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On Sat, 02 Mar 2002 00:27:09 GMT, "Doug" <anothername@earthlink.net> wrote:

>Someone mentioned that an ILS is good to 100' (if the MAP is 200'). Is this
>always true. Is a CAT III ILS good to touchdown? I realize I cant fly it
>legally down that far, but if the visibility is marginal, but within limits
>of the CAT I ILS, is it OK to follow the glideslope down further?
>
>

According to the AIM, a glideslope is good down to the lowest authorized
DH. Below DH it's indications must be supplemented by visual reference.

For a CATIII approach, with no published DH, the glide slope will be good
down to the runway.

The above is "what you can count on" if the weather is bad.

Now, I've flown a number of CAT I ILS's down to 100' (or lower) at various
locations and we seemed to be on the glide path -- no way to be certain
with the equipment in my a/c. And it may be that some of these are OK some
of the time.

But the approach zone is surveyed differently for CATII and CATIII
approaches -- including the effects of vehicles and other a/c in critical
areas. So you really can't be sure of guidance below DH.

Having said that, if it were an emergency, I would follow the GP down ...
at least you're going to land on the runway that way.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

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