5.2.7.1 Visual presentation set-up and layout

The visual presentation should be designed to avoid unnecessary discontinuities or non-uniformities of the presented view. Existing discontinuities and non-uniformities should be clearly indicated so as to avoid misleading impressions of the observed area. For the case of seams/joints in the visual presentation, they should, as far as possible, be avoided at operational ‘hot spot’ areas such as holding positions, runway entrance/exits, etc. When this would not be achievable, mitigation measures should be considered, such as a hot spot camera providing an unobscured/unbroken view (or a predefined ‘quick access’ position for the binocular functionality). This recommendation can be seen as related to the guidelines provided in Chapter 2.1.4 of ICAO Doc 9426 [15], stating: ‘Vertical supports for the cab roof should be kept to the smallest feasible diameter so as to minimize their obstruction of the controller’s view. The supports should also be as few as possible…’. A difference with regard to the ‘vertical supports for the cab roof’ of a conventional tower compared to the frames/joints between cameras/screens in a visual presentation, is that the vertical supports are actually blocking the view, whereas the frames/joints in a visual presentation are probably not blocking any part of the view, but rather just separating the images. Even so, it is recommended to minimise the number of seams/joints (e.g. between screens) in the visual presentation, and if existing, to keep them to the smallest feasible width (e.g. by using screens with narrow frames/borders). Also, the risk of potential loss of information between images (e.g. when combining images from different sensors) should be thoroughly assessed as part of the implementation, and if such information loss can be detected, appropriate mitigation means should be introduced. A factor to take into account in this regard is the natural system degradation that may occur over time. For instance, even if there is no occurrence of information loss when the system is new and recently installed, weather and natural wear may affect the equipment and its configuration, resulting in a potential loss of information over time. If this is regarded as a potential risk factor for a particular implementation case, it is recommended that regular checks are introduced as part of the overall maintenance programme. In case a partial or full loss of visual presentation is expected to be mitigated utilising the binocular functionality, see considerations in the second to last paragraph in Section 5.2.7.2 below.