# Preliminary Impact Assessment of the Ad Hoc Separation Minima: A New Separation Mode
## 1 Introduction  
The most reliable traffic forecasts anticipate 16 million Instrumental Flight Rules (IFR) movements by 2050 in the region of the European Civil Aviation Conference (ECAC) [1], which represents a 44% growth in air traffic compared to the levels of 2019. Although this is a long-term forecast of demand growth, in the aviation industry, and specifically in the Air Traffic Management (ATM) system, action is needed now to meet future challenges. This strategic action requires a plan for research, development and implementation of new concepts and technologies. The SESAR program (Single European Sky ATM Research [2]) is an initiative aimed primarily at developing the future ATM system in Europe. This strategic program focuses on the definition, development, validation, and implementation of innovative technological and operational solutions to enhance various aspects of ATM [3]. These solutions are geared towards achieving benefits in four key performance areas (KPAs): capacity, safety, efficiency, and environment. Given this expected growth in air traffic demand, within the SESAR framework, it is crucial to address the capacity challenge without neglecting environmental concerns or compromising safety levels. In pursuit of these goals, SESAR proposes research into various solutions, which address different KPAs. Regarding the capacity KPA, several projects have been or are being performed to explore potential solutions. Among others, one of the investigated solutions is the dynamic configuration of airspace (DAC) [4], where the design/configuration of sectors adapts to traffic flows. Another solution developed [5] is based on Performance Based Navigation (PBN), specifically on the Required Navigation Performance (RNP) specifications of navigation. By meeting the required criteria (in terms of accuracy, continuity, etc. ), it is possible to increase capacity through the reduction in spacing between routes and the incorporation of new ones. Additionally, improvements in ATC support systems contribute to capacity enhancement. The solution developed in [6] aims to decrease the frequency of tactical Air Traffic Control (ATC) interventions by equipping Air Traffic Control Officers (ATCOs) with ground conflict detection and resolution (CD&R) tools reliant on an enhanced ground trajectory prediction based on improved aircraft data. In [7], the SESAR solution provides the en-route ATCOs with two services to assist them in the separation provision. Firstly, the Monitoring of Aircraft Trajectories (MONA) service offers trajectory monitoring with newly included alerts. Secondly, the CD&R functionality provides improved conflict detection and resolution capabilities. Regarding the environmental and cost-efficiency KPAs, some of the extensively studied solutions include the Continuous Descent Operations (CDO) [8; 9; 10] and Continuous Climb Operations (CCO) [11; 12; 13]. The impact of these coorfriendly trajectories (optimized descents and climbs) on emissions, fuel consumption, and noise is analyzed in [14; 15] (CDOs) and in [16; 17] (CCOs). Conversely, in general, the other concepts' main goal is not to achieve an environmental improvement. That is, in other concepts, the environmental benefits are generally achieved indirectly, as a consequence of improvements in other aspects. Examples of this include concepts such as Free Route or AMAN/DMAN. In the Free Route concept [18], aircraft are allowed to fly their chosen trajectories between entry and exit points in an airspace, without the need to follow published routes along conventional airways. As a result, the flown routes are generally shorter, leading to savings in flown distance, flight time, fuel, and emissions. The AMAN/DMAN solution [19] provides automated support for aircraft sequencing, assisting ATCOs in managing traffic arriving and departing from an airport. Because of sequence optimization, waiting times, the associated flown distances, fuel consumption, and emissions are reduced.