KJZI (Charleston Executive, S.C.) ILS RWY 9 DME Required

" wrote
You imply Sam that timing alone is how you determine the MAP. I say
it's not.
DME determines when you can go below MDA which would be at MAP not 3
minutes 12 seconds.

SAY WHAT!!! Let's take a look at the definition of MDA:

"A specified altitude referenced to sea level for a non-precision approach
below which descent must not be made until the required visual reference to
continue the approach to land has been established."

It's pretty clear that we're not supposed to go below the published MDA on
a non-precision approach, unless we can see enough to descend and land. The
MAP has nothing to do with it except that we can't continue the approach to
land after reaching the MAP.

It seems to me that everyone is missing the main point about "DME
Required" is that it is NOT required....normally, that is.

Since The name of the proceedure does not include "DME" as in LOC/DME,
timing is a perfectly acceptable method of determining the MAP for the LOC
approach.

In all cases where timing may not be used, the procedure must be annotated
“timing not authorized for defining MAPt.”

Note where "DME Required" does appear....in the note section about raising
the minimum DA/MDA when the local altimeter setting is not available. I
suspect that the answer to the OP's question is in here somewhere.

Recommended reading

http://www.faasafety.gov/gslac/ALC/l....aspx?id=17273

Some general copy and paste from the Instrument Flying Handbook....

APPROACH CHART NAMING CONVENTIONS
Individual NACO charts are identified on both the top and
the bottom of the page by their procedure name (based on
the NAVAIDs required for the final approach), runway
served, and airport location.

APPROACH CHART NOTES
The navigation equipment that is required to join and fly
an instrument approach procedure is indicated by the title
of the procedure and notes on the chart. Straight-in IAPs
are identified by the navigation system by providing the
final approach guidance and the runway with which the
approach is aligned (for example, VOR RWY 13).
Circling-only approaches are identified by the navigation
system by providing final approach guidance and a letter
(for example, VOR A). More than one navigation system
separated by a slant indicates that more than one type of
equipment must be used to execute the final approach (for
example, VOR/DME RWY 31). More than one navigation
system separated by the word “or” indicates either
type of equipment can be used to execute the final
approach (for example,VOR or GPS RWY 15).

When radar or other equipment is required
on portions of the procedure outside the final approach
segment, including the missed approach, a note is charted
in the notes box of the pilot briefing portion of the
approach chart (for example, RADAR REQUIRED or
DME REQUIRED).

On some nonprecision approaches, the MAP is given as
a fixed distance with an associated time from the FAF to
the MAP based on the groundspeed of the aircraft. A
table on the lower right hand side of the approach chart
shows the distance in NM from the FAF to the MAP and
the time it takes at specific groundspeeds, given in 30-
knot increments. Pilots must determine the approximate
groundspeed and time based on the approach speed and
true airspeed of their aircraft and the current winds along
the final approach course. A clock or stopwatch should
be started at the FAF of an approach requiring this
method.

When a missed approach is executed
prior to reaching the MAP, the pilot is required to continue
along the final approach course, at an altitude
above the DA, DH, or MDA, until reaching the MAP
before making any turns. If a turn is initiated prior to
the MAP, obstacle clearance is not guaranteed.

Bob Moore
ATP CFII
PanAm (retired)