That is a great manual. But, I fail to see where anything in it answers
the OP's question.

Jeppesen adds computer navigation fixes (CNFs) to many non-RNAV IAPs to
tie the procedure togeter for RNAV navigation. CNFs are charted. The
fix at issue, the STW 16.5 DME is not charted as a CNF.

Other fixes that will be added are (such as) turn-on CNFs for DME ARC
interception, as a common example.

But, the STW 16.5 DME doesn't serve that purpose either. In fact, it
doesn't serve any navigation or continuity purposes that I can see. Do
you have some additional insight?

Tauno Voipio wrote:
Evan Salant wrote:

With the Garmin 430W (and presumably the 530 as well) when one flies
certain approaches the Garmin has you fly to fixes that appear nowhere
on the published approach plate. For example, if you fly the ILS24
approach at ABE from STW (Stillwater) IAF, the Garmin will have you
fly from STW to D16.5 then 4 miles to MUDRE intersection. The fix
"D16.5" appears nowhere on the published approach plate. Is there any
discussion of this anywhere ? Why does the Garmin seem to need a fix
4 miles outside of another IAF ?

Thanks.


Go to http://www.pplir.org, and get the RNAV tutorial manual.
It explains clearly how the extra points are named and why.

The whole document is recommended reading. The database coding
part begins on page 68.