applied sciences Article  
A Vertiport Design Heuristic to Ensure Efficient Ground Operations for Urban Air Mobility  
[PERSON] 12,* 2 and [PERSON] 12,2  
Footnote 11: footnot  
however, the operations on the ground are not only unknown but also difficult to anticipate. Therefore, every effort must be made to understand vertiport operations in general and airfield operations in particular before UAM can take-off.  
Both vertiport Air Traffic Management (ATM) and general vertiport layout capacities have been studied to some extent, but (dynamics of) operations on the airfield have been neglected so far. For the vertiport ATM, the questions of arrival management and queuing of vehicles when the capacity limit is reached seems to be of special interest. Various strategies for approaching vehicles have been proposed such as concentric circles for holding loops [7], a rolling horizon to buffer the arrival time [8] or spiral-shaped approach and departure paths above the vertiport [9]. In addition the throughput of vertiports was analyzed in terms of vertiport capacities [10] and airfield topologies [11]. Though these are valuable first steps, the studies take a system-level approach and do not consider dynamics of vertiport airfield operations and in particular conflicts between individual participants of the operations. [PERSON] et al. was the first to simulate vertiport operations with a discrete-event modeling approach [12]. However the purpose of the study was the development of a vertiport airside concept of operations and was limited to one vertiport scenario. Further mention is due to [PERSON] et al. who also uses discrete-event simulation [13], yet the number of operations is limited to 325 per day and the scenarios, therefore, do not reach the expected complexity of operations. The sensitivities of vertiport operations and the dynamics of vertiport airfield operations remain unknown according to the current state of literature.  
This article wants to increase the level of understanding around vertiport design through agent-based simulation and identify and quantify the main drivers of operations. The main gap of understanding, as identified above, lies first with the vertiport airfield (airside-ground). Second, it lies with the operational dynamics including peaks in demand and conflicts between actors involved in the operations. This leads to the following research question:  
_Is it possible to predict the operational efficiency of a given vertiport based on limited knowledge of the proposed layout and expected demand?_  
The main contributions of this work are fourfold: (1) the main drivers of operational inefficiency (throughout this article measured as \"passenger delay\") will be identified. (2) By applying the concept of \"practical capacity\" borrowed from airport operations (see Section 3) the thresholds for efficient vertiport operations will be be quantified. (3) A variation of vertiport layouts and processes will be studied alongside varying demand to understand the impact of pad and gate operations (see Section 4). (4) The results of pad and gate studies will be aggregated into a graphical display to enable transfer of insights between a range of vertiport layouts and operational specifications (see Section 4.3). Thus, the above-stated research question will be answered through establishing a design heuristic, which captures all top-level drivers of vertiport operations.