Replacing GNS530/430W to take advantage of VNAV in my Jetprop

eal wrote:

Presumably the LNAV+V would allow the autopilot to couple with the vertical glide slope, although l would manually have to disconnect at MDA?

Yes GTN LNAV+V can be flown coupled with AP hooked to glideslope (as well as GTN visual approach can be flown coupled)

Just few caveats on LNAV+V, but you probably know
- M/DA is still on LNAV minima (not LNAV/VNAV minima) plus small epsilon from CDFA addon
- Advisory GP: one has to cross-check altitude & distance vs plate (just as you do on LNAV, or even ILS)
- Aircraft won’t hit anything on LNAV+V if other people can fly Baro-VANV as long as vertical accuracy is good*

In G1000, it does happen to see quick blips of -1000fpm while AP is tracking VPATH near -500fpm (sort of GPS VNAV for cruise descent), not sure if this is related to vertical air mouvements, low vertical GPS VPL accuracy, or low accuracy in ENR mode, lack of SBAS but I would watch my RoD and distance/altitude carefully near the ground with autopilot coupled to LNAV+V even before hitting M/DA ;)

eal wrote:

l guess my question is relevant to the UK with the loss of LPV

Indeed, funnily enough we will keep LNAV/VNAV which uses ENGOS inside GTNs but not LPV which also uses ENGOS inside GTN ;)

From the current IFD540 Pilot Guide:

On* – Will transmit a glideslope deviation signal for display on external indicators (e.g. HSI, EFIS) for approaches that don’t have a published glideslope associated with them. Advisory glideslope will be displayed for RNAV approaches, GPS approaches, and approaches that are authorized for a GPS overlay regardless of SBAS. In a nonSBAS environment, if one of those kinds of approaches is selected and it has a published flight path angle in the database, then expect LNAV+V;

Could this be the key:

and it has a published flight path angle in the database

but one would think that would affect Garmin equally, and I recall there was a bug in that area, years ago…

UK LPV thread and yes, losing official LPV won’t affect UK pilots much because they will still have +V, which is awfully close, albeit with a higher minima, although most UK LPV IAPs (actually most UK IAPs) have silly-high minima.

eal wrote:

I will certainly treat +V as non precision and monitor it like a hawk, should l ever get it working. Any automation aid for Single pilot IFR in marginal weather is a worthy upgrade goal which l would consider coupled +V to be.

I would think that approaches with LNAV/VNAV in the database would still be usable in the UK and would be an APV procedure using EGNOS as SBAS to provide vertical guidance to a DA. In addition, most straight-in approaches with an LNAV minima will be LNAV+V annunciation.

Peter wrote:

and it has a published flight path angle in the database

I would expect this to be the default case. At one point in time, some LNAV or LP procedures in the US were coded with a zero in the DB for the VDA, but this is now long gone history. Now in the US, a VDA is determined and if the visual segment is not clear on a 20 to 1 slope, the US charts don’t include a VDA or TCH, but the Jeppesen charts do. Regardless of what is charted, if the approach designer includes the VDA and TCH, the Garmin GPS will provide +V. If you follow the +V below the MDA, there are no assurances you will not hit an obstacle.