LPV vs LNAV/VNAV?

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.

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.

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.



I am sure you are correct, but it doesn't seem to make a whole lot of
sense too keep a useful feature out of certification unless there is
something dangerous about it. I don't see anything unsafe about
providing a glideslope to a nonprecision approach.

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.

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?

But handhelds aren't certified, so there's no guarantee of correctness.


The basic requirement they don't meet is the Integrity requirement,
e.g. the guarantee a) that the error can be bounded and b) that
sufficient warning can be provided when Integrity can not be met.

129 boxes aren't certified for Vertical Guidance, so I suspect that,
even for an NPA (LNAV) approach the same would hold true.

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.

The lack of certification is based on Standalone (Unaugmented) GPS not
being certified for Vertical guidance. This traces to the fact that the
dominant error (after SA was turned off) is the Ionospheric component
and the recevier's model (Klobuchar) is not certified to provide
sufficient Integrity for the Vertical component. With SBAS (e.g. WAAS
in the US), the Integrity requirement has been proven to be met with
sufficient Availability over the Service Volume, to approve approaches
with Vertical Guidance,.

Note that when even when the 145/6 boxes were deployed up in Alaska
(Capstone project), WAAS had yet to be commissioned, and thus the
published approaches were LNAV only.

Also note, there had been talk of building newer 129 boxes, but with
the 145/6 boxes now out, the manufs. apparently can't cost justify
upgrading a box that still wouldn't perform as well as the 145/6

--
Peter

Regards,
Jon

Andrew Sarangan wrote:

displayed as a glideslope

Just took a "flight" using the GNS400W simulator (the GNS430 with WAAS)
becasue I wanted to see if the new WAAS upgrade for the 430/530 would do
this. I flew both a VOR approach and an RNAV/GPS approach that only had
LNAV minimums.

For the VOR approach the GPS did not provide a glideslope, but for the
RNAV/GPS approach into Weedsport, NY (B16 - RNAV/GPS 28):

http://www.myairplane.com/databases/...s/09225R28.PDF

the GPS went into LNAV+V mode and a glideslope indicators on the HSI went
live, as you can see he

http://img119.imageshack.us/img119/6...7010417ev0.jpg



--
Peter

Andrew Sarangan wrote:

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.


LNAV+V

On 6 Jan 2007 21:33:52 -0800, "Andrew Sarangan"
wrote:


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.

The CNX80/GNS480 with current SW will do that for many (not all) LNAV
approaches. It is called advisory vertical guidance and available when
published. I believe the presence of a VDP is one factor that usually
triggers this availability.
Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

Andrew Sarangan wrote:
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.



Perhaps because that functionality is not at all desirable. The "dive
and drive" term is derisive, however, it is important to get to minimums
in order to be able to see the airport. Arriving right at the minimum
altitude just as you reach the place/time for going missed does not do
you any favors.

On Tue, 13 Mar 2007 10:33:43 -0400, Tim 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.

Many LNAV approaches have what is termed "advisory vertical guidance". ON
those approaches, a TSO146c box will output a GP signal that can be used
for a stabilized approach (versus the dive and drive approach). MDA does
not change. On the approaches with which I am familiar, the interception
of the advisory vertical guidance with the MDA may be prior to a VDP,
although they are designed to cross at that point. The guidance goes down
to the MAP or runway end.
Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

Andrew Sarangan 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.


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.


With the 146 spec you will often have an advisory glideslope to MDA.
That is the LNAV+V mode and will be provided if Jeppesen has coded that
capability into the approach's database string. As Garmin says in the W
handbood, not all LNAV-only IAPs have been so coded.

Sam Spade wrote:

Andrew Sarangan 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.



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.


With the 146 spec you will often have an advisory glideslope to MDA.
That is the LNAV+V mode and will be provided if Jeppesen has coded that
capability into the approach's database string. As Garmin says in the W
handbood, not all LNAV-only IAPs have been so coded.

I misstated that somewhat.

If I read it correctly (assuming WAAS is available and passes muster)
you will always get LNAV+V on an LNAV-only IAP, thus you will have
vertical guidance to MDA.

If, on the other hand, it is an LNAV/VNAV approach you will get L/VNAV
if Jeppesen has that approach so coded, otherwise you will get LNAV+V.
You'll have vertical guidance in both cases, but I presume you can only
use the DA concept and VNAV minimums if you get the L/VNAV annuciation.