A colleague did a flight with a GTN650 driving a G5.
To play with the system, he selected an NDB approach. A glideslope appeared, which he followed, but after a bit it disappeared.
I have no more info except that it disappeared well before the NDB IAP DH.
Thinking about this, this may well be how +V is supposed to work. How else could the user interface be implemented? Either the GPS displays an explicit “+V” option next to each “official” IAP, OR it allows you to select the “official” IAP and then displays the lateral guidance and the “+V” glideslope. The glideslope will then logically vanish at the official IAP DH.
This also relates to this Q.
+V (advisory vertical) is annunciated only on GPS approaches using the GTN. The basic annunciation is either LNAV or LP and if the approach has +V, then the annunciation is LNAV+V or LP+V as appropriate. Other annunciations are LPV or L/VNAV. The vertical CDI appears the same regardless of the annunciation if vertical guidance or advisory vertical guidance is provided. The vertical guidance becomes active when the PFAF or FAF is the active fix on the approach procedure and remains on as long as it is not flagged until the GP hits the pavement. Since +V does not appear on conventional procedures, I am guessing what you were seeing is VNV (Vertical Navigation) where descents from a TOD to a BOD are provided a different form of vertical guidance. The VNV is based on Baro VNAV and the GTN provides altitudes for each leg of the descent. The VNV GP indicator on my G500TXi is a different symbol than the GPS based Vertical guidance.
See the screenshots of an LPV approach where both VNV and Vertical Guidance are used. The descent using VNV is to 2100 feet and uses Baro VNAV for the vertical track. This changes to the LPV GP at the FAF and is based on GPS altitude. So you probably saw VNV to the FAF on your colleague’s flight as there isn’t any +V past the FAF on a conventional approach procedure.
NCYankee wrote:
+V (advisory vertical) is annunciated only on GPS approaches using the GTN.
This is of course true, but it is annunciated also on GPS overlays of non-RNP approaches.
There was a US program of GPS overlays on conventional approach procedures. They were named “or GPS” in the title to indicate that either a GPS or the conventionla navigation aide could be used for the procedure. Was this ever done outside the USA? Most of the “or GPS” overlay approaches are now gone in the USA, although there still are a few.
I am not sure whether they are called “overlays” but IFR GPSs tend to contain representations of non-GPS procedures. These can be extremely basic; for example in the KLN94 they can be pretty useless. I have not seen one thus named published by Jeppesen.
