GPS/WAAS VNAV approaches and runway length

The Garmin 480 now supports LPV approaches which are ILS like
approaches using WAAS-GPS for both LNAV and VNAV.

My question. I'm assuming the LPV approach would target 1000ft down
the runway as the TDZ (just like an ILS). Does this mean that LPV
approaches will not be added to the airports with smaller runways?

For example, my homefield (3ck)has a 3058 runway. The 1000 ft TDZ
would only leave 2000 ft to get stopped, so I am wondering if an LPV
approach would ever be added at 3ck (or similar airports).

Nathan Young wrote in
:

The Garmin 480 now supports LPV approaches which are ILS like
approaches using WAAS-GPS for both LNAV and VNAV.

My question. I'm assuming the LPV approach would target 1000ft down
the runway as the TDZ (just like an ILS). Does this mean that LPV
approaches will not be added to the airports with smaller runways?

For example, my homefield (3ck)has a 3058 runway. The 1000 ft TDZ
would only leave 2000 ft to get stopped, so I am wondering if an LPV
approach would ever be added at 3ck (or similar airports).

AFAIK the GPS approach uses the end of the runway for the approach point.
The reason an ILS takes you further down is that the GS transmitter is
located down the runway, not at the end. With a GPS, any position can be
used, unlike an ILS where the transmitters have to be placed down the way,
not at the end of the runway because of obstruction and interference reasons.

--
Regards,

Stan

Stan Gosnell wrote:
AFAIK the GPS approach uses the end of the runway for the approach point.
The reason an ILS takes you further down is that the GS transmitter is
located down the runway, not at the end. With a GPS, any position can be
used, unlike an ILS where the transmitters have to be placed down the way,
not at the end of the runway because of obstruction and interference reasons.

I suspect that's not the only reason. Putting the CS 1000 feet down
the runway gives you 50 feet (the height of an FAA-standard tree!)
threshold crossing height. This is convenient to have when your GS
receiving antenna is mounted at a higher elevation than your wheels.
Or is that the "obstruction" reason you mention?

If you follow a synthetic GPS "glide slope" which starts at the
threshold all the way to the ground, your GPS antenna will clear the
approach lights but your wheels won't.

On Fri, 22 Oct 2004 14:08:57 GMT, Nathan Young
wrote:

The Garmin 480 now supports LPV approaches which are ILS like
approaches using WAAS-GPS for both LNAV and VNAV.

My question. I'm assuming the LPV approach would target 1000ft down
the runway as the TDZ (just like an ILS). Does this mean that LPV
approaches will not be added to the airports with smaller runways?

For example, my homefield (3ck)has a 3058 runway. The 1000 ft TDZ
would only leave 2000 ft to get stopped, so I am wondering if an LPV
approach would ever be added at 3ck (or similar airports).

On a few LNAV/VNAV approaches I looked at, the chart was annotated with a
TCH 51'. So assuming you maintain the 3.00° glide path angle, you would
touch down approximately 973' from the runway threshold. That is also
called the Ground Point of Intercept or GPI.

The LPV approach at FDK has a TCH of 50' and a GP angle of 3° -- so it
seems that is about the same.

However, for airports served by smaller aircraft, the procedure specialists
have the option (I believe) of both increasing the GPA and decreasing the
TCH. This would decrease the GPI and allow the use of shorter runways.
How short? I dunno. It seems one could probably get a GPI of 500' or so
but I don't know what that does for minimum runway length for an LPV
approach.


--ron

LPV's are actually built to a TCH. If the airport has an ILS installed,
they'll aim for the same TCH. If they don't have ILS, they'll select a
TCH based on the wheel height group, which is based on the type of
aircraft expected at the runway. Wheel height groups can be found at the
following link, on page 19 of 70. The smaller the aircraft, the lower
the TCH requirement, which would make the touchdown point closer to the
threshold.
http://av-info.faa.gov/terps/Directi...es/8260.50.pdf

The tables in AC 150-5300-13 (pages 48/49 of 57) at
http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/f3e8f0f55c4ebcf986256e290071fd07/$FILE/AC150-5300-13chg6.pdf
give an idea of runway lengths required. 3058' doesn't meet the criteria
for LPV, so to answer your question, no LPV (unless criteria changes).

JPH

Nathan Young wrote:
The Garmin 480 now supports LPV approaches which are ILS like
approaches using WAAS-GPS for both LNAV and VNAV.

My question. I'm assuming the LPV approach would target 1000ft down
the runway as the TDZ (just like an ILS). Does this mean that LPV
approaches will not be added to the airports with smaller runways?

For example, my homefield (3ck)has a 3058 runway. The 1000 ft TDZ
would only leave 2000 ft to get stopped, so I am wondering if an LPV
approach would ever be added at 3ck (or similar airports).

On Fri, 22 Oct 2004 21:13:18 -0500, J Haggerty
wrote:

LPV's are actually built to a TCH. If the airport has an ILS installed,
they'll aim for the same TCH. If they don't have ILS, they'll select a
TCH based on the wheel height group, which is based on the type of
aircraft expected at the runway. Wheel height groups can be found at the
following link, on page 19 of 70. The smaller the aircraft, the lower
the TCH requirement, which would make the touchdown point closer to the
threshold.
http://av-info.faa.gov/terps/Directi...es/8260.50.pdf

The tables in AC 150-5300-13 (pages 48/49 of 57) at
http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/f3e8f0f55c4ebcf986256e290071fd07/$FILE/AC150-5300-13chg6.pdf
give an idea of runway lengths required. 3058' doesn't meet the criteria
for LPV, so to answer your question, no LPV (unless criteria changes).

Great references, thanks. I agree with your assessment - I don't
think 3ck can expect to benefit from one of these approaches anytime
soon. Too bad, as I would have liked the improved minimums... Not
that I would have used them much, but the piece of mind of having an
extra few hundred feet vs an alternate is nice.

-Nathan

Great references, thanks. I agree with your assessment - I don't
think 3ck can expect to benefit from one of these approaches anytime
soon. Too bad, as I would have liked the improved minimums..

I fly a Cessna 172. My ADF is not operating and my avionics shop suggested
removing and installing a Garmin 430.
Now I see that the 480 is available.
What do you guys think? 430 or 480?
Hank

"Hankal" wrote in message =
...
Great references, thanks. I agree with your assessment - I don't
think 3ck can expect to benefit from one of these approaches anytime
soon. Too bad, as I would have liked the improved minimums..
=20
I fly a Cessna 172. My ADF is not operating and my avionics shop =
suggested
removing and installing a Garmin 430.
Now I see that the 480 is available.
What do you guys think? 430 or 480?
Hank

There's a price difference, but the GNS-480/CNX-80 is hugely more =
capable.
---JRC---

There's a price difference, but the GNS-480/CNX-80 is hugely more =
capable.

I think about 2 grand, but waht is my life worth