Today's Message Index:
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1. 01:37 PM - Fw: Advisory Glideslope on LP approaches ISSUE=138781 PROJ=1 (Bill Judge)
2. 06:53 PM - Re: Fw: Advisory Glideslope on LP approaches ISSUE=138781 PROJ=1 (Marty Helller)
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Subject: | Fwd: Advisory Glideslope on LP approaches ISSUE=138781 PROJ=1 |
So I noticed a while back that "advisory glide slope" disappeared from GPS
17 at KSEE, my home field.
I thought something broke... but after flying recently with an instructor
during an IPC I found out that the new LP approaches(that sometimes have
lower minima) do not support advisory glideslope, at least the Garmin 430
LP implementation doesn't support advisory glideslope.
Background: For the guys that upgraded to WAAS, it was a pleasant surprise
that all the non precision approaches suddenly had glideslope added, this
allowed you to easily set up a stabilized approach much like an ILS on any
GPS approach as long as you kept in mind that the baro altimeter and
horizontal position was the actual guidance for where you belong
vertically. You could still "chop and drop" but the 430 would connect the
dots and give you "advisory vertical guidance" allowing for the hallowed
stabilized approach.
LP came along and the FAA decided that this advisory glideslope business
just has to go away. So in 2009 when Garmin implemented the LP approaches
in the 430 they deleted the glideslope.
Then in 2011 the FAA recognized their mistake and published AC 90-107 and
now allows advisory glideslope.
So I thought I'd see what Garmin's position was on this. The answer is
below. I think basically they are saying 430 owners shouldn't hold their
breath.
I suspect that more and more LP approaches will be coming online...
Bummer.
Bill
N84WJ, RV-8 915 hrs
rv-8.blogspot.com
*Brief description of the problem:*
Good Afternoon Sir,
While we understand the FAA's position on using advisory guidance the
option to use it while flying a LP approach is limited by software. The
advisory circular you quote was published on 2/11/11, while the GNS
software that was first compatible with LP approaches dates back to 2009.
It wasn't until the last 6 months or so that LP approaches had enough
presence to disrupt LNAV+V approaches replacing the +V with lower minimums.
At this point the +V advisory guidance cannot be made available to you
until/unless new software is made available for the GPS device that is
being used. Garmin is aware of the impact that these changes have made on
flying these approaches and will accommodate you as soon as possible.
Please be aware that the process required to release new software is a long
one and this feature may be some time down the road. I am not in a position
to confirm if and or when this feature may be returned to your
product. Please stay tuned for potential future S.W. updates for your GNC
430W.
Best Regards,
Message 2
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Subject: | Fwd: Advisory Glideslope on LP approaches ISSUE=138781 PROJ=1 |
Hey Bill=2C its been a few years since working in support of the FAA's WAAS
program office so my info might be dated.... That said=2C there is a reaso
n why some RNAV / Gps approaches didn't quaily for LPV minima. Usual its c
lose in obstacles...basically the same as an ILS=2C and why people are disa
ppointed that it didn't solve their localizor only approach limitation. Se
cond could be course alignment =2C enough for staight in but still a close
in turn=2C and or other reasons. The FAA first priority was to build LPVs
whereever possible.
LP was the alternative=2C with usually better minima than a LNAV (height-wi
se) because the obstacle protection zone is smaller. But LPs also took a lo
t of extra programing for Garmin who didn't see the business case while the
re weren't many LPs out there=2C and thousands of LNAV's out there. There
is also a programming issue because the approach is really now a data file
=2C and so either it has vertical (LPV) or not (LP). Its a data block in t
he file that's either on or off. In other words an LP + VNAv would be an L
PV and the FAA would have given you an LPV if there wasn't a reason they co
uldn't.
Ref minima...
Visibility minima is partly based on the distance needed to see the runway
from the MAP. By design=2C the LNAV MAP is the runway end=2C while the LPV
=2C and LnAV/VNAV decision height is usually at the beginning of the approa
ch lights=2C based on approach angle/height and other Terps magic.
So while the LNAV visability is nearly always lower=2C the aircraft usually
is not in a position to land if its at MAP when seeing the runway. (Simi
lar to other non -precision approaches.) Unlike a Vertically guided approa
ch which will have an airplane (on course/glideslope) in position to land
if seeing the runway at decision height=2C further=2C but not as high from
the runway.
If not confused yet=2C I can keep typing....
Marty Heller=2C RV-7 120 hours=2C KSUT
From: bjudge@gmail.com
Subject: RV-List: Fwd: Advisory Glideslope on LP approaches ISSUE=138781
PROJ=1
So I noticed a while back that "advisory glide slope" disappeared from GPS
17 at KSEE=2C my home field.
I thought something broke... but after flying recently with an instructor d
uring an IPC I found out that the new LP approaches(that sometimes have low
er minima) do not support advisory glideslope=2C at least the Garmin 430 LP
implementation doesn't support advisory glideslope.
Background: For the guys that upgraded to WAAS=2C it was a pleasant surpris
e that all the non precision approaches suddenly had glideslope added=2C th
is allowed you to easily set up a stabilized approach much like an ILS on a
ny GPS approach as long as you kept in mind that the baro altimeter and hor
izontal position was the actual guidance for where you belong vertically. Y
ou could still "chop and drop" but the 430 would connect the dots and give
you "advisory vertical guidance" allowing for the hallowed stabilized appro
ach.
LP came along and the FAA decided that this advisory glideslope business ju
st has to go away. So in 2009 when Garmin implemented the LP approaches in
the 430 they deleted the glideslope.
Then in 2011 the FAA recognized their mistake and published AC 90-107 and n
ow allows advisory glideslope.
So I thought I'd see what Garmin's position was on this. The answer is belo
w. I think basically they are saying 430 owners shouldn't hold their breath
.
I suspect that more and more LP approaches will be coming online...
Bummer.
BillN84WJ=2C RV-8 915 hrsrv-8.blogspot.com
Brief description of the problem:
Good Afternoon Sir=2C
While we understand the FAA's position on using advisory guidance the optio
n to use it while flying a LP approach is limited by software. The advisory
circular you quote was published on 2/11/11=2C while the GNS software that
was first compatible with LP approaches
dates back to 2009. It wasn't until the last 6 months or so that LP approa
ches had enough presence to disrupt LNAV+V approaches replacing the +V with
lower minimums.
At this point the +V advisory guidance cannot be made available to you unti
l/unless new software is made available for the GPS device that is being us
ed. Garmin is aware of the impact that these changes have made on flying th
ese approaches and will accommodate
you as soon as possible. Please be aware that the process required to rele
ase new software is a long one and this feature may be some time down the r
oad. I am not in a position to confirm if and or when this feature may be r
eturned to your product. Please
stay tuned for potential future S.W. updates for your GNC 430W.
Best Regards=2C
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