## 2 Theoretical Background and Related Work  
To start, this section reviews the state-of-the-art research in the areas of collaborative decision making in air transport operations, as well as the use of digital twin-based training and intelligent automation in aviation. In complex environments and real-life situations, it is inevitable that most of the processes cannot be achieved by a \"one-man band\". Multiple stakeholders might be involved in the decision-making process according to their roles. In the context of air transport operations, pilots who operate the aircraft need to consider the potential effect of their operation on neighbouring traffic, the comfort of their passengers, the environmental impacts, the overall safety, etc. Therefore, the role of ATCOs is to regulate all of these factors from a macro perspective to provide a safe and efficient airspace. The complex nature of such a role demands high levels of human intelligence. As [PERSON], [PERSON], and [PERSON] [19] defined a team as two or more people possessing a set of shared goals with multiple information resources, the flight crews and the ATCOs could be considered as a team. Hence, there is a need for collaboration and teamwork among every contributing party to act together to achieve a set of shared goals. A shared mental model among collaborating parties should be achieved to ensure a promising team performance [23]. [PERSON], [PERSON], [PERSON], [PERSON], and [PERSON] [22] reviewed the situational awareness assessment approaches in aviation. The review suggested that shared situational awareness could be attained starting with the pilots. Flight crews first need to build and retain their situational awareness, as well as to notice any relevant events during their flying task. Then, they have to share their situational awareness and the relevant events with other members of the team and, most importantly, communicate with the ATCOs. While pilots usually are just concerned with their own aircraft, ATCOs can provide them with a more comprehensive understanding of the dynamics within the current airspace with the use of a time-dependant radar map. Several studies also attempted to examine the mental model disconnects between the pilots and the ATCOs. For instance, [PERSON] et al. [24] empirically investigated the mental model disconnects in a contextual perspective using a crew-based critical decision method (CDM) interview. The interview was conducted with pilots and ATCOs in Singapore with probing. Data were analysed qualitatively. It was discovered that flight crews might operate taking the passenger's comfort into account, while ATCOs expect flight crews to strictly comply with their instructions. In particular, during abnormal operations such as adverse weather and dense traffic, a shared situational awareness between the two might be harder to achieve. In addition to qualitative analysis, simulation techniques were also used to model and validate real-world collaborative decision-making processes. Agent-based model simulation was adopted by [PERSON] et al. [25] and [PERSON] et al. [26] to study the air transportation system's reliability and the mental model disconnects, respectively. In particular, the previous studies considered the aircraft as the agent as a function of the interactions between pilots and ATCOs. To eliminate potential human error, vocational training is one of the conventional strategies with extensive applications in the aviation industry. From pilots to ATCOs and aircraft maintenance professionals, on-the-job training is a crucial part towards building a solid foundation of required technical and nontechnical skills. Qualified pilots have to go through knowledge-based and practical-based training in a designated organisation approved by the relevant civil aviation authorities. The practical-based training for pilots usually starts with a digital twin-based platform before moving on to a real aircraft.