If the ALSF-2 has a SSALR embedded within it, then the result is a minimum of four circuits for all the steady burning lights of a combined SSALR/ALSF-2 system. The steady burning lights of a standalone ALSF-2 are on a minimum of two circuits.This two-circuit configuration is also used when a SSALR is embedded within an ALSF-2. Figure 1 in Appendix A shows an example of barrettes circuit interleaving for the steady burning lights of a standalone SSALR approach lighting system serving a 45 m wide precision runway. The steady burning lights of an SSALR system are on a minimum of two circuits, whether the SSALR is a standalone system or embedded within an ALSF-2 system.The most commonly used method is interleaving individual barrettes.The lights of the approach lighting threshold bar are always interleaved by alternating individual lights. Circuit interleaving can be accomplished by interleaving individual barrettes, which is interleaving the bars of lights at selected light “stations”, by interleaving individual lights within the barrettes, or by using a combination thereof. In order to maintain a basic visual pattern in the approach lighting system, the steady burning lights of ALSF-2 and/or SSALR systems are on separate interleaved circuits.The calculation takes into consideration the lamp load, lamp tolerances, AGL transformer efficiencies, secondary cable losses, primary cable losses and feeder cable losses. Note: Regardless of the type of interleaving method chosen, calculation of circuit loading is required to optimize load balance and remain within limits. See Chapter 9 of TP312 for further details. Note: Continued operation of an approach lighting system with a failed circuit is not acceptable as this would result in exceeding the maximum number of light outages. This is to ensure the shape or pattern of the visual cues remains relevant enough to the pilot in that critical phase of flight. The objective of interleaving the lights of ALSF-2 and/or SSALR systems stems from the need to maintain visual guidance to a pilot in the final stage of a precision approach in the event that one circuit inadvertently fails. Note: For the latest version of that standard, see TP312, 5th edition Since 1990, TP312 states that for a precision runway, the electrical circuits for the power supply, lighting and control of the lighting systems shall be so designed that the failure of one circuit will not leave the pilot without visual guidance nor will it result in a misleading pattern. The absence of technical information on circuit interleaving for SSALR and ALSF-2 approach lighting systems may have led to improper circuit designs, which could therefore result in non-compliance. ICAO: International Civil Aviation Organization.RAIL: Runway Alignment Indicator Lights.ALSF-2: Approach Lighting System with Flashing lights for category II or III operations.SSALR: Simplified Short Approach Lighting System.The following abbreviations are used in this document:.By default, it is understood that the publication of a new issue of a document automatically renders any earlier issues of the same document null and void, unless an earlier issue remains valid under coming into force provision by regulation.Transport Canada Publication, TP312 – Aerodrome Standards and Recommended Practices.It is intended that the following reference materials be used in conjunction with this document:.This information is also available to the aviation industry for information purposes.Ģ.0 References and Requirements 2.1 Reference Documents This document applies to all aerodrome operators using a precision runway.This AC discusses circuit interleaving design of SSALR and ALSF-2 approach lighting systems for precision runways with respect to the standard in TP312 – Aerodrome Standards and Recommended Practices.This AC on its own does not change, create, amend or allow deviations from regulatory requirements, nor does it set up standards. It may describe an example of an acceptable means, but not the only means, of demonstrating compliance with regulations and standards. This Advisory Circular (AC) is provided for information and guidance purposes as a result of numerous queries from stakeholders looking for guidance on the application of the standard.Interleaving - ALSF-2 Approach Lighting System With Embedded SSALR Interleaving - SSALR Approach Lighting System Appendix A - Examples of Interleaving Circuits for SSALR/ALSF-2.ALSF-2/SSALR Circuit Interleaving Issuing Office:
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