Huh? My Sys 60 PSS enters GS capture mode when I press GS (ALT illuminated, GS blinking). It only starts to track the GS once the needle crosses the center line, at which point ALT goes dark and GS stops blinking.
Press again GS and it will engage and try to get to it. That’s the “manually engage” feature.
That said, not having a “W” box I have no idea how one configures one of those to capture the advisory glideslope…
There is no difference between a glideslope from an ILS and an advisory glideslope from an LNAV+V.
Peter,
Your description isn’t quite right.
You have LNAV, LNAV/VNAV and LPV. They are all certified, and each has its own minima.
LNAV may additionally have a synthesised, uncertified, advisory glideslope, and be captioned LNAV+V. That is in the gift of Garmin, not the AIP/Jeppesen process and is only to help you fly the CDFA. Its minima are the same as LNAV.
LNAV+V could quite happily fly you into an obstacle or terrain, which is exactly what it does in Sidney NY. It is to be treated with caution and always backed up by CDFA and step down fixes.
which is exactly what it does in Sidney NY.
Presumably only if you go below the MDA, which is fair enough… The Sidney is a well discussed case but it is a non-precision IAP so…
Obstacle clearance below the MDA is not assured if the L+V trajectory is continued, except on ILS or GPS/LPV.
Isn’t LNAV/VNAV only for BARO-VNAV aircraft i.e. not light GA? I am not sure.
Isn’t LNAV/VNAV only for BARO-VNAV aircraft i.e. not light GA?
No, not at all. It was originally used for aircraft with FMS systems and used BARO-VNAV. Now can be flown with WAAS GPS.
So a WAAS GPS can fly an approach published for BARO-VNAV, with vertical guidance?
Which vertical profile is it tracking?
The +V advisory glideslope, or the LPV glideslope?
Which light GA avionics support BARO-VNAV?
Not quite: LNAV/VNAV approaches can be flown either by baro-vnav or by waas gps. This tracks the VNAV glideslope as surveyed and intended by the procedure designer. Some VNAV approaches are not permitted for GPS operations – in this case you will only get LNAV guidance: you won’t get a +V glideslope.
For (hypothetical) approaches with all three of LNAV, LNAV/VNAV, and LPV minima the system will choose the best available. The LPV glideslope may well be coincident with the VNAV glideslope, but the presentation would be different as the LPV glideslope has a much smaller distance to full scale deflection (it’s more like an ILS).
LNAV+V is a garmin provided pseudo glideslope linking the FAF to the MAP. If the gps degrades from VNAV or LPV to LNAV only then the +V glideslope will be inhibited.
Do the non-garmin boxes give +v glideslopes on LNAV only approaches? IMO this is a killer feature.
Do the non-garmin boxes give +v glideslopes on LNAV only approaches? IMO this is a killer feature.
Actually interesting to know if the new Avidyne boxes do an advisory glideslope.
Which light GA avionics support BARO-VNAV?
None – not even the G1000 can do this on an approach.
The same glideslope can however be flown by a waas gps, if the approach is approved for this.
The UK and Sweden (at least) seem to be lagging behind approving VNAV approaches for GPS. Germany certainly supports them; I flew one at EDDG on Saturday.
The G1000 supports Baro VNAV, but not for the intermediate and final approach segments. The only exception to this is the Garmin King Air retrofit STC which does support Baro VNAV for approaches. The WAAS GPS units are also certified in the US to fly the LNAV/VNAV minimum line on an RNAV approach using the WAAS for vertical guidance in lieu of a Baro VNAV system. There are some approaches outside of the WAAS service area, for example in Puerto Rico, that WAAS is not permitted to fly the vertical for the LNAV/VNAV and this is noted on the approach charts. Flying the LNAV/VNAV with Baro VNAV does not require WAAS for the lateral guidance and uses the Baro VNAV for the vertical, but has temperature limitations. If the approach is within the WAAS service limits, a WAAS GPS may fly the LNAV/VNAV without any temperature limitation since the vertical guidance is not affected by temperature. The vertical path flown by the WAAS is not identical to the one flown by a Baro VNAV, but the vertical full scale deviations are limited on the WAAS path so that the two paths are close enough. The Baro VNAV path is a curved path in space whereas the WAAS VNAV path is a straight line in space.
Many thanks for the detailed explanation, jwoolard and NCYankee 
I have to admit, this is damn complicated…
… +v glideslopes on LNAV only approaches? IMO this is a killer feature.
I agree 100% – LPV is very slow coming to Europe in an operationally significant way (airports with Customs but no ILS, etc). I have written to Avidyne asking the question.
