# Analytical Model for Enhancing the Adoptability of Continuous Descent Approach at Airports
## 7 Conclusions  
Based on the analysis of the parameters that govern CDA implementation during high traffic levels, such as the terminal maneuvering area (TMA) and the size of stacking space to arrange aircraft arrivals, an analytical model has been developed that aims at addressing the accommodation of more CDA operations than is presently done. Our analysis shows that the parameters that have significant impacts on CDA usage include airport arrival rate, capacity of the stacking space, and the minimum separation distance between aircraft arrivals. Although CDA usage is also affected by other parameters, such as wind speed, types of arriving aircrafts, and traffic levels at contiguous airports, we were able to capture the underlying relationship between these parameters and CDA usage, potentially helping air traffic controllers to decide on whether to adopt more CDA more often and using more quantitative information. In particular, we calculated the probability that an aircraft arriving within a brief period of time (say 15 or 30 min) would be denied CDA as a function of airport conditions. This may enable controllers to identify those periods of time when CDA should be anticipated, in other words, when the controller should plan on permitting CDA. This may lead to an increased use of CDA and, thus, result in lower noise, fuel consumption, and pollution. Furthermore, we established bounds for the maximum number of CDA descending aircrafts would fit within the stacking space, providing insight to the controllers on whether to permit a particular aircraft to use CDA or not. Finally, we illustrated our model using actual data from flights operated at Nashville International Airport (BNA).  
Future research opportunities include better support for air traffic controllers in analytically determining which arriving aircraft may be able to use CDA for a portion of their descent and when they should switch from SDA to CDA and vice versa. Another research possibility would be to analytically identify opportunities to put arriving aircrafts into a holding pattern for a short while if so doing would be result in it being able to use CDA after holding. Calculations could be performed to identify whether the additional fuel burned from holding (or adjustments to en route speed) would be more than compensated by the saved fuel from using CDA. In addition to the work presented in this paper, these research opportunities and others should be explored to improve aviation green operations and ensure air transportation sustainability.  
Conceptualization, L.L.A.-M., E.A.A. and R.J.M.; methodology, L.L.A.-M., E.A.A. and R.J.M.; software, E.A.A. and A.M.W.; validation, L.L.A.-M., R.J.M. and E.A.A.; formal analysis, E.A.A., R.J.M. and A.M.W.; investigation, E.A.A., R.J.M. and A.M.W.; resources, E.A.A.; data curation E.A.A. and A.M.W.; writing--original draft preparation, E.A.A. and R.J.M.; writing--review and editing, R.J.M.; visualization, E.A.A. and A.M.W.; supervision, L.L.A.-M.; project administration, E.A.A. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research received no external funding.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Conflicts of Interest:** The authors declare no conflict of interest.