*Article* **Enabling Green Approaches by FMS-AMAN Coordination**

**Nils Ahrenhold \*, Izabela Stasicka , Rabeb Abdellaoui , Thorsten Mühlhausen and Marco-Michael Temme**

German Aerospace Center (DLR) Braunschweig, Institute of Flight Guidance, Lilienthalplatz 7, 38108 Braunschweig, Germany

**\*** Correspondence: nils.ahrenhold@dlr.de; Tel.: +49-531-295-1184

**Abstract:** Growing political pressure and widespread social concerns about climate change are triggering a paradigm shift in the aviation sector. Projects with the target of reducing aviation's CO2 emissions and their impact on climate change are being launched to improve currently used procedures. In this paper, a new coordination process between aircraft flight management systems (FMSs) and an arrival manager (AMAN) was investigated to enable fuel-efficient and more sustainable approaches. This coordination posed two major challenges. Firstly, current capacity-centred AMANs' planning processes are not optimised towards fuel-efficient trajectories. To investigate the benefit of negotiated trajectories with fixed target times for waypoints and thresholds, the terminal manoeuvring area was redesigned for an independent parallel runway system. Secondly, the FMS-AMAN negotiation process plan the trajectories based on time, whereas air traffic controllers guide traffic based on distance. Three tactical assisting tools were implemented in an air traffic controller's working position to enable a smooth transition from distance-based to time-based coordination and guidance. The whole concept was implemented and tested in real-time human-in-the-loop studies at DLR's Air Traffic Validation Center. Results showed that the new airspace design and concept was feasible, and a reduction in flown distance was measured.

**Keywords:** green approaches; FMS; AMAN; CDA; negotiation process

**1. Introduction**

Addressing environmental challenges, especially global warming, is more than ever a must for the community [1]. This matter is becoming an increasing priority at the regional and global level, which was already investigated by Crompton in 2009 [2]. Europe has made commitments to reduce aviation's environmental footprint [3], not only because of growing political pressure, but also due to the widespread social concern about climate change. This is triggering a paradigm shift in the aviation sector, since the sector is contributing to climate change, increasing noise, affecting local air quality and consequently affecting the health and quality of life of European citizens [4,5]. In 2020, air traffic movements drastically reduced due to the COVID-19 pandemic [6]. Currently, at the end of 2022, the number of movements still being below that of pre-pandemic times [7]. Gudmundsson expects that it will require up to five to ten years to recover to 2019 numbers of air traffic movements [8]. The dramatic reduction in flights is not only considered as negative. On the contrary, it could be seen as an opportunity to rebuild the system and make the air traffic sector greener than before the pandemic. In this context, Brouder and Ateljevic described the extensive economic reset evoked by COVID-19 but also the possibility for a fresh start [9,10]. From a general perspective, the air traffic in Europe was growing until 2019 and is expected to continue increasing significantly in the future again in order to cope with the growing demand for mobility and connectivity [11]. For example, Dube and Gössling assessed the rapid impact of pandemic control measures on the air transport sectors and the prospects for recovery of the global aviation industry [11,12].

**Citation:** Ahrenhold, N.; Stasicka, I.; Abdellaoui, R.; Mühlhausen, T.; Temme, M.-M. Enabling Green Approaches by FMS-AMAN Coordination. *Aerospace* **2023**, *10*, 278. https://doi.org/10.3390/ aerospace10030278

Academic Editors: Spiros Pantelakis, Andreas Strohmayer and Jordi Pons-Prats

Received: 2 February 2023 Revised: 8 March 2023 Accepted: 9 March 2023 Published: 11 March 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

The long-term effects on the environment from the aviation sector, mainly caused by aircraft noise and exhaust gases (especially CO2, nitrogen oxides NOx and methane), make aviation's environmental footprint a clear target for mitigation efforts. The future growth of air traffic shall go hand in hand with environmentally sustainability policies. Therefore, studies and research are being conducted especially in Europe, exploring possible optimisation of aircraft technologies and air traffic management (ATM) operations. This is investigated by Boli´c and Ravenhill within the Single European Sky ATM Research (SESAR) projects [13]. One possible starting point is the optimisation of ground movements at the airport. Within the EPISODE 3 project [14] and the EMMA project [15,16], advanced surface movement guidance systems were developed to design airport movements more efficiently. Furthermore, the use, optimisation and practical implementation of 4D trajectories, including a time parameter, was investigated by [17]. Given the close interdependence between aircraft routing and the resulting impact on the environment, optimisation of flight trajectory design and air traffic control (ATC) operations are appropriate means of reducing emissions in short and medium-term periods. Another target is the analysis of airspace conditions to mitigate delays due to overload. Analysing the air traffic complexity in the approach phase can lead to multi-sector planning operations, which detect overload and reduce delays. The Harmonised ATM Research in Eurocontrol (PHARE) [18] developed a algorithm to calculate the air traffic complexity.

