LPV vs LNAV/VNAV?

paul kgyy wrote:

Both of these options require a WAAS receiver, I presume?

Yes, and if WAAS is not available to the standards required by the specs
then the 146 box will not accept the WAAS solution, which means (using
Garmin as an example) LPV, L/VNAV, and LNAV+V will not be available;
only LNAV will be available.

"Sam Spade" wrote in message ...
paul kgyy wrote:

Both of these options require a WAAS receiver, I presume?

Yes, and if WAAS is not available to the standards required by the specs
then the 146 box will not accept the WAAS solution, which means (using
Garmin as an example) LPV, L/VNAV, and LNAV+V will not be available;
only LNAV will be available.

And I can attest to that, Sam, because I've experienced having an
LNAV/VNAV approach "Downgraded to LNAV" only.
I couldn't take the time just then to check the SV reception page,
to see if the problem might have been explained there.

Sam Spade wrote:

paul kgyy wrote:

Both of these options require a WAAS receiver, I presume?

Yes, and if WAAS is not available to the standards required by the specs
then the 146 box will not accept the WAAS solution, which means (using
Garmin as an example) LPV, L/VNAV, and LNAV+V will not be available;
only LNAV will be available.

I don't think so. A TSO C129a GPS driving a FMS with baro VNAV should be able to fly RNAV(GPS)
approaches using LNAV/VNAV minimums. No WAAS involved.

Mike

Mike Adams wrote:

Sam Spade wrote:


paul kgyy wrote:


Both of these options require a WAAS receiver, I presume?


Yes, and if WAAS is not available to the standards required by the specs
then the 146 box will not accept the WAAS solution, which means (using
Garmin as an example) LPV, L/VNAV, and LNAV+V will not be available;
only LNAV will be available.


I don't think so. A TSO C129a GPS driving a FMS with baro VNAV should be able to fly RNAV(GPS)
approaches using LNAV/VNAV minimums. No WAAS involved.

Mike

That has been true for a long time. The context of the recent
discussions in this forum have been about TSO C-146 (RTCA DO-229C).

Sam Spade wrote:
paul kgyy wrote:

Both of these options require a WAAS receiver, I presume?

Yes, and if WAAS is not available to the standards required by the specs
then the 146 box will not accept the WAAS solution, which means (using
Garmin as an example) LPV, L/VNAV, and LNAV+V will not be available;
only LNAV will be available.

Something I never understood is why LNAV approaches don't automatically
show a glideslope so that the airplane arrives at the MDA at the VDP.

Andrew Sarangan writes:

Something I never understood is why LNAV approaches don't automatically
show a glideslope so that the airplane arrives at the MDA at the VDP.

Because L stands for lateral?

--
Transpose mxsmanic and gmail to reach me by e-mail.

Andrew Sarangan wrote:

Something I never understood is why LNAV approaches don't automatically
show a glideslope so that the airplane arrives at the MDA at the VDP.

Perhaps because it wasn't part of the certification at the time?

--
Peter

Peter R. wrote:
Andrew Sarangan wrote:

Something I never understood is why LNAV approaches don't automatically
show a glideslope so that the airplane arrives at the MDA at the VDP.

Perhaps because it wasn't part of the certification at the time?


Perhaps my comment was not clearly stated. When you fly an LNAV
approach (or any nonprecision approach for that matter) instead of the
traditional dive and drive you can mentally calculate the vertical
speed required (VSR) to arrive at the VDP at a constant glide angle .
That mental calculation could be easily performed by the GPS and
displayed as a glideslope. But I have not seen any GPS do that.
Certification is irrelevant. We are not talking about a lower minimum
or anything new that we not already allowed to do.

Andrew Sarangan wrote:

That mental calculation could be easily performed by the GPS and
displayed as a glideslope. But I have not seen any GPS do that.
Certification is irrelevant.

Certification is most certainly relevant to your query, as that is most
likely what kept that feature out of the TSO C129a certified IFR GPS's.

A handheld Garmin 196 (I think that is the model a pilot-friend had with
him a couple of years ago) that we took up on a practice IFR flight did
just that. It displayed a glideslope for a non-precision approach. If the
cheaper handhelds can do it, then why don't their IFR-certified TSO C129a
big brothers do it? Because it wasn't part of the certification and
therefore, regardless of their ability to provide this feature, are
restricted from doing so due to the certification.

--
Peter

Peter R. wrote:

Andrew Sarangan wrote:


That mental calculation could be easily performed by the GPS and
displayed as a glideslope. But I have not seen any GPS do that.
Certification is irrelevant.


Certification is most certainly relevant to your query, as that is most
likely what kept that feature out of the TSO C129a certified IFR GPS's.

True, and that capability is permitted by the 146 spec. It does require
WAAS.

This is from the Garmin 500W handbook:

LNAV/VNAV and LNAV Approaches with Advisory
Vertical Guidance

GPS approaches with vertical guidance may be either LNAV/VNAV or LNAV
approaches with advisory vertical guidance. LNAV-only approaches with
advisory
vertical guidance only have LNAV minima listed on the bottom of the
approach plate. The glidepath is typically denoted by a light dashed
line on the vertical profile (Jeppesen only) with an associated
glidepath angle (usually in the 3.00° range). These approaches are
indicated with “LNAV+V”.

For approaches with LNAV/VNAV minimums, those will be controlling. For
LNAV approaches with advisory vertical guidance, the LNAV minimums will
be controlling. Approaches confirmed as “LNAV/VNAV” approaches in the
Jeppesen NavData are indicated

with an “L/VNAV” annunciation. At the time of this publication, not all
of the LNAV/VNAV approaches have been identified as such in the Jeppesen
NavData, therefore some LNAV/VNAV approaches may still be identified
with “LNAV+V” annunciation.