# Disposal and Recycle Economic Assessment for Aircraft and Engine End of Life Solution Evaluation
## 4 Cost and Value Evaluation
### Disposal and Recycle Cost Estimation  
The cost estimation herein is based on the integration of the product, D&R process, and cost properties [42]. Complying with customer requirements for the EoL aircraft with considering the component function and materials, the EoL strategy and the detailed D&R process can be planned. The D&R process plan is generated based on the D&R process model and the engineering rules embedded in the model. For example, if it is an engine part to be reused in another aircraft, the engine should go through 'component management' and'reuse in other aircraft' steps, which contain detailed sub-steps, including remove, clean, repair, recovery, and recertification. These process steps are set up sequentially to represent the D&R process for this specific case. The total cost is then formulated by summing up the cost items for all process steps (see Equation (1)). The generalized D&R cost function includes the costs of all possible steps following the D&R process model. It includes storing, component management, disassembly & dismantling, material management, reuse in other aircraft, alternative reuse, land filling, energy recovery, secondary material down cycling (for low quality material(_lq_)), and secondary material recycling (for high quality material(_lq_)), plus resale. Dependent upon the D&R operational scenarios, either part of or all the process steps are performed. In other words, Equation (1) only includes the cost items incurred within the actual D&R practice. Other cost items of the process steps not incurred are denoted as zero. Next, each D&R process step cost can be obtained by aggregating the cost elements defined in a Cost Breakdown Structure (CBS). The CBS contains labor, material, and energy consumption incurred during each D&R process step, the facility, tooling & equipment costs used to facilitate the D&R process operations, the miscellaneous costs including the project management, and other overhead costs, as shown in Figure 3 (see Equation (2)). Equivalently, we can first sum up the process step costs for each cost element, then accumulate the cost elements to obtain the total D&R cost. This equivalence between those two aggregations can be expressed as in Equation (3). \[ \begin{array}{c}C_{D\&R}=\sum\limits_{k}C_{D\&R,k}=C_{D\&R,storing}+C_{D\&R, disassembly\&dismantling}+C_{D\&R,component\_management}\\ +C_{D\&R,material\_management}+C_{D\&R,reuse}+C_{D\&R,alternating\_reuse}+C_{D \&R,energy\_recovery}+C_{D\&R,land\_filling}\\ +C_{D\&R,reycling\_lq}+C_{D\&R,reycling\_lq}+C_{D\&R,reycling\_lq}+C_{D\&R, reuse}\end{array} , \tag{1}\]  
\[ \begin{array}{c}C_{D\&R,k}=\sum\limits_{j}C_{D\&R,k,j}=C_{D\&R,k,j, labour}+C_{D\&R,k,material}+C_{D\&R,k,energy}+C_{D\&R,k,facility}\\ +C_{D\&R,k,loading\&equipment}+C_{D\&R,k,miscellaneous}\end{array} , \tag{2}\]  
\[ \begin{array}{c}C_{D\&R}=\sum\limits_{k}\sum\limits_{j}C_{D\&R,k,j}=\sum \limits_{j}\sum\limits_{k}C_{D\&R,j,k},\end{array}  \tag{3}\]  
where \(C_{D\&R}\) is the total cost used for the overall D&R process. \(C_{D\&R,k,j}\) indicates a D&R cost item, \(k\) refers to a specific D&R process step (e.g., storing, disassembly & dismantling, etc. ), and \(j\) refers to a D&R cost element (e.g., labor, material, etc.). In practice, since the labor, material, and energy cost elements are directly associated with the process steps, they are easily extracted during the D&R operation. The other cost elements, such as facility cost, tooling, and equipment cost, are mostly one-time investments, and can either be estimated as a lump sum or be distributed over the D&R process steps to be aggregated later. It is also noteworthy that there are different D&R cost classifications, such as buy-back cost, transportation cost, tip and storage fee, labor cost, equipment investment cost, and recovery cost [43]. However, this kind of classification often confuses the process costs and the pure cost elements.