GPS Question

"Mark Hansen" wrote in message
...
On 03/09/06 11:35, rps wrote:
I thought I understood this, but maybe not. GPS systems were certified
for approaches after I got my instrument ticket, so my knowledge is
more anecdotal than from actual training.

Can an approach-certified GPS be used to substitute for NDB and DME
during an approach (or even en route)? What if the approach says ADF
Required or DME Required? My understanding of the AIM is that you can
only use the GPS as a substitute when there is a published GPS overlay
for the approach.

(My question is about the legality and not about whether you'd be close
enough.)


The AIM has a section devoted to the use of GPS in lieu of ADF and DME,
which will answer your question, and much more ;-)

Go to section 1-1-19, and look for "Use of GPS in lieu of ADF and DME".

The short answer is yes, you can use GPS as a replacement for ADF and DME
unless the navigational station is the primary for the approach (which
could be true for ADF, but not DME).

So, if you're flying an NDB approach, you could not use the GPS as a
replacement for the NDB ground station.

However, if you're flying an approach that requires DME, or an NDB to
identify the OM, you can use the GPS to provide that information.


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

Except for flying an approach at the alternate:

Ref: AIM 1-1-19, paragraph f.1.(b)(8)
Restrictions

"For TSO-C129/129A users, any required alternate airport must still have an
approved instrument approach procedure other than GPS that is anticipated to
be operational and available at the estimated time of arrival, and which the
aircraft is equipped to fly. If the non-GPS approaches on which the pilot
must rely require DME or ADF, the aircraft must be equipped with DME or ADF
avionics as appropriate."