# Disposal and Recycle Economic Assessment for Aircraft and Engine End of Life Solution Evaluation
## 6 Analysis and Result Discussion
### Averaged Data Set and Economic Indicators
#### 6.1.2 Sensitivity Analysis for Averaged Data Set
We can see that the individual sensitivities of the D&R cost and residual value are different for \(I_{D\&R}\) and \(I_{D\&R\_NPV}\). This difference is caused by the mathematical formulation of those two indices: \(I_{D\&R}\) places the disposal and recycle cost in the denominator position, while the D&R cost is a subtraction item in \(I_{D\&R\_NPV}\). When \(\Delta x_{i}=0.99x_{i}{{}^{-}}\), the D&R cost is close to zero, which significantly increases the \(\text{I}_{\text{D\&R}}\) and illustrates a very sensitive feature. Considering the **total sensitivity** for \(I_{D\&R}\), i.e., \(\phi_{D\&R}^{T}(i)^{+}\) and \(\phi_{D\&R}^{T}(i)^{-}\) in Figure 4a,c,e, the salvage value is the most sensitive, and the second sensitive factor is the D&R cost (\(\Delta x_{i}=0.1x_{i}{{}^{+}}\), \(\Delta x_{i}=0.5x_{i}{{}^{+}}\)), while D&R cost is the most sensitive and salvage value the second-most sensitive when \(\Delta x_{i}=0.99x_{i}{{}^{+}}\). Increasing the D&R cost and residual value will result in negative impacts, while increasing salvage value introduces a positive effect (all \(\Delta x_{i}{{}^{+}}\) cases). With negative model input changes, the salvage value is the most sensitive (all \(\Delta x_{i}{{}^{+}}\) cases), the second-most sensitive factor is the D&R cost when \(\Delta x_{i}=0.1x_{i}{{}^{-}}\), and the residual value when \(\Delta x_{i}=0.5x_{i}{{}^{-}}\) and \(\Delta x_{i}=0.99x_{i}{{}^{-}}\). Decreasing D&R cost and residual value introduces positive impacts, while decreasing salvage value introduces a negative effect (all \(\Delta x_{i}{{}^{-}}\) cases). According to Figure 4b,d,f) \(\phi_{D\&R\_NPV}^{T}(i)^{+}\) and \(\phi_{D\&R\_NPV}^{T}(i)^{-}\), the most sensitive factor for \(\text{I}_{\text{D\&R\_NPV}}\) is the residual value in terms of the total sensitivity, and the D&R cost is shown as the second-most influential factor (all \(\Delta x_{i}{{}^{+}}\) cases). Increasing the D&R cost, residual value, and salvage value all introduce negative influences on the change of \(I_{D\&R\_NPV}\) when \(\Delta x_{i}=0.1x_{i}{{}^{+}}\) and \(\Delta x_{i}=0.5x_{i}{{}^{+}}\). However, increasing the D&R cost and residual value have negative impacts, and increasing the salvage value has a positive impact when \(\Delta x_{i}=0.99x_{i}{{}^{+}}\). The negative model input change for \(I_{D\&R\_NPV}\) shows that the salvage value is the most sensitive, while the residual value is the second-most sensitive parameter (all \(\Delta x_{i}{{}^{-}}\) cases). Decreasing the D&R cost and residual value produces positive impacts, while reducing the salvage value introduces a negative effect (all \(\Delta x_{i}{{}^{-}}\) cases). In view of the **interaction sensitivity** for \(I_{D\&R}\) (Figure 4a,c,e) \(\phi_{D\&R}^{I}(i)^{+}\) and \(\phi_{D\&R}^{I}(i)^{-}\), the most sensitive model input is the salvage value, and the D&R cost is the second-most influential parameter (all \(\Delta x_{i}{{}^{+}}\) cases). Increasing the D&R cost and salvage value introduces negative impacts (all \(\Delta x_{i}{{}^{+}}\) cases), while increasing the residual value introduces positive influences on input interaction induced output change. In terms of negative input changes, the interaction sensitivity of salvage value is the most sensitive, while the D&R cost is next (all \(\Delta x_{i}{{}^{-}}\) cases). Reducing the D&R cost and salvage value has negative influences, while decreasing the residual value induces a positive interaction change on \(I_{D\&R}\) (all \(\Delta x_{i}{{}^{-}}\) cases). However, it is noteworthy that the interaction sensitivity is negligible for all positive input changes when compared with their counterpart of negative changes for \(I_{D\&R}\). From Figure 4a,c,e) \(\phi_{D\&R\_NPV}^{I}(i)^{+}\) and \(\phi_{D\&R\_NPV}^{I}(i)^{-}\), the interaction sensitivity of the residual value, salvage value, and D&R cost for \(I_{D\&R\_NPV}\) illustrate equal interaction sensitivities for all \(\Delta x_{i}{{}^{-}}\) cases. The increase of the three model inputs has a negative influence on \(I_{D\&R\_NPV}\).