## 2 Literature Review  
Landing gear or the undercarriage of an aircraft is one of the critical systems in an aircraft, especially during taxiing, take-off and landing. It performs vital functions, such as supporting the weight of the aircraft, absorbing impact upon touchdown, and providing braking and directional control. Typical parts of a landing gear include oleo strut, tyres, steering actuator, up and down locks, trailing arm or telescopic legs, and retracting actuator [11]. The braking system provides the braking action, which reduces braking distance and consequently increases payload capacity [12]. Commercial aircraft have primarily relied on hydraulic and pneumatic systems for most of their actuation systems. Recent commercial aircraft platforms have seen the introduction of electromechanical actuation systems in an attempt to utilise electrical power in more systems due to potential favourable advantages, such as a reduction in weight, fuel costs, and operating costs. Moreover, electrical power can be stepped up and down, stored, and, in turn, controlled and distributed to other systems easily according to their requirements due to advancements in the field of power electronics [4]. With the introduction of a 100 per cent electrical actuator in the A380's thrust reversal system and B787 replacing its pneumatic circuit with an electrical counterpart in the braking system propelled, the move towards More Electric Aircraft, thereby making the possibility of achieving All-Electric Aircraft, appears plausible in the near future [2]. Other major players in the industry have also adopted the MEA approach, with SAFRAN developing a fully electrical braking system and BAE introducing electrical flight controls to military aircraft [12; 13]. The incorporation of more electric components and actuators demands greater electric power generation, thereby requiring cooling and control systems of greater complexity. It is also worth noting that a significant weight reduction benefit of switching from hydraulic/pneumatic to electric actuation will only be realised once significant improvements have been made to the current power electronic modules. Another major challenge with MEA is evaluating the safety and reliability of the new designs. The cost and effort required to secure the initial certification for these new designs are considered prohibitively high, as the aerospace industry relies very much on legacy certification. Hence, the use of digital technology for system design and testing acquires a bigger dimension for new technology introduction [14; 15; 16]. Integrated Vehicle Health Management (IVHM) was first proposed by NASA in 1992 to determine the health of systems before, during and after their period of operation, with the goal being to avoid catastrophic failures. By introducing IVHM, NASA hoped to reduce maintenance and labour costs, and increase reliability and availability of equipment [17]. IVHM helps evaluate the health of systems in the aerospace sector through four approaches: Diagnosis, Prognosis, Automated Inspections, and Anomaly Detection. IVHM aims to provide a holistic approach to vehicle health management. Until its introduction, the health of individual components was monitored. The goal of IVHM is to assess the overall health of the vehicle by integrating the health status of various components and taking the inter-dependability of systems into account. IVHM intends to achieve this by incorporating various hardware and software into the system, such as sensors, reasoning algorithms, maintenance planners, databases for storing health parameters, etc., which aid in monitoring the health during operations. Fault diagnosis aims to identify the fault that has occurred from the control characteristics and sensor data available. It involves monitoring system characteristics for anomalies and analysing them to determine the type and nature of fault that has occurred. Fault prognosis focuses on predicting the future health condition of the system.