Evaluation of Effectiveness of Non Destructive Testing Techniques for Inspection of Critical Aircraft Components- A Case of the Kenyan Aviation Industry

Abstract

Aircraft structural defects account for 33.3% of the aviation accidents in Kenya. This study evaluated the effectiveness of four types of NDT methods; ultrasonic inspection, radiography, visual testing and magnetic particle inspection being used in aviation industry, specifically for their sensitivity, accuracy, and reliability. It involved the use of in-service aircraft engine and landing gear components to evaluate structural defects during scheduled and unscheduled maintenance. This study was motivated by the need to improve our understanding and application of different NDT methods in defect identification in critical aircraft components. One hundred and one (101) aircraft samples were inspected at the following NDT Laboratories; Institute of Nuclear Science and Technology, University of Nairobi, a commercial airline in JKIA and in the security department, between July 2017 – April 2019. The results show that 50% of all the components inspected for landing gears assemblies had crack defects (1.9 mm-14.8 mm), while the engine components, had the cracks defects (1.00 mm- 220 mm), with highest proportion in combustion chamber and the turbine sections at (24.4% each), followed by the exhaust section at 14.6%. Other engines components had less than 10% of other defects; corrosion, disbond and delamination. In this study, the following defects were found; cracks (60%), corrosion (6%), delamination (2%), disbond defects (2%). Twenty nine samples (30%) had no defects. In conclusion, the study identified the structural defects in the landing gears and engine components; fatigue cracks, corrosion, delamination and disbond defects, using four NDT methods. The most effective NDT method for use in routine inspection of aircraft is boroscopic, which was sensitive to small size defects (> 2.5 mm) with the highest Probability of Detection (POD) at the 95% confidence limits. Visual inspection by magnifying glass is generally sensitive to larger size defects (>56.2 mm). MPI method is appropriate in defect detection of both surface and subsurface defects of ferrous materials. The application of UT method was appropriate for use to subsurface defects. The study recommends; to increase the frequency of aircraft inspections and further research on corrosion related defects upon recommendation to and approval by Original Equipment Manufacturers (OEM). The results of this study will contribute to improved safety regime and maintenance regime in the aviation industry in Kenya for extended aircraft service life, considering that aircrafts operate in the tropical climatic conditions and are prone to high rates of wear and tear of components.