LPV vs LNAV/VNAV?

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.

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.

Andrew Sarangan wrote:

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.


The G/S has to be either Baro VNAV or WAAS "electronic" to be certified
for the approach phase of flight, primary or advisory. The VNAV path
provided by a receiver that doesn't have WAAS TSC146 certification would
be very unreliable.

Andrew Sarangan writes:

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.

The cost of certification is probably an important factor.

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

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