Abstract -Multiple remote tower operations are one concept for more cost efficient air traffic control at smaller airports. One air traffic controller (ATCO) should control traffic at two or more airports at the same time. Multiple remote tower operations for two small airports has already been successfully been validated by LFV, the Swedish air navigation service provider. As monitoring and visual observation is an important task of tower controllers, this concept raises questions on how to best support human performance when it should be applied in high traffic environments. A high fidelity study with 16 ATCOs investigated into the influence of multiple remote operations on visual attention and monitoring performance. The study was set up with high traffic volumes putting a maximum workload on the ATCO for a whole simulation run. Empirical results of eye movement measures are presented. Whilst in general visual attention distribution was not affected, less relevant events were monitored, because the visual attention was distributed over the two airports. In order to mitigate these effects, two workplace design approaches are presented -information integration and attention guidance. Advantages and challenges of the two approaches are discussed, with a focus on the impact of the design concepts on the working methods of air traffic controllers. Keywords -multiple remote tower, visual attention, workplace design, interaction design, human factors, eye tracking There are numerous airports in the world with rather little air traffic, compared to the big hubs like Frankfurt, London or Chicago. Nevertheless, by law, air navigation service providers have to provide expensive services to these airports. The concept of remote tower was developed as a solution for smaller airports with little traffic. The traditional tower is replaced by video cameras, the video data is streamed to a workplace and reconstructed as a video-panorama [1] . Typically, these airports have a simple layout and have almost no additional ground based sensors. The multiple remote tower concept is the next step. Multiple remote tower control aims at enabling one air traffic controller (ATCO) to control simultaneous traffic at two or more airports at the same time. The advantage of the concept is that ATCOs workforce is used in a more flexible manner. While the concept has proven to be feasible for two small airports already, the concept raises questions on how to best support human performance when the concept should be applied in high traffic environments. A major bottleneck is seen in the allocation of visual attention of the ATCO for monitoring the traffic at multiple airports. In 2010, a first study already addressed the feasibility of controlling two airports in parallel, with a special focus on the visual attention of the ATCOs, the workplace design, and its influence on the control task [2] . First results indicate that there is not a general limitation in the human's cognition that eliminates the concept. Nevertheless, a simple thought experiment would lead to the result that the probability to detect information is halved if the number of displays is doubled that an ATCO has to monitor. It is likely that monitoring is influenced by the multiple concept but it is unclear, to which extent and how the influence can be mitigated. The motivation of this work is to understand, in which way new design concepts can help to enable a new concept like multiple remote tower. There are several parameters that could be adjusted to make multiple remote tower feasible. For instance, mechanisms of the traffic flowmanagement could be used to ensure that there is limited parallel traffic at the airports controlled by a single ATCO. Procedures at these airports could be adopted, to avoid unforeseen traffic peaks and thus minimize peaks in the ATCOs taskload. We see significant potential in the parameter workplace design. Therefore, this paper is focusing on the environment in which the ATCO is performing air traffic control tasks. II. BACKGROUND & THEORY Controllers Air Traffic Controllers are responsible for the safety and efficiency of the air traffic. According to the different phases of a flight, there are different working profiles of air traffic controllers. At an airport, tower air traffic controllers manage the arrivals and departures to ensure safe landings, take-offs and taxiing on ground. Their main task is to create a safe and efficient traffic flow. Therefore, the monitoring of traffic, especially on the runway and within the control zone is an important safety mechanism. Thus, observation and visual attention resources of the controller are crucial parameters for the ATCOs working positon. Up to now, the ATCOs heavily depend on visual observation conducted through the windows of the airport tower (out of the tower view, OTW). The empirical data reported in this paper was generated within the framework of SESAR 06.08.04. About SESAR & SESAR JU: As the technological pillar of the Single European Sky initiative, SESAR aims to modernise and harmonise air traffic management in Europe. The SESAR Joint Undertaking (SESAR JU) was established in 2007 as a public-private partnership to support this endeavour. It does so by pooling the knowledge and resources of the entire ATM community in order to define, research, develop and validate innovative technological and operational solutions. The SESAR JU is also responsible for the execution of the European ATM Master Plan. Founded by the European Union and Eurocontrol, the SESAR JU has 19 members, who together with their partners and affiliate associations will represent over 100 