Is there a noticeable difference between LPV and LNA/VNAV if you fly it with the DFC90, or is it really more a “legal” thing (I know that the precision gets higher the closer you get with the LPV, but already the precision with my normal 430s was so high …)
It’s not precision but scaling. LNAV VNAV has a lateral full-scale deflection of 0.3 nautical miles all the way down. For LPV it increases sensitivity as you approach the runway. If you can fly an LPV without noticing the increasing sensitivity as you approach the runway you’re a better pilot than me!
Bookworm, RTCA DO-229C/D have a different definition of the Full Scale Deflection FSD for LNAV/VNAV approaches than the non WAAS TSO C129 GPS systems which are as you described.
If one is flying an LNAV/VNAV approach with a TSO C146 navigator such as the GNS430W, the FSD lateral CDI is angular, +/- 2 degrees or 0.3 NM whichever is less from the FAF inbound. The error mentioned several time that the Garmin navigator did was to use the angular CDI scaling regardless if it was greater than 0.3 NM. This occurs at just under 7.0 NM, so the reason why the vertical guidance was removed from many approaches had to do with the long final approach segments. Only a handful of approaches in the US were effected. The fix was to make the FSD for the CDI to not exceed 0.3 NM until the angular value was less than 0.3 NM and then switch to the angular FSD value.
Here is a power point presentation that I gave back in 2014. A few things have changed, most notably Garmin has made several updates to their GNS and GTN software and now support the LP approach type and LP with advisory vertical guidance. Much is US specific, but the GNS and GTN work the same.
Here is a presentation I gave to our local controllers regarding issues that pilots experience when joining the approach at a waypoint that is not an IAF.
Hopefully your controllers will do a better job providing direction to pilots to join the approach, but somehow I doubt it. Controllers don’t understand the difference between ground based Navaids and RNAV operations. They also don’t understand that the pilot has to program the GPS to do what the controller wants them to do.
I will have at those tomorrow – thank you very much!
bookworm wrote:
you’re a better pilot than me!
Or have a better flight director….
NCYankee wrote:
Bookworm, RTCA DO-229C/D have a different definition of the Full Scale Deflection FSD for LNAV/VNAV approaches than the non WAAS TSO C129 GPS systems which are as you described.
Thank you NCYankee, I didn’t know that. I’ve spent to much time talking with airline pilots who seem to have different equipment. Now if the CAA here would just get on and code the GPS approach at my local airport to permit vertical guidance, I might actually get some practical experience. ;)
I read through this thread and am still a bit confused. Here is my practical example.
Zurich has an L/VNAV approach for Rwy 14 and the plate gives a DH of 480ft. There is no DH for LPV. If one now has a WAAS capable box and flies this approach can one fly to the equivalent ILS DH or is one stuck at the higher DH inspite of the more accurate gear?
I would opt for the higher DH but just wanted to clarify.
placido wrote:
I read through this thread and am still a bit confused. Here is my practical example.
Zurich has an L/VNAV approach for Rwy 14 and the plate gives a DH of 480ft. There is no DH for LPV. If one now has a WAAS capable box and flies this approach can one fly to the equivalent ILS DH or is one stuck at the higher DH inspite of the more accurate gear?I would opt for the higher DH but just wanted to clarify.
If there is no LPV then you can’t fly one. You must fly an approach available at teh airport and runway and fly to the minima on the approach you are flying. If your box shows LNAV/VANV then you can use that minima.
