Thread: GPS Question
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Old March 16th 06, 10:14 PM posted to rec.aviation.ifr
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Default GPS Question


"rps" wrote in message
ups.com...
Steven P. McNicoll wrote:
wrote in message
...

Now, please review with me my home airport... KFNL
http://www.myairplane.com/databases/...s/05677I33.PDF

Note in the lower left of the central graphic box, where it says
"ADF REQUIRED". In this case the GPS may be substituted for the
NDB, as this is an ILS approach and the NDB is not the primary
navaid.


Correct, ADF is needed for the missed approach procedure.


I (the person who started this thread) am confused again. Do I need an
ADF when I shoot this procedure, or not?

Some plates say "ADF Required." I think I've seen some plates say "DME
Required." Can I legally begin the approach in a Cirrus that has no
ADF or DME?


Yes, since the primary approach guidance is from the ILS and the NDB is
there to identify the marker and the missed approach holding fix. This is
an example of when the GPS can be used in lieu of the ADF at your
destination airport. But if GPS goes south during the approach and you have
to go missed...

The rule about when you can't use GPS in lieu of DME/ADF applies if you're
required to file an alternate. There must be another approach available at
the alternate that doesn't have a DME/ADF requirement. As I posted earlier,
this is to ensure you have a usable approach in the event of GPS failure.
For this ILS at FNL, you'd probably need radar vectors to guide you to the
marker if you had no GPS and no ADF. But what if you lost comm? Most of
the belt & suspenders safety rules for IFR ops are to give you an 'out' in
the case of lost comm or nav capability. Finding a non-DME or non-ADF
approach could take a bit of searching! But, as a previous poster noted, if
you have to go missed for a non-GPS reason, you can (in my opinion) still
use your GPS in lieu of DME/ADF where you need it. The bottom line is, use
everything you've got to protect your skin, your tin, and your ticket - in
that order.