Are you aware of any A320 that doesn't have this V/S button additional function?
All FBW Airbus have this feature. What is not common is the expedite button, that is an "ALT" button on a lot of aircraft.
Originally Posted by RAT 5
I remember an old edict that a circling approach was any approach where the approach track was >30 degrees from runway centreline. Thus, once within 30 degrees you were no longer circling and descent was at pilot discretion.
There is no ICAO requirement to be within 30 degrees in order to descent below the circling MDA. The requirement is to maintain visual reference with the runway environment. There are a lot of circling approaches which puts an aircraft on an oblique base position where they can maintain visual reference with the runway environment.
The 30 degrees came from the final approach alignment criteria for straight in approaches in Cat A&B to be within 30 degrees of the centreline, and 15 degrees otherwise.
From PAN-OPS
5.2.2.3.1 Maximum angle. For a straight-in approach, the angle formed by the final approach track and the runway centre line shall not exceed:
a) 30° for procedures restricted to Cat A and B aircraft ; and
b) 15° for other aircraft categories.
These are some of the variations in industry that are widely used.
Only when visual contact can be maintained and on the middle of the base leg, never earlier.
• Within 30 degrees from the final approach track
• This depends on whether visual or have achieved circling criteria. This is
interpreted that you cannot descend below Circling Minima until you intercept
the nominal approach angle, or you declare visual – in the latter case the crew
become fully responsible for terrain avoidance.
• If the Circling minima are high (above 1500ft AAL - normal basic training
circuit altitude) some operators ask crews to ensure that the aircraft remain
within the protected area at all times. To achieve this it may mean descending
before the base turn is commenced to ensure a normal descent angle to
landing. Before leaving MDA certain criteria must be met. Ideally the RWY
environment should be visual at every stage of the descent but practically this
may not always be the case, particularly if the MDA is high or there is a
prescribed track associated with the circling manoeuvre. The really important
point is that we must assure ourselves that the predicted flight path of the
aircraft will remain in a clear area at all times with regard to both weather
and obstacles before a descent is commenced.
• The crew must maintain the MDA until the runway threshold has been
positively identified by the PF and that a normal FPA can be achieved to land
in the TDZ, a steep or a flat descent should not be attempted, if at any stage
the visual cues of the runway are lost, a missed approach should be initiated
• Generally, crew should stay at circling MDA/ H until necessary for approach
and landing; this is often on base leg. This is based on the height of MDA and
the interception of a normal glide path.
• Fly at circling minima (AP and AT engaged) all the way to the end of the
downwind leg and commence descent when turning bas.
• Landing threshold acquired by PF and the aircraft is in a position to carry out
a landing.
• It is important that the descent is to be made in a way to allow for a stabilized approach.
• Some operators require that the MDA be maintained until the aircraft has
manoeuvred to within a 30 degree angle of the extended runway centreline.
from
http://skybrary.aero/bookshelf/books/1486.pdf