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LPV vs LNAV/VNAV?



 
 
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  #11  
Old January 7th 07, 06:57 AM posted to rec.aviation.ifr
Peter R.
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Posts: 1,045
Default LPV vs LNAV/VNAV?

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
  #12  
Old January 7th 07, 07:09 AM posted to rec.aviation.ifr
Peter R.
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Posts: 1,045
Default LPV vs LNAV/VNAV?

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
  #13  
Old January 7th 07, 03:14 PM posted to rec.aviation.ifr
Sam Spade
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Posts: 1,326
Default LPV vs LNAV/VNAV?

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).
  #14  
Old January 7th 07, 03:17 PM posted to rec.aviation.ifr
Sam Spade
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Posts: 1,326
Default LPV vs LNAV/VNAV?

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.
  #15  
Old January 7th 07, 03:18 PM posted to rec.aviation.ifr
Sam Spade
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Default LPV vs LNAV/VNAV?

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
  #16  
Old January 7th 07, 03:22 PM posted to rec.aviation.ifr
Sam Spade
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Posts: 1,326
Default 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.
  #17  
Old January 7th 07, 03:27 PM posted to rec.aviation.ifr
Sam Spade
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Posts: 1,326
Default LPV vs LNAV/VNAV?

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.
  #18  
Old January 7th 07, 04:17 PM posted to rec.aviation.ifr
Stan Prevost[_1_]
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Posts: 71
Default LPV vs LNAV/VNAV?


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


Can an RNAV approach have stepdown fixes on the final approach segment?


  #19  
Old January 7th 07, 04:37 PM posted to rec.aviation.ifr
Andrew Sarangan
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Posts: 382
Default 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.

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.

  #20  
Old January 7th 07, 04:57 PM posted to rec.aviation.ifr
Sam Spade
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Posts: 1,326
Default LPV vs LNAV/VNAV?

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.
 




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