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4.1 WHEN IS A CIRCLING APPROACH PUBLISHED?
A circling MDA will normally be shown for a straight-in approach procedure to permit circling to other runways, however where all the requirements for a runway approach cannot be met, only a circling approach is published.  
In some cases, although the final approach course may be runway-aligned, other factors will preclude the authorisation of a straight-in approach. Those factors may include:
. Final approach course not within the alignment criteria

. Final approach gradient too steep

. Obstacles above the 3.33% OLS

. Runway not surveyed to the required standard

. Aerodrome status.  (Certified and registered aerodromes are operated under rules that require regular safety inspections, reporting of aerodrome serviceability/status, and the monitoring of obstacles.)

4.2 HOW ARE CIRCLING ONLY APPROACHES IDENTIFIED?
An NPA that only provides for a circling procedure is identified in the title by reference to the navigation system only.  (e.g. NDB) Where more than one circling approach procedure is published at an aerodrome, the procedures title includes a suffix using letters from the beginning of the alphabet. e.g. NDB A, VOR B. 
For RNAV procedures the suffix may also be used to indicate the direction of the final leg to aid in pilot orientation.  For example, RNAV(GNSS) E indicates an approach from an easterly direction.   The letters N, S, E, and W are used as the suffix in these cases.
4.3  VISUAL LEGS
In rare cases a procedure may specify descent to a position outside the circling area, and require that a visual leg be flown from that position to establish the aircraft within the circling area.  In such cases obstacle clearance on the visual leg is the responsibility of the pilot and the visual leg must be flown clear of cloud and in sight of ground or water in conditions meeting specified altitude and visibility.
4.  Circling approaches

5.1 IS A GPS OR DME ARRIVAL AN NPA?
Yes.  A DME or GPS arrival is a procedure unique to Australia that provides a non-precision approach to a circling minimum.  A DME or GPS arrival is designed using the same criteria as used in conventional NPA design.
5.2 WHAT IS DIFFERENT ABOUT A DME OR GPS ARRIVAL?
DME or GPS arrivals are normally designed to permit descent from the en-route phase without the need to locate the aircraft overhead the navigation aid or conduct a sector entry.  Entry to the procedure is often available from any direction but commonly is limited to sectors or specific tracks.  Where sectors are promulgated, an aircraft can be manoeuvred to intercept any particular track, provided this is done prior to reaching the Final Approach Fix (FAF).  This procedure enables an arriving aircraft to be positioned on a convenient track for subsequent circuit entry or a straight-in approach, but prior to reaching the FAF the aircraft must be established on the final approach course and from the FAF the aircraft speed must be established within the range of speeds specified for the final leg.
　
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本文鏈接地址：非精密進近 Non-Precision Approaches Civil Aviation Advisory Publication October 2004 CAAP 178-1(1)(8)