ICASC_Paper_on_Flight_inspection_Intervals_IFIS_template_issue_1doc.doc

Flight testing instrumentation varies greatly only a

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flight testing instrumentation varies greatly, only a general description of the test methodology is given below . 4.3.2 Flight tests constitute in-flight evaluation and sampling of the radiated signals in the static operating environment. The signals-in-space are evaluated under the same conditions as they are presented to an aircraft, receiving system and after being influenced by factors external to the installation, e.g. site conditions, ground conductivity, terrain irregularities, metallic structures, propagation effects, etc. Because dynamic conditions, such as multipath due to taxiing or overflying aircraft or moving ground vehicles, are continually changing, they cannot be realistically flight-tested. Instead, these effects on the signal-in-space are controlled by the establishment of critical
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and sensitive areas and by operational controls”. So in summary flight inspection ensures that the Navigational Aid Signals in Space remain within the ICAO stated tolerances. There are two main contributions that can affect the signals in space, namely: Stability of the equipment Changes in the operating environment Financial Constraints Financial factors are often considered as part of the flight inspection extension process, it is essential that the final decision is made on a technical basis and that the safety of the service is not impacted. It should be recognised that over time a facility may become less stable and need to revert to a more frequent flight inspection interval. History of Changes in Doc 8071 ICAO Doc 8071 Volume II ILS (Instrument Landing System) 3rd edition issued in 1972 [2] stated the periodic interval for ILS as 90 days extending to 120 days for those facilities which have a history of good performance. No guidance was provided in the 3rd Edition to judge what constitutes good performance. A tolerance of +/- 15 days was allowed for routine inspections and +/- 60 days for the annual inspection. The 4th edition [1] included some significant changes: 1. Increase in the nominal flight inspection interval to 180 days. 2. Guidance on the factors to consider when extending the inspection interval. 3. Removal of the due date window for the inspection interval. According to one member of the Testing of Radio Navigation Study Group (TRNSG) present during the drafting stages of the 4th Edition, the group had to consider the interval standard under a consensus-setting environment. There were several constraints that had to be considered for example: Doc 8071 is used by some states as a contractual Statement - Many States were concerned that they should not make substantial changes; otherwise their contracts may need to be renegotiated, perhaps at higher costs. Technology advances - Solid state equipment and microprocessors where in common use, however, some States still had a significant proportion of thermionic tube equipment.
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