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Old March 18th 10, 03:58 PM posted to rec.aviation.ifr
Sam Spade
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Posts: 1,326
Default KJZI (Charleston Executive, S.C.) ILS RWY 9 DME Required

Padraig wrote:
Bob, sorry, substitute TDZ with MAP. My point is that generally a VDP
is measured from the end of the runway (beginning of TDZ) which is
often where the MAP is (on RNAV approaches).


Not exactly correct:

(1) For runways served by a VGSI (regardless of coincidence with final
VDA) , using the VGSI TCH, establish the distance from RWT coordinates
to a point where the lowest published VGSI glidepath angle reaches the
appropriate MDA.

(2) For runways NOT served by a VGSI, using an appropriate TCH from Vol.
3, chapter 2, table 2-3, establish the distance from RWT coordinates to
a point where the greater of a three degree or the final segment VDA
reaches the appropriate MDA.

My point is that a VDP has a threshold crossing height (TCH) as do all
vertically guided IAPs.

As to the MAP being at the approach end of the runway (AER), that is
correct only for NPAs whether LNAV, VOR, NDB, or LOC/LDA. The NPA MAP
will be prior to the AER when obstacles in the missed approach segment
preclude siting it at the AER.

Vertically guided approaches (with a DA/DH) always have their MAP at DA/DH.