On 03/14/06 08:51, Peter wrote:
"Steven P. McNicoll" wrote:

Right, GPS cannot substitute for ADF on this approach because ADF is the
principal instrument approach navigation source. For that same reason GPS
cannot substitute for DME on the VOR/DME or TACAN Z RWY 15 at MTN.

I am from Europe, where US-style GPS substitution for various navaids
is not permitted. So this is of academic interest only.

(With one small exception I know of, Switzerland, where (as is not
uncommon in Europe) an ADF is required for all controlled airspace
unless one carries a BRNAV approved GPS.)

Anyway, this thread has left me well confused. I've done the FAA IR
(at a U.S. school not using GPS so GPS questions didn't come up) so I
recall that any navaid shown on the approach plate can be substituted
for the OM, and only radar or an NDB (a "compass locator") can subst
for the middle marker.

I also recall that if an alternate is required (the destination not
meeting the 1/2/3 rule)

.... or if the destination doesn't have an instrument approach

and the only approach available at the
alternate is a GPS one, that airport cannot be filed as an
alternate.... or something like that. This requirement (which I
probably wrote wrongly) is what puzzles me regarding Cirrus (for
example) not being fitted with an ADF and a DME - doesn't it curtail
the alternate options considerably?

Not at all. There are a lot of ILS, VOR, etc. approaches which do not
require DME or ADF. Note that you do not need an ADF to make use of
the OM and MM - a marker beacon receiver is just fine.


Getting back to the more general substitution regs: on the *primary*
destination, is it OK to substitute a GPS for any navaid provided the
navaid is not used to provide the lateral guidance?

There is a section in the AIM which covers this question exactly. It
is called "Use of GPS in lieu of ADF and DME".

In this case, we're not talking about GPS approaches, but approaches
like ILS, VOR, NDB, etc. In these cases, the GPS can be used as a
substitute for the ADF and/or DME (in specific cases, as detailed
by the AIM). However, you would not be able to substitute the VOR
on a VOR approach, etc. For that, you need to fly the VOR (GPS)
or GPS approach.


--
Mark Hansen, PP-ASEL, Instrument Airplane
Cal Aggie Flying Farmers
Sacramento, CA