###### Abstract  
This paper presents an advanced methodology for the detection of damage in aircraft composite materials based on the sensor fusion of two image-based non-destructive evaluation techniques. Both of the techniques, phased-array ultrasonics and infra-red thermography, are benchmarked on an aircraft-grade painted composite material skin panel with stringers. The sensors systems for carrying out the inspections have been developed and miniaturized for being integrated on a vortex-robotic platform inspector, in the framework of a larger research initiative, the Horizon-2020 'CompInnova' project. a 2021 11  
aircraft inspection worthiness and the development of reliable, automated, and synergistic techniques for capturing barely visible damage on aircraft. Currently, manual point-to-point inspection using conventional ultrasonic transducer and line-by-line Phased Array (PA) wheel probe [4] are used as a fundamental quantitative method, as per schedule-based maintenance for in-service inspections of composite skin surfaces. Such inspections are tactical and categorized in A-, C-, and D- checks, depending on the level of detail with respect to the aircraft age, hours in service, and the number of landing/take-off cycles. D-checks are the most thorough, involving a series of extremely detailed inspections of the fuselage skin and wing skin surfaces, requiring a minimum defect detectability of 6 \(\times\) 6 mm, and carried out approximately every six years. For an aircraft, like an Airbus A320-200, a D-check can last up to six weeks and cost up to $1.8 million [5]. The automation of in-service NDT inspections can lead to reduced cost, by an increase in the availability of aircraft [6]. Consequently, there is both research and industrial interest in reducing the time and cost of aircraft maintenance, especially during C and D-checks maintenance, which involves detailed NDT inspection. The automation of slower point-to-point ultrasonic inspection has received considerable attention in the oil and gas sectors, for tank and pipe inspection; a substantial number of mature solutions based on magnetic adhesion mobile robots have been suggested. There are only a few automated solutions for in-service inspection of aircraft using conventional ultrasonic transducers, like the MAUS-V system based on Cartesian scanners and flexible tracks with suction pads as adhesion [7; 8; 9]. Moreover, the application of these scanners is limited by the length of the scanner arms and it needs to be moved and fixed sequentially to cover a large area, thus increasing the time that is required for inspection. When compared to the point-to-point inspection method, full-field inspection NDT methods, such as infrared thermography (IRT) and shearography, have the inherent advantage of being non-contact and can scan large areas for defects in composites without the need for couplant agents. In recent years, full-field non-contact IRT has proved to be effective in detecting impact damages in aircraft CFRP composites, while new thermographic methodologies are constantly being improved at both the hardware level and post-processing stages to offer improved defect characterization [10; 11; 12; 13; 14; 15]. IRT is rapid, contactless, and accurate, and it allows for automation for minimal operator involvement, hence offering the potential for minimization of human error. It operates on the principle of the thermo-mechanical coupling under the thermoelastic effect, wherein a change in the stress field in the material is related to a change in temperature [16]. Hence, collection and analysis, by passive IRT, of thermal energy dissipated from material under stress, provides information of its internal mechanical state [17].