companies working in Europe and beyond. The SESAR JU also works closely with staff associations, regulators, airport operators and the scientific community. Find out more: www.sesarju.eu 978-1-5090-2523-7/16/$31.00 ©2016 IEEE 1 Air traffic control is a complex, and mainly cognitive task, so perception of information, processing of information and decision making are important sub-tasks. In their task and job analysis of the different air traffic controller working position, Dittmann and colleagues defined a set of basic cognitive processes, describing the ATCO task. These are: managing routine traffic, issuing instructions, managing requests, solving conflicts, taking over position, monitoring, updating the mental picture, searching conflicts, general information processing and switching attention [3] . The cognitive processes monitoring, updating the mental picture and switching attention are of special interest in this paper and will be described in detail in the following chapters. We begin by describing an ATCO workplace. Besides the OTW, the workplace of an ATCO consists of multiple sources of information, presented via displays that need to be monitored, checked and integrated into the mental picture. According to results of a controller survey, the six most important sources of information are (in descending order) radio communication, OTW, approach radar, direct communication with colleagues (elbow coordination), the flight strips and ground radio [4] . In this paper we focus on OTW, approach radar and flight strips, because their information is presented visually within the workplace. The approach radar shows the position, height and speed of aircraft, as well as secondary data. The flight strips are used to keep track of the instructions given to pilots, to preplan the traffic and to support the mental traffic picture. The information sources radio communication, approach radar and OTW are used as three independent information sources, e.g. to verify the position of an aircraft. The OTW is further used to check the status of the runway and is the primary visual information source. The following section, thus, is focusing in detail on the role and importance of the monitoring task and the OTW. Results of an analysis of critical situations experienced by tower controllers show that in most situations the OTW provided the relevant information used for decision making. Especially, abnormalities were discovered and anticipated by information from the OTW, and the information of the OTW was used to compose and verify the mental traffic picture [4] . ATCOs are supposed to build a "mental traffic picture" of the traffic to anticipate the traffic development and take according actions to guarantee a safe and efficient traffic flow [5] . Controllers characterize their working style, when they "have the mental picture" as working ahead of the traffic. In contrast, when they lose the picture, the working style is characterized as starting to "swim" and to "work behind" the traffic. A conceptual idea and visualization of the mental traffic picture in the tower domain is given by Möhlenbrink et al. [6] , which emphasizes the high pace of events and triggers at the airport environment that force ATCOs to reorganize their plan and strategies for handling the traffic. As a consequence, it can be stated that ATCOs should always be able to detect any deviation from their preplanned mental picture as quick as possible to reorganize their plan for handling the traffic. The OTW can provide crucial triggers and ATCOs should monitor the OTW as often as possible. This is especially valid for the smaller airports, with no sensor equipment like A-SMGCS or ground radar and a higher rate of traffic following visual flight rules (VFR). Research confirms the importance of the OTW for the monitoring task of ATCOs. Research on visual aspects of tower operations analyzed the perceived importance of visual observation for different flight phases under responsibility of the tower ATCO [7] . Even though the results indicate that not all decisions are solely based on visual observation, the OTW provides cues that the ATCOs indirectly use for their decision making. These findings were confirmed by the results of a high-fidelity simulation study. The eye-gaze profiles of participants indicated that the most often used information sources (for visual information) were the "out-of-the tower view", followed by the approach radar and the flight strips. [8] Tower controllers monitor multiple visual information sources. The OTW is a rich information source for the detection of unexpected events that influence the preplanned traffic flow. The decision, where to locate attention to, also described as switching of attention, is therefore an important cognitive process. Especially, the theories and concepts relevant for control of visual attention in a multiple remote tower environment are pointed out in the following sections. In the cognitive theory, visual attention is one part of the human information processing scheme. For instance, Wickens defines visual attention as a cognitive resource that is limited and that can be consciously allocated to certain processes, where it is needed [9] . The characteristics of visual attention relate strongly to the physiological parameters of the human eye. Visual attention is likely correlated with saccadic eye movement. In visual search tasks, the point the operator is fixating on a display relates to the focus of visual attention. Furthermore, there is an area around the center of a fixation, which is used for information extraction [9] . Following, the focus of the eye gaze is interpreted