blackboxman wrote:

Yeah, that's what's got me wondering -- there is a marker beacon, so
why the DME requirement? This approach didn't require DME when the
RITTS compass locator was there (I guess it's been or being
decommissioned). AIM 1-1-9 doesn't say that an ILS has to have both a
marker beacon AND DME or a compass locator.


My guess is the OM is a normal powered fan marker and the fix
displacement error is too large for it to serve as a FAF, so DME
is required.

For a fix to be satisfactory for use as a FAF, the fix displacement error
should not exceed 1 mile. It may be as large as 2 miles when the MAP
is marked by overheading an air navigation facility (except 75 MHz
markers), or a buffer of equal length to the excessive fix error is
provided between the published MAP and the point where the missed
approach surface begins. A normal powered fan marker has a fix
displacement error of two miles, a low powered fan marker has a fix
displacement error of 1/2 mile. DME also has a fix displacement error
of 1/2 mile.