Air tra?c has been growing rapidly for the past few decades and will continue to do so. Airports need to be able to coop with this increase, and thus increase their own capacity. However, due to the landing and departure operations, which take place at low altitudes, high noise levels are generated and a?ect the neighboring communities. This in turn limits the growth of airports that are located near inhabited areas, due to the restrictions on noise levels set by governments for airports. In order to reduce the aircraft noise, a number of solutions have been developed. Some of these solutions are on the aircraft level while the others are on the airport level. A number of solution implemented on the aircraft level are for example, noise e?cient engines and noise reducing fairings. The airport level knows the development of noise abatement operational procedures, such as the CDA. However, there are downsides to such a procedure, like the limitations that it only allows vertical optimization or ?ight at night. Therefore, a new noise abatement procedure has been developed called HeNAP, which stands for Helical Noise Abatement Procedure. As the name suggests it is a procedure where the descent approach is performed by means of a spiral. This allows the aircraft to perform a ?yover the inhabited areas at a higher altitude and perform a descent near the airport by means of a spiral. This would reduce the noise levels perceived by the inhabitants. Earlier research showed a decrease in noise levels but an increase in fuel consumption and time; however, it was never optimized with respect to these factors and at closely inhabited airports. Therefore: The aim of this project is to develop noise-optimal HeNAP approach trajectories using methods from optimal control theory. The noise bene?ts of the optimal HeNAP trajectories need to be assessed through comparison with conventional noise abatement procedures. In addition, an analysis needs to be made of the operational consequences of introducing HeNAP procedures. For this purpose, a GPOPS-based environmental optimization framework for HeNAPs was created. By performing the research on the HeNAP and validating it at the same time, a set of research goals are investigated during this thesis: Develop a code for optimizing the HeNAP trajectories within GPOPS . Assess the in?uence of changing multiple variables such as the altitude, the helical radius and number of spirals performed before landing on the environmental optimization of HeNAP’s with respect to noise impact, fuel usage and time. The framework that is created in GPOPS for the HeNAPs combines a number of models in order to generate noise, namely, a noise model and an aircraft model. This combination results in noise generation of the trajectory ?own, and is processed further in a model that calculates the impact of the noise on inhabited areas. By means of sleep disturbance doseresponse relationship, the impact is converted into the number of awakenings. All of the models interconnect such that a gradient-based optimization is performed to optimize the HeNAP procedure. With the usage of Optimal Control Theory, the cost function, consisting of a weighted noise factor and fuel contribution, is minimized by means of a dynamic process in order to ?nd the optimal controls of the problem. With the help of the Radau pseudospectral method, the dynamics of the problem is accurately approximated. This allows the continuous problem to be discretized to change the in?nite-dimensional problem into a ?nite-dimensional nonlinear programming problem. This can be solved with a numerical solver and results in optimal controls and states that form the HeNAP trajectory. To assess the di?erent changes in altitude, radius and number of spirals and impact of the resulting solutions on the environment, for the majority of the time a single-phase optimization is used. However, in order to assess sections of the HeNAP trajectory, multi-phase optimization is sometimes used as well. The help of these optimizations simulates di?erent HeNAP routes until the most favorable one is found. A case study is performed in a highly inhabited area around Amsterdam Airport Schiphol. During this case study, a number of routes are simulated and investigated. Di?erent altitudes, radii and number of spirals are compared while adhering to the di?erent airspace regulations. Over 300 simulations have been performed, as this was an intensive trial and error process, eventually resulting in a number of cases over four di?erent optimization problems. These problems are de?ned as followed, minimum time optimization problem, minimum fuel optimization problem, minimum time and noise abatement optimization problem and ?nally minimum fuel and noise abatement optimization problem. The cases that are solved for these problems are as followed: Case 1: is a CDA procedure that is performed at an altitude of 7000 ft and minimum ILS approach distance of 6.2 NM. Case 2: is the ?rst HeNAP simulation and is run with an altitude of 7,000 ft and one spiral. Case 3 the altitude is changed from 7000 ft to 10,000 ft. Case 4 the altitude of case 3 is still in e?ect and the number spirals is changed from 1 to 2. The results of these cases are all comparable throughout the di?erent optimization problems. All of them reveal that the CDA procedure is the most favorable procedure as it has the least number of awakenings, fuel consumed and time needed to land. However, when relocating the population around the airport to the ?rst part of the trajectory it yields better results. Case 3 is then the most favorable case, with promising results. The changes in altitude for the HeNAP showed that by having a higher initial altitude the number of inhabitant awakened is reduced, however when the number of spirals is increased this e?ect is dismissed. The following recommendations might help improve/show more of the HeNAP possibilities. The ?rst recommendation that can be given, is to use the results that are found within this thesis and use them as a basis for the same research but within another area that might be less inhabited than the area around AAS and where the night-curfew is also in e?ect. Another recommendation that can be made is to add the wind and weather conditions to the GPOPS tool in order to get results that are more realistic and increase the reliability of the results and feasibility of the trajectories performed. A ?nal recommendation is to introduce better methods to avoid local minima within the GPOPS tool, this result in unnecessary delays. Nevertheless, the HeNAP procedure has great future possibilities only not within the Netherlands.