as the focus of the attention. Information in the focal view is consciously processed. Additionally, information in the peripheral view can also be perceived, processed and used for decisions in case it is sufficiently salient. The combined area of foveal and peripheral is also described as the primary visual area of a workplace, where information can be accessed without additional head movements. As a design guideline, the most relevant information should be in this primary visual area. Already now, the layout of the conventional tower controller working position, and the size of all the displays required, does not allow to place all relevant information into the primary visual area. Based on this, the ATCO can't monitor all information sources at the same time but has to sequentially allocate visual attention to the most relevant information sources. The relevance of information is dependent on the task and the situation, which makes a decision on a certain design more complex.  One potential problem of allocation of visual attention and its operational impact can be summarized as the "head-up" and "head-down" problematic. Head-down times of ATCOs at an airport relate to those times, the ATCO is not looking outside the window but on any other display [10] . The monitoring of the OTW at the remote tower working position thus is described as working "head-up". From an operational point of view, the head-down times should be minimized, because the tower ATCO is expected to react as quickly as possible to any unforeseen event. These unforeseen events are most likely to be detected by visual surveillance, looking either outside the tower windows or on a panorama video presentation. Head-Down times occur when the ATCO uses the preprocessed, high-quality, focused information of assistance tools, for instance the flight strips, approach radar or the map. In modern towers at more frequented airports, head-down times may occur through the use of management tools, e.g. a departure manager or other information systems representing the status of the airport. As explained, switching the attention to the different information sources is a mechanism to not oversee an important event. Within the cognitive theory, two mechanisms for the guidance of visual attention are distinguished -bottomup and top-down processes. The terms of bottom and top refer to hierarchical models of human information processing in the brain, from a stimulus to brain areas and centers that are involved in certain cognitive tasks. The term bottom-up refers to lower levels of stimulus, for instance on basis of signals on the eye nerve. Top-Down refers to the idea that higher centers and functions are involved, like "understanding" and "sensemaking" [9] . Top-Down can be described as the visual attention is guided by expectations. Top down guidance of attention is conducted via interpretation of stimulus, knowledge gained through experience and thus expectations, what is going to happen where. For instance, because of the knowledge that an aircraft has reported being on the final, the ATCO expects to see the landing lights in the according area of the OTW. Thus, the visual attention was guided by top-down processes. Furthermore, the knowledge that aircraft do switch their landing lights on leads to the expectation that the ATCO watches out for a bright light. Bottom-Up guidance occurs by lower level stimulus like contrast, acuity and size of a target. For instance, the flashing light of the fire brigade catches the attention due to large differences in contrast, which is seen as a blinking. A rapidly moving object causes a bottom-up stimulus and is also likely to gain visual attention. In search tasks the visual attention is typically driven by top-down processes, and occasionally by salient bottom-up processes [9] . For the air traffic control domain, Kallus et al. created cognitive profiles of the different air-traffic controller positions. They found out that typically tower controller subtask are both bottom-up and top-down driven. But for the sub process searching and solving conflicts, the tower control is more bottom-up driven compared to the approach and enroute domain [3] . By implementing a multiple remote tower, ATCO's workforce can be used in a more flexible manner. The concept raises questions on how to best support human performance when the concept should be applied in high traffic environments. A major bottleneck is the visual attention of ATCOs for monitoring the traffic at the two airports. As an example, it is a normative behavior that the controller should monitor an aircraft during the take-off and landing phase to detect any hazardous events as early as possible. It is of interest to understand, in how far the monitoring performance of the ATCO is influenced by introducing the multiple remote tower concept. More precisely, it is of interest whether the ATCO is able to monitor as many take-off and landings as when working on a conventional tower. As a strong influence of the concept on visual attention is expected, the second research question is, by which new design approaches the impact of the multiple remote tower concept can be mitigated, based on the results of the empirical results.
A first study was published in 2010 to demonstrate the feasibility of multiple RT, at least to control two small airports simultaneously (Moehlenbrink and Pa-penfuss, 2011; REF .
Head up only — A design concept to enable multiple remote tower operations
2016 IEEE/AIAA 35th Digital Avionics Systems Conference (DASC)
2016 IEEE/AIAA 35th Digital Avionics Systems Conference (DASC)
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