Reg C Elley:
Although your Altitude vs Airspeed analogy may work on a good visual night, it does not provide the necessary safe VTOSS (most twin helicopters are 35-45 kts) nor does it give you a very good margin above translational speed, (25-35 kts on most helicopters).
The "by the numbers" approach is designed for offshore approaches to a black hole, based on Radar distancing and provide a sfe flight profile with regards to VTOSS.
If used to an onshore facility, then it is only relevent when the distance back is known, however the approach speed must remain above translational speed at night regardless of distance back so as to avoid an inadvertant OGE hover at an unacceptable altitude.
Unlike the Military, Civil night ops are predicated on a known approach gate. I also know that in the Military, outside of a combat situation, you would not be expected to transition into an unrecenoitered area. At least that was the case in the CF.
Ofcourse if you are equipped with a Night Sun, then it becomes an entirely different story.
My point is, that if you are doing your night approach to a "Rig" type environment or to a "Known" land based helipad, such as a Hospital Pad or established night pad, then the "by the numbers" approach has been proven to be the safest and most effective in eliminating the guess work.
Cheers, OffshoreIgor
[This message has been edited by offshoreigor (edited 05 January 2001).]