On Sun, 10 Oct 2004 20:37:11 +0000 (UTC),
(Paul Tomblin) wrote:

I'm trying to figure out the BAF ILS 23 localizer approach. The normal
LOC 23 approach has a MDA of 900, and the LOC 23/DME approach has a MDA of
700 feet. After the FAF, there is a step down fix at 2.7 DME with a
_1160_ before it. So does this mean that if you don't have DME, you can
descend to 900 immediately after the FAF, but if you do have DME you can
only descend to 1160 until 2.7 DME? Why is it safe to descend to 900 in
one case, but only 1160 in the other?


I may be completely wrong on this, but I think the 1160 is a step down
for both types. As I see it if you have DME you can proceed lower (to
700) at the 2.7 mile mark, otherwise the radar facility will call the
2.7 mile position for you at which time you can proceed lower to 900.
This may allow for the radar facility to be more inaccurate than the
on board DME. The approach does say Radar Required.

Also, If you proceed to 700 you'll go missed at .9 DME, where as if
you don't have DME. all you have is time. I think they might also
want some added safety for some reason (possibly for clearance of the
390 foot obstacle right near the end of the runway).

There's also 923 foot obstacle just left of course after the FAF that
I'd be very careful to stay above, and is what made me initially think
the 1160 was for both approaches.

Hope this helps. Looking forward to further discussion on this one.

z