LPV vs LNAV/VNAV?

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

\
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.


That's why I didn't even look in Garmin material. :-)

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


Whether it matters depends on how much you care about 30 feet. If the GPS
box has you begin the Jepp descent angle at the FAWP, then you wind up 30
feet low at the stepdown fix, if I did the numbers right.


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

For sure!

test

"paul kgyy" wrote in message
ups.com...
Can someone explain to me the difference between these two approach
types, and how they relate to WAAS?

A sample approach that has both is KARR RNAV(GPS) RWY 9. LPV DA is
956, LNAV/VNAV DA is 990.

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)

"Ron Rosenfeld" wrote in message
...
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.

Ron, do you have any idea why the actual intercept is not at the designed
point?

Stan

On Tue, 13 Mar 2007 19:31:58 -0500, "Stan Prevost"
wrote:


"Ron Rosenfeld" wrote in message
.. .
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.

Ron, do you have any idea why the actual intercept is not at the designed
point?

Stan


Stan,

I miswrote. Actually, at KEPM, the vertical path does intercept the MDA at
the VDP for both GPS approaches. What I was thinking about when I wrote,
was that the VDP is further from the MAP than the minimum visibility for
the approach. (VDP is 1.3 NM from AER; visibility minimums is 1.0 NM)

For an interesting GPS GP, look at the Jepp chart, if you have it, for the
RNAV (GPS) RWY 28 at KPQI. The GP starts down about 0.3 NM after the FAF.
This appears to be done in order to meet a crossing altitude restriction
insice the FAF, and still have a profile that brings you to an appropriate
height closer in to the runway.
Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

"Ron Rosenfeld" wrote in message
...
On Tue, 13 Mar 2007 19:31:58 -0500, "Stan Prevost"
wrote:


For an interesting GPS GP, look at the Jepp chart, if you have it, for the
RNAV (GPS) RWY 28 at KPQI. The GP starts down about 0.3 NM after the FAF.
This appears to be done in order to meet a crossing altitude restriction
insice the FAF, and still have a profile that brings you to an appropriate
height closer in to the runway.


I only have the NACO chart, and it doesn't show up that way. Shouldn't they
be the same if it is necessary to meet obstacle criteria?

On Tue, 13 Mar 2007 21:53:19 -0500, "Stan Prevost"
wrote:


"Ron Rosenfeld" wrote in message
.. .
On Tue, 13 Mar 2007 19:31:58 -0500, "Stan Prevost"
wrote:


For an interesting GPS GP, look at the Jepp chart, if you have it, for the
RNAV (GPS) RWY 28 at KPQI. The GP starts down about 0.3 NM after the FAF.
This appears to be done in order to meet a crossing altitude restriction
insice the FAF, and still have a profile that brings you to an appropriate
height closer in to the runway.


I only have the NACO chart, and it doesn't show up that way. Shouldn't they
be the same if it is necessary to meet obstacle criteria?





I didn't think the NACO charts showed the GPS GP profile. Let me check at
KPQI ... Interesting difference.

On the Jepp chart it also shows a 3.25° GP, which intersects PESIC at
1200'.

The GP runs level from LISDE for 0.3 NM, with top of descent 4.4 NM from
HUMAX and ends at HUMAX but below the MDA.

The NACO chart also shows a 3.25° GP intersecting at PESIC at 1200', but it
appears to run smoothly from LISDE (which is 4.7 NM from HUMAX. Obviously
both cannot be correct.

Doing some trigonometry it appears the JEPP chart is correct:

PESIC--LISDE = 3.2 NM

PESIC--Top of Descent of GP = 2.9 NM (4.4-1.5)

The "triangle:


Height = 1000' (LISDE 2200- PESIC 1200)
Angle = 3.25°

Base = 1000 / tan (3.25°)

= 2.9 NM


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

On Tue, 13 Mar 2007 21:53:19 -0500, "Stan Prevost"
wrote:


"Ron Rosenfeld" wrote in message
.. .
On Tue, 13 Mar 2007 19:31:58 -0500, "Stan Prevost"
wrote:


For an interesting GPS GP, look at the Jepp chart, if you have it, for the
RNAV (GPS) RWY 28 at KPQI. The GP starts down about 0.3 NM after the FAF.
This appears to be done in order to meet a crossing altitude restriction
insice the FAF, and still have a profile that brings you to an appropriate
height closer in to the runway.


I only have the NACO chart, and it doesn't show up that way. Shouldn't they
be the same if it is necessary to meet obstacle criteria?





Looking at it another way, also using trig and the same values, if you were
to start down at LISDE at 3.25°, by the time you got to PESIC (3.2 NM) you
would have descended 1104' instead of only 1000', so you would be 104' low
at PESIC.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

On Tue, 13 Mar 2007 21:53:19 -0500, "Stan Prevost"
wrote:


"Ron Rosenfeld" wrote in message
.. .
On Tue, 13 Mar 2007 19:31:58 -0500, "Stan Prevost"
wrote:


For an interesting GPS GP, look at the Jepp chart, if you have it, for the
RNAV (GPS) RWY 28 at KPQI. The GP starts down about 0.3 NM after the FAF.
This appears to be done in order to meet a crossing altitude restriction
insice the FAF, and still have a profile that brings you to an appropriate
height closer in to the runway.


I only have the NACO chart, and it doesn't show up that way. Shouldn't they
be the same if it is necessary to meet obstacle criteria?





I don't use NACO charts, but could it be that on the NACO chart, the 3.25°
notation only applies to the segment after PESIC?


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)