..... You will never observe a rad alt indication of less than 200 feet on a Class One ILS but - (my assertion) - you may see a rad alt indication MORE THAN 200 feet at DA. Therefore a rad alt (if you are blessed with one) is a good device for telling you where the ground is right now but a useless device when deciding where the DA/H is or where the ground is up ahead.
I agree that the validity of the rad alt indications will increase as you approach the threshold after DA/H but at that vital moment when DA/H is achieved the rad alt information is purely incidental as a dip in the terrain may mean that it shows 250 feet at DA/H rather than 200 feet..
This takes me back to my original post - the number in brackets is NOT the height indicated by the rad alt when DA/H is reached.
Thanks to all who have contributed - your posts have blown away some myths and some cobwebs and I am grateful for your expertise.
G.
