This section presents the realization of this replacement project and its technical outcome. The site of the localizer 16 in Zurich has been identified as a potential site, where the coverage reduction may solve the signal in space problems. Thus, where operationally compatible, coverage could be raised at the limits of coverage (17NM), starting from 15 degrees and 2000ft HAT (Height Above Threshold), up to 4500ft HAT at 35 degrees, as illustrated by Figure 8. The proposal currently being discussed foresees to raise the lower boundary of coverage in line with operational requirements, up to a maximum lower boundary. Consequently, an alternate requirements formulation was pursued. This was primarily due to concerns over FM broadcast compatibility and possible further building development. Despite coverage requirements having been successively reduced over the many years of ILS operation (first from omni-directional to ☙0 degrees and then to the current ☓ 5 degrees), it proved difficult to implement a relaxation of field strength requirements down to ☑5 degrees. In order to encourage global implementation of this solution which increases the achievable safety margins, the work was presented both to the ICAO Navigations Systems Panel and the Operations Panel,. This confirmed that the intended goals were fully achieved, e.g., that the change in localizer design was completely unnoticeable by flight crews and ATC. This included feedback from flight crews, flight data analysis, as well as a detailed safety monitoring by the service provider operational staff. The validation work of the implementation in Zurich included a review of operational data. The ability of the new localizer to restore multipath margins in comparison to an existing solution is shown in Figure 7.
#LOCALIZER SERVICE VOLUME PLUS#
This has been evaluated at a major airport with a building reflector at 12 plus degrees through a dedicated site survey and simulation in order to address the clearance–course interference case. Simulations confirmed that a key benefit of the design was to increase signal quality by shifting the clearance peak away from 12 to 15 degrees to 7 to 8 degrees from the centerline. As a consequence of these operationally derived requirements, a new localizer design, as explained above, was undertaken. Despite this diverging operational reality, it was demonstrated through a task-load study that pilots would still be in a position to complete the IDENT check during a worst-case, high-workload intercept of a reduced coverage system. In fact, the IDENT turned out to be the most constraining function in relation to coverage requirements, as pilots have become used to completing the IDENT check as part of the check for approach, around flight level 100 – typically significantly outside of conventional coverage. This requirement had the secondary effect that IDENT coverage would also be ensured in line with operator’s expectations. Consequently, a “reduced coverage localizer” would need to maintain a clearance signal strong enough to cover any course sidelobes.
#LOCALIZER SERVICE VOLUME FREE#
Outside of 15 degrees, however, aircraft operators still expect the ILS signal to be free from low clearance or false course indications – out to the conventional 35 degree limits.
localizer intercept, even in worst-case scenarios.
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