RW-1
In answer to your question concerning the problems of reducing A/S on night approaches it's quite simple really.(No I'm not being condescending, it really is simple).
Mostly it's down to reduced visual cues. By day there are plenty of these available both consciously and sub-consciously. Loss of depth perception. Peripheral movement cues that disappear, ground rush etc. These are what usually give you a fairly accurate impression of both closing speed and rate/angle of descent. As these are unavailable at night the tendency is often to maintain too high a ground-speed for a given height. Then as you perceive the LS disappearing down the front of the w/screen the automatic response is to use aft cyclic to reduce speed, in a vain attempt to maintain your sight picture and/or to lower the collective with the same aim. This obviously puts you perilously close to the Vortex Ring regime so is often discouraged by instructors!!
A useful technique that avoids this is to adopt that as taught in the military. e.g. 500'/50kts, 400'/40kts, 300'/30kts, etc. It works every time and unlike the solution offered by offshoreigor does not rely on knowing your precise range from the LS.
BTW hovering at 5k is something you get used to, ask any Army Gazelle pilot.
offshoreigor
There are Radalts that read up to 5k, believe me the AN/APN 198 for example.
Oh yes Lu, thanks for a very short if totally unhelpful reply.
