I like the logic of your argument - I had come to the same conclusion; best to forget flying all the way down the beam (although it would be possible for a proportion of the final descent), the essence is only to establish the intercept, the initial descent path and hence the correct 'sight picture'.
There are pointers to the difficulties that could exist; for years we have been trying to provide a wave-off light (to avoid the problem of wrong-rig landings) - we could never find one with sufficient intensity that it would be noticed when the pilot had convinced himself that this was the correct rig.
Don't minimise the problem of power supply - this has to be an intrinsically safe device.
You cannot rely on the lights being dimmed on the rig - some platforms are the equivalent of small cities and the lighting is there for a reason; dimming will not happen and can't be relied upon - best to strive for intensity.
The siting would also be problematic as it would be masked if approaching from the Limited Obstacle Sector.
However:
It is probably time to revisit the basis for the ODAPI; the advent of powerful LED lighting has now probably changed the balance.
Finding the correct angle of approach just from the deck lights is not really that simple. As I indicated in an earlier post, when measured, the ones shown on the presentation were: 10 degrees for too low; 20 degreees; and 35 degrees for too high. So not as easy as it first appears!
An alternative solution (to establishing the point of final descent) would be with a waypoint on the GPS; this could be calculated geometrically using (say) a 6 degree angle, the centre of the helideck and the altitude on the final track to fix it.
Jim
Last edited by JimL; 5th Apr 2009 at 13:04.