenance. The question is whether the increasingly complex NDT procedures threaten to become the bottleneck of the entire manufacturing and maintenance process.
The NDT and inspection of composite structures, both for manufacturing quality assurance and for in-service damage detection, have prompted the development and adaptation of a number of methods and techniques over the years. Presently approx. 70-80% of aircraft NDT is performed on the airframe, structure, landing gears and remaining 20% or so is carried out on engine & related components. The most commonly applied NDT methods aimed at eliminating aircraft defects and ensure a high degree of quality & reliability include: liquid penetrant testing, magnetic particle testing, eddy current tests, ultrasonic inspection, radiography (x-ray/gama ray), visual/optical inspections, sonic/resonance testing, infrared thermography, shearography, X-Ray tomography, laser ultrasonic, acoustic emission, neutron radiography, leak testing, holography and microwaves.
‘There is no question that the success of the airplane industry is highly dependent on NDT. Without NDT the cost of maintaining and operating airplanes would increase dramatically, while the safety of flying would decrease significantly. The NDT specialists are continuously challenged to develop new techniques for non-destructive testing and to offer new methods for data handling. On the other hand, the best equipment in the world doesn’t guarantee the best quality services and safety. Most of the aviation industry requires technicians to be trained, qualified and certified in accordance with the EN4179 standard, Aerospace Standard for Certification and Qualification of Non-destructive Test Personnel. Currently, training, qualification and proficiency of NDT personnel in the aviation industry are critical,’ noticed Ignas Avizonis, Instructor at FL Technics Training.
According to I.Avizonis, NDT tasks require trained professionals who can master a variety of different NDT techniques to determine a complete and accurate status of aircraft. In-service NDT inspection requires skills and knowledge that are not possessed by many professionals in the aviation maintenance or other industries. NDT technicians should be presented with explicit instructions designed specifically for the inspection of aircraft in the field. They should possess thorough knowledge of aircraft design, metal and composite materials, manufacturing, repair, and flaws associated with different types of aircraft. They must also be well aware of all the potential in-service issues such as corrosion, fatigue and various types of structural damage. Moreover, every NDT specialist must have the adequate amount of hands-on practical experience gained whilst working on actual retired aircraft, not to mention the full awareness of the construction materials and material forms, thickness, thickness variations, and the location and nature of bonded substructures. For example, a minimum of 1600 Hrs of practical experience for Level 2 in Eddy Current and Ultrasonic methods are a must for the personnel seeking certification in accordance with EN4179 at a Part 145 certified organization.
New Part 66 regulations make 2012 the ‘transition year’ in the field of Part 145 and Part 147 training. According to the new rules, at least 2 weeks-long practical training must be conducted at a Part 147 certified training institution for everyone seeking their Aircraft Maintenance Licence (AML) endorsement with aircraft type. Those seeking it for the very first time must also carry out ‘on the job training’ at a Part 145 certified organization.
‘It is therefore very important that all technicians receive refresher training, especially with regard to the areas and methods which they may not be using on a regular basis but which may be in need of urgent application on short notice and with no preparation,’ states I.Avizonis.
Hands-on exercises provide the students with the opportunity to see not only how different NDT methods respond to different flaws and flaw locations, but also how fabrication issues can really affect the results. The students are allowed to design and fabricate their own specimens so they can develop a better understanding of the relationship among the material, fabrications, defects and NDT capabilities. Training and examination must be performed by someone who has the knowledge, experience, and resources to provide the necessary aerospace point of view.