DB,
Thanks for the thread and a very pertinent discussion. We are grappling with exactly this issue at the bottom of the world right now. One option we are considering / trialling is a constant groundspeed approach. The (hoped for) advantage is two-fold:
1. Constant ground speed means (on a given night), constant IAS, which means constant pitch attitude. I.e. the sight picture is fixed in the windshield. All that remains is for the pilot to hold the same glidepath with collective until reaching that point of full visual cues where the final transition to the hover is made.
2. Constant ground-speed means ROD is always the same for a given approach angle.
We are trialling 30 kts, with a commence descent at 500 feet, 1.0 nm. Sounds a little flat but actually is not too bad. Our aim point (target height) is 50 feet above the deck, and you do the math from there (ROD is about 200 fpm). I've flown it in nil wind which is probably the most difficult, and the helicopter is nice and stable and the approach easy to control. As wind increases, it gets easier.
The big problem I see with the classic decelerative approach is that everything is changing on that approach. The airspeed is decreasing (which requires a steady increase in pitch attitude so your visual cue is moving); power required increases, so collective input is necessary. This gives flapback so cyclic correction is required. The whole approach is very dynamic (aka unstable!), which is possibly why it is very difficult to make a good job of it first time up for a couple of months.
Be interested in feedback on this concept.
Cheers