Traffic flows are highly dynamic. Traffic densities vary locally throughout the day, indicating potential for idle descents outside of night hours. Alternatively, fixed-FPA descents can be flown with lower uncertainty. This thesis presents the development of novel per-flight criteria for executing idle and fixed-FPA descents from cruise to the Initial Approach Fix (IAF), using associated trajectory uncertainties. The influence of the criteria on the number of successful idle descents is assessed throughout a 24-hour operation. Trajectory uncertainty models were identified from simulations under various wind conditions. Using conflict probabilities, nominal aircraft spacing, and IAF arrival times, descent criteria sets were developed. The number of successful idle descents was evaluated for various reference scenarios with execution restrictions in time frames, developed criteria sets, and trajectory uncertainties. The results show conditional inverse relationships between the trajectory uncertainty, reference scenario and criteria strictness, and the number of successful idle descents. Scenarios with stricter time restrictions contain fewer successful idle descents. This also holds for stricter criteria, provided that aircraft spacing does not conceal the effect of the different criteria. Similarly, higher trajectory uncertainty reduces the number of successful idle descents, provided that, additionally, the criteria set was not too strict to conceal the effect. At least 50% of the aircraft descending outside of peak hours could complete an idle descent, regardless of scenario, criteria set, and uncertainty set. Including peak hours, this changes to 40% of all descending aircraft. The difference between high and low uncertainty remained below 2% of all flights for all explicitly developed criteria and scenarios. The theoretical maximum is found when all aircraft fly idle descents in the allocated time frames. This is 76% outside peak hours and 68% overall. This research provides a foundation for assigning idle descents and demonstrates their potential by allowing them outside night hours.

Reducing the emissions of ultra-fine particles in the vicinity of airports to minimise detrimental health effects for near-airport residents and airport personnel has been the main objective of the project. This report details the realisation of this goal which was done by designing a hybrid aircraft with notable improvements in the efficiency and emission characteristics. The aircraft in question is named the ’Low Emission Alternative Fuel’ aircraft, or ’LEAF’. Design of essential components and systems is presented along with evaluation of aspects needed for LEAF aircraft to enter the market by 2035.