More KAP 140 questions

"Peter R." wrote:

With my KLN94 I use the OBS mode for VOR approaches. Direct to the VOR
used in the approach, then OBS mode. This allows the GPS to provide more
relevant distance information. The VOR approach in the GPS database many
times does not provide published approach distance information, since often
these distances are measured to the MAP, rather than to the VOR.

This is not an approved use of the GPS equipment. VOR approaches are
supposed to be flown using actual VOR course guidance, or as a GPS overlay
approach. The latter must be loaded from the database because there are
operational consequences when you do it that way. Substitution of GPS for
ground-based navaids in the approach phase is limited to DME and ADF.


Additionally, I use the OBS mode to provide situational awareness when
intercepting an airway. If I just departed an airport and am given a
heading and a request to intercept an airway, I switch the GPS to OBS mode,
hit direct-to the VOR (or intersection) defining that leg of the airway,
dial in the airway radial on the VOR OBS, and momentarily flip the GPS/NAV
switch to NAV.

Why just use GPS for situational awareness, when you can use it to navigate?
What you're describing is just the normal GPS technique for radar vectors to
an airway, except that you've added the byzantine step of bring your VOR
back into the equation. You don't need the VOR. If you don't trust the
GPS, you can always back it up with the VOR; turn on the digital readout so
you can see what radial you're on, but leave the NAV/GPS selector set to GPS
and let your GPS navigate for you.


This draws the airway on the moving map (both the KLN94's map and the
multi-function display map), which gives me a good idea where the airway is
relative to my position. Once I intercept the airway, I place the GPS back
in LEG mode and again hit direct-to VOR.

It's not necessary or desirable to hit direct-to VOR in this case. Now this
gets into one of the more esoteric operational characteristics of your GPS,
but whenever you take the GPS out of OBS mode and back to leg mode, if the
TO/FROM flag is presently indicating TO the station (the VOR station is
still in front of you), the GPS will automatically set DTK to the correct
value for your selected OBS course which is ostensibly the airway. In other
words, it automatically does the right thing.

If, on the other hand, you do not roll out precisely on your airway, then
you insist on doing a Direct operation after returning to Leg mode, you have
now decided that it's OK to proceed to the VOR Direct from wherever you
happened to roll out rather than along the charted airway.