A aviation & planes forum. AviationBanter

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below.

Go Back   Home » AviationBanter forum » rec.aviation newsgroups » Instrument Flight Rules
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

LPV vs LNAV/VNAV?



 
 
Thread Tools Display Modes
  #21  
Old January 7th 07, 04:59 PM posted to rec.aviation.ifr
Sam Spade
external usenet poster
 
Posts: 1,326
Default LPV vs LNAV/VNAV?

Stan Prevost wrote:

"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?


Yes.

When VNAV first came in they could only be an an LNAV-only IAP. Then,
quite a few years ago that was changed to permit them for LNAV minimums
on an LNAV/VNAV IAP.
  #22  
Old January 7th 07, 04:59 PM posted to rec.aviation.ifr
Ron Rosenfeld
external usenet poster
 
Posts: 264
Default LPV vs LNAV/VNAV?

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)
  #23  
Old January 7th 07, 05:04 PM posted to rec.aviation.ifr
Jon
external usenet poster
 
Posts: 194
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?


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

  #24  
Old January 7th 07, 05:09 PM posted to rec.aviation.ifr
Mxsmanic
external usenet poster
 
Posts: 9,169
Default LPV vs LNAV/VNAV?

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.
  #25  
Old January 7th 07, 08:20 PM posted to rec.aviation.ifr
Stan Prevost[_1_]
external usenet poster
 
Posts: 71
Default LPV vs LNAV/VNAV?


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


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


Yes.

When VNAV first came in they could only be an an LNAV-only IAP. Then,
quite a few years ago that was changed to permit them for LNAV minimums on
an LNAV/VNAV IAP.


An "advisory" guide slope could only be applied to a final approach segment
without stepdown fixes, or one in which the glide slope clears the
obstacle(s) by the required margin. I doubt that all LNAV-only approaches
have been TERPSed for that, especially those without VDPs.



  #26  
Old January 7th 07, 10:14 PM posted to rec.aviation.ifr
Sam Spade
external usenet poster
 
Posts: 1,326
Default LPV vs LNAV/VNAV?

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

Stan Prevost wrote:


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



Yes.

When VNAV first came in they could only be an an LNAV-only IAP. Then,
quite a few years ago that was changed to permit them for LNAV minimums on
an LNAV/VNAV IAP.



An "advisory" guide slope could only be applied to a final approach segment
without stepdown fixes, or one in which the glide slope clears the
obstacle(s) by the required margin. I doubt that all LNAV-only approaches
have been TERPSed for that, especially those without VDPs.



They aren't TERPsed, rather Jeppesen applies an angle that assures
clearance of the stepdown fixes.

Example:

http://tinyurl.com/y68phr

  #27  
Old January 7th 07, 11:28 PM posted to rec.aviation.ifr
Stan Prevost[_1_]
external usenet poster
 
Posts: 71
Default LPV vs LNAV/VNAV?


"Sam Spade" wrote in message
...


An "advisory" guide slope could only be applied to a final approach
segment without stepdown fixes, or one in which the glide slope clears
the obstacle(s) by the required margin. I doubt that all LNAV-only
approaches have been TERPSed for that, especially those without VDPs.



They aren't TERPsed, rather Jeppesen applies an angle that assures
clearance of the stepdown fixes.

Example:

http://tinyurl.com/y68phr


A very nice example it is, when comparing to the NACO chart
http://tinyurl.com/yfygkv .

NACO computes the descent from the FAWP to the stepdown fix. Jeppesen
computes it from the stepdown fix to the TCH at the runway.

I wonder how the GPS units present the glide slope: 3.67 deg from the FAWP
or 3.61 deg from 0.1 nm after the FAWP. There is only about 30 feet
difference at the stepdown fix between starting the two descent angles at
the FAWP.




  #28  
Old January 7th 07, 11:52 PM posted to rec.aviation.ifr
Sam Spade
external usenet poster
 
Posts: 1,326
Default LPV vs LNAV/VNAV?

Stan Prevost wrote:

"Sam Spade" wrote in message
...


An "advisory" guide slope could only be applied to a final approach
segment without stepdown fixes, or one in which the glide slope clears
the obstacle(s) by the required margin. I doubt that all LNAV-only
approaches have been TERPSed for that, especially those without VDPs.




They aren't TERPsed, rather Jeppesen applies an angle that assures
clearance of the stepdown fixes.

Example:

http://tinyurl.com/y68phr



A very nice example it is, when comparing to the NACO chart
http://tinyurl.com/yfygkv .

NACO computes the descent from the FAWP to the stepdown fix. Jeppesen
computes it from the stepdown fix to the TCH at the runway.

I wonder how the GPS units present the glide slope: 3.67 deg from the FAWP
or 3.61 deg from 0.1 nm after the FAWP. There is only about 30 feet
difference at the stepdown fix between starting the two descent angles at
the FAWP.


NACO is not presenting a VNAV path, rather the descent angle from the
FAF to TDZ elevation.

  #29  
Old January 8th 07, 02:28 AM posted to rec.aviation.ifr
Stan Prevost[_1_]
external usenet poster
 
Posts: 71
Default LPV vs LNAV/VNAV?


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

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

http://tinyurl.com/y68phr



A very nice example it is, when comparing to the NACO chart
http://tinyurl.com/yfygkv .

NACO computes the descent from the FAWP to the stepdown fix. Jeppesen
computes it from the stepdown fix to the TCH at the runway.

I wonder how the GPS units present the glide slope: 3.67 deg from the
FAWP or 3.61 deg from 0.1 nm after the FAWP. There is only about 30 feet
difference at the stepdown fix between starting the two descent angles at
the FAWP.

NACO is not presenting a VNAV path, rather the descent angle from the FAF
to TDZ elevation.


Maybe so, but the angle seems to compute out closer to the descent angle
from FAWP to stepdown, limited by the precision in the numbers on the chart.

The question remains, though, where does the glideslope begin in the GPS
unit: from the FAWP or from the point 0.1 nm after that waypoint?



  #30  
Old January 8th 07, 03:09 AM posted to rec.aviation.ifr
Sam Spade
external usenet poster
 
Posts: 1,326
Default LPV vs LNAV/VNAV?

Stan Prevost wrote:


Maybe so, but the angle seems to compute out closer to the descent angle
from FAWP to stepdown, limited by the precision in the numbers on the chart.

The question remains, though, where does the glideslope begin in the GPS
unit: from the FAWP or from the point 0.1 nm after that waypoint?

\
Beats me. Have you tried to find out in the Garmin Handbook and
couldn't find it?

Having said that, the advisory vertical path is provided to Garmin, and
other avionics vendors, by Jeppesen.

So, assuming no errors on the part of Jeppesen, it doesn't matter
whether you are using their chart or NACO's.

If my butt were on the line I would be keeping an eye on that stepdown fix.

I guess I would have more confidence with L/VNAV.

I would, however, only have complete confidence in LPV.
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
LNAV, VNAV and LPV Andrew Sarangan Instrument Flight Rules 5 January 14th 07 02:57 PM
LNAV preferable over LNAV/VNAV [email protected] Instrument Flight Rules 4 October 16th 05 06:34 PM
GPS approaches with VNAV vertical guidance Doug Instrument Flight Rules 18 November 2nd 04 11:36 PM
CNS-80 VNAV John R. Copeland Instrument Flight Rules 17 October 28th 04 04:24 AM
Which GPS Support LNAV/VNAV? C Kingsbury Instrument Flight Rules 1 October 23rd 04 12:28 AM


All times are GMT +1. The time now is 12:24 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 AviationBanter.
The comments are property of their posters.