For an NPA (namely Adelaide Australia 12 VOR) there are 2 MDA's published for a straight in approach. The lower MDA of 470ft requires a 3.6% gradient. The higher MDA of 780ft requires the standard 2.5%.
When flying a multi-engine aircraft (a light one, which will just achieve 2.5%, maybe a little more) which MDA should be used?
Arguments for the lower one; better chance of getting visual (especially in an actual engine failure scenario), there can be an 'escape route' if you need to conduct the missed approach and unable to achieve the gradient (whether an engine has failed prior to or during the missed approach, regardless).
Arguments for the higher; the gradient can't be achieved in the missed approach if an engine fails.... which leads on to another stance....
use the lower one if both engines are operating, the higher if asymmetric. (but what happens if one fails during the missed approach from the lower MDA and the 3.6% cannot be achieved?)
chart:
http://www.airservicesaustralia.com/...ADVO03-106.pdf
In some cases, if 2.5% cannot be achieved, there are ways to calculate how much to raise the MDA by to achieve obstacle separation up to the Missed approach altitude... I don't see why that principle would change in this case.
Any references to documents would be appreciated.