Within the European funded project GreAT (Greener Air Traffic Operations), this paper investigates a new concept for the approach phase with a slightly extended scheduling horizon from 50 to 125 Nautical miles (NM) [19]. The main goal is to enable more sustainable approach procedures in terms of fuel-optimised approaches. This is realised by a new coordination system between aircraft flight management systems (FMSs) and arrival manager (AMAN) for guidance of inbound traffic. For that purpose, a new airspace structure and controller system enhancements for arrival and departure management are investigated within this project. In the following sections, all new concept elements are briefly introduced. In addition, the discrepancy between time-based and currently used distance-based planning is examined. These concept elements and the tactical assisting systems are the basis for the final human-in-the-loop (HITL) validation trials. According to EUROCONTROL's European Operational Concept Validation Methodology (E-OCVM), HITL simulations are appropriate techniques to receive objective and subjective outputs [20]. These outputs are generated by collecting data from simulator logs, observer notes, questionnaires and debriefings. The described study aims to test the system and concept improvements based on the advanced ATM procedures. Furthermore, the aim is to assess the reduction in fuel consumption by operational parameters and therefore, assess the reduction in greenhouse gas emissions too. Aside from the operational parameters directly linked to environmental sustainability, such as flown distance and number of landed aircraft, the air traffic controllers' (ATCOs) mental workload, situation awareness and perceived safety are analysed.

The concept of mental workload is described by Eggemeier and O'Donnell in [21]. An ATCO's mental workload is related to the requirements of the control tasks performed. As a new airspace design was proposed within the GreAT Project, it is important to assess if the ATCOs can handle the traffic within the new airspace structure while maintaining an acceptable level of mental workload. On the one hand, an unknown simulated operational environment with unfamiliar tools, including the radar display and new functionalities in the controller working position (CWP), may induce an additional workload. The extent of the increase will depend on the complexity and measures required to handle the new functions. On the other hand, an automated process of the 4D-FMS aircraft could also cause mental underload. It is furthermore essential that the ATCOs perceive operations as safe and that they maintain an adequate level of situation awareness. According to Endsley [22], situation awareness involves (a) the perception of the elements in the environment, (b) the comprehension of the current situation and (c) the projection of the future status.

For a medium–large-scale airport, such as Munich airport (EDDM), it is assumed that fuel-optimised procedures are not feasible due to the current airspace structure, average traffic flows and applied planning horizon. This hypothesis is underlined by two crucial reasons. Firstly, current AMANs are developed with regard to increased capacity and to support ATCOs at scheduling and sequencing of inbound traffic. Thus, the AMAN's planning process is not optimised towards fuel-efficient trajectories, rather than optimising the capacity. Enabling greener approaches at medium to large sized airports with less CO2 emissions, such as long-distance independent approaches, depends upon a redesign of the airspace structure and extension of the capacity-centred AMAN calculation. Since these independent long-distance approach procedures start at the top of decent and end on the final decent, aircraft's speed profiles are unknown for ATCOs, which requires more space for coordination with standard approaches [23]. Therefore, a completely new terminal manoeuvring area (TMA), a so-called the extended-TMA (E-TMA), was designed for the independent parallel runway system of EDDM. Additionally, a trajectory negotiation process between the aircraft's FMS and the in-house developed AMAN was established to enable long-distance independent approach procedures. Lastly, tactical supporting tools have been developed and provided for ATCOs to enable a time-based aircraft guidance system instead of the conventional distance-based guidance system, since the guidance of fuel-optimised approach routes follows the time principle in order to meet the negotiated target times, although occasionally, aircraft deviate from their optimum profiles. In the following, each concept will be introduced one after another.
