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Until NPAs are designed to provide obstacle clearance based on VNAV tolerances, any published altitude limitations must continue to be observed. Provided all such requirements are monitored and met, a VNAV system may be used to assist in flying a stabilized approach.
2.9 CAN I FLY AN RNAV APPROACH?
Yes. At present the only Area Navigation (RNAV) instrument approach procedures available in Australia are based on GPS. These procedures, commonly referred to as a GPS/NPA, from 25th November 2004 will be identified on approach charts as RNAV(GNSS) approaches. Aircraft equipped with TSO C129a or other approved GNSS systems may conduct RNAV(GNSS) approaches. Not all aircraft fitted with GPS (including FMC equipped aircraft) are approved for approach operations and pilots should determine the operational approvals applicable to each aircraft type.
Although many aircraft fitted with modern Flight Management Computer (FMC) systems have the capability to fly other approach procedures using RNAV, including procedures based on conventional navigation aids, the use of RNAV in place of the ground-based aid is not approved in Australia.
An RNAV system may also be used to assist in flying a conventional approach. However, it is necessary for the navigation system upon which the procedure is based to be monitored (NDB, VOR, etc) to ensure that the obstacle clearance requirements of the approach are met, and that the procedure is flown within the tolerances of the navigation system on which the procedure is based.
3.1 WHAT IS A STRAIGHT-IN APPROACH ?
A non-precision approach that is aligned with a suitable runway may permit an aircraft that becomes visual at or above the MDA to continue descent and land “straight-in”. This is commonly referred to as a straight-in or runway approach.
Approaches where the final approach course is not suitably aligned with a landing runway, or where the runway does not meet the required standard, will terminate at a circling MDA from which some manoeuvring is normally required before the aircraft can conduct further descent.
A straight-in approach is identified by the use of the runway direction in the title, e.g. RWY 14 NDB, and may be also be annotated in the minima box. e.g. by the letters S-I (straight-in).
Note: Refer also to special procedures applying to helicopter approaches in Section 7.
3. Straight-in approaches
3.2 WHAT ARE THE ADVANTAGES OF A STRAIGHT-IN APPROACH?
It is commonly acknowledged that runway approaches are much safer than circling approaches. In Australia, instrument approach procedures are designed as straight-in approaches wherever possible.
3.3 WHY AREN’T ALL APPROACHES STRAIGHT-IN APPROACHES?
In order for the aircraft to be able to safely land straight-in, the pilot needs to be able, at or before reaching the MDA, to sight the runway, align the aircraft with the centerline, and continue descent without significant changes to the descent rate, while visually avoiding any terrain in the runway approach area. In many cases a straight-in approach also permits a lower MDA but this also limits the amount of time and distance available to the pilot to complete the visual segment of the approach.
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本文链接地址：非精密进近 Non-Precision Approaches Civil Aviation Advisory Publication October 2004 CAAP 178-1(1)(5)
