How much protection on approach?

(Michael) wrote:
I fail to see how this is relevant to the protection offered on
approach. The hazard on the approach into LVJ is a 1200 ft tower.
That tower is actually much CLOSER to the FAC on the GPS approach.

Why not call up the local tracon, ask to speak to the procedures guru,
and find out from somebody who is in a position to know for sure?

Roy Smith wrote
I fail to see how this is relevant to the protection offered on
approach. The hazard on the approach into LVJ is a 1200 ft tower.
That tower is actually much CLOSER to the FAC on the GPS approach.

Why not call up the local tracon, ask to speak to the procedures guru,
and find out from somebody who is in a position to know for sure?

To know what for sure?

Michael

(Michael) wrote in message m...

Approaches where the navaid is off the field are of necessity
constrained by the location of the navaid.

Actually, whether the navaid is on or off the field, there are still
plenty of constraints on the approach unless it's in the middle of
nowhere on flat ground.

Granted. Let's do the math:

GPS approach: constrained by airspace, terrain, and obstructions

off field navaid approach: constrained by airspace, terrain, obstructions
*and* the location of the navaid.

It appears pretty clear to me that the latter is more constrained.
YMMV

Stand-alone GPS
approaches IMO add significant capability vs. using VFR GPS
to fly an impromptu overlay approach.

I fail to see how this is relevant to the protection offered on
approach.

Yes, I know. We've had this discussion before. It seems
obvious to me that it's relevant. In the case you cite,
apparently the GPS approach doesn't avoid the tower. However,
with a GPS, the capability to establish a waypoint at a
convenient spot clearly allows the approach designer to work
around terrain and obstructions in a way that an approach
based on one or two ground navaids can not.

It's simply that the GPS (VFR or IFR) is so much more accurate than
the VOR, and thus the pilot can easily avoid the hazard without the
need to keep the needle perfectly centered.

This is definately a factor, but it's not the factor to which
I was referring.

If a VFR GPS is used to
back up the VOR approach, then I would argue that safety is increased
over the standalone GPS approach, since (a) the hazard is
significantly farther from the FAC and (b) a second source of
navigation, relying on a completely different signal source, is
available as a sanity check.

You may even be correct in this instance, but I don't think that
can be generalized, nor can it be generalized that the capabilies/
safety of IFR and VFR GPS are equal.

I understand some VFR GPS can be set to precise course guidance
(full deflection = 0.3 miles) and of course a VFR GPS can be
installed so as to have the same features of IFR GPS -- RAIM
prediction and monitoring, installed antenna etc. But many
are not installed or set up that way.

You don't have to agree with my point, but please don't delete
it and then surmise that I must have been making a different
one.

It simply never occurred to me that your point was that having the IFR
rather than a VFR GPS was a safety issue

I apologize for failing to write with sufficient clarity, nor to
make clear that I was speaking to a generalized point not of your
specific airport.

If that is your point, I see no support for it whatsoever.

Yes, I know. As I said, we've had this discussion before.

Cheers,
Sydney

In article ,
(Michael) wrote:

Roy Smith wrote
I fail to see how this is relevant to the protection offered on
approach. The hazard on the approach into LVJ is a 1200 ft tower.
That tower is actually much CLOSER to the FAC on the GPS approach.

Why not call up the local tracon, ask to speak to the procedures guru,
and find out from somebody who is in a position to know for sure?

To know what for sure?

Why the approach was designed the way it was, how the TERPS rules were
applied, etc.

Maybe the approach really is broken and your pointing it out will get it
fixed. Maybe the tower is just charted in the wrong place and there's
really nothing wrong with the approach (I've see that before).

I've found problems with charts and reported them. They get fixed. If
people never report them, they stay broken. It's certainly interesting
to discuss is on usenet, but it's probably not an effective way to get
problems fixed.

Procedures used to be designed by the Region, but those offices were shut
down and the whole works moved to either Sacramento or Oke City, I can't
remember which. I learned a lot when I was able to pick up the phone and
talk to the designer of an approach I had questions about...but that is no
longer the case. To my knowledge, procedures were never designed by TRACONS.

Bob Gardner

"Roy Smith" wrote in message
...
(Michael) wrote:
I fail to see how this is relevant to the protection offered on
approach. The hazard on the approach into LVJ is a 1200 ft tower.
That tower is actually much CLOSER to the FAC on the GPS approach.

Why not call up the local tracon, ask to speak to the procedures guru,
and find out from somebody who is in a position to know for sure?

(Snowbird) wrote
Yes, I know. We've had this discussion before. It seems
obvious to me that it's relevant. In the case you cite,
apparently the GPS approach doesn't avoid the tower. However,
with a GPS, the capability to establish a waypoint at a
convenient spot clearly allows the approach designer to work
around terrain and obstructions in a way that an approach
based on one or two ground navaids can not.

And if the approach designer was (a) cognizant of the real world, and
not simply relying on rules (TERPS) and (b) was not constrained by the
need to expedite airline traffic at any cost to GA, this might even be
important. However, in the real world where neither (a) nor (b) is
true, I just don't believe it's an important factor.

If a VFR GPS is used to
back up the VOR approach, then I would argue that safety is increased
over the standalone GPS approach, since (a) the hazard is
significantly farther from the FAC and (b) a second source of
navigation, relying on a completely different signal source, is
available as a sanity check.

You may even be correct in this instance, but I don't think that
can be generalized

With respect to the first part, of course not. With respect to the
second (a completely different signal source) I absolutely do not
concur. In all cases, where a GPS is used in an overlay mode with the
underlying navaid still monitored, the underlying navaid, while in
general less accurate than the GPS, still provides a sanity check. A
standalone GPS approach lacks such a check in almost all cases.

This is particularly problematic due to the nature of the GPS signal.
It's quite unlikely that GPS (VFR or IFR) will be spoofed (whether
intentionally, or unintentionally due to signal reflections and/or
interference) in such a way as to cause a small error in position.
However, the underlying math of position determination by signal delay
from multiple sources of known position is such that it is possible to
spoof the device with a reflected signal in such a way as to cause it
to give reasonable track and speed information but a grossly erroneous
position. I've never actually seen a GPS do this (though I have seen
a math geek prove it's possible) but I HAVE seen LORAN do this.

Even a very low accuracy signal (such as a VOR 30 miles from the
field) will provide a crosscheck more than accurate enough to catch
such a problem. The same is not necessarily true of RAIM.

nor can it be generalized that the capabilies/
safety of IFR and VFR GPS are equal.

I understand some VFR GPS can be set to precise course guidance
(full deflection = 0.3 miles) and of course a VFR GPS can be
installed so as to have the same features of IFR GPS -- RAIM
prediction and monitoring, installed antenna etc. But many
are not installed or set up that way.

This is absolutely correct. IFR GPS provides a certain 'guaranteed'
level of performance. I put guaranteed in quotes because I don't find
the software methods used particularly impressive, and I used to write
similar software for a living before I became a manager and ceased to
do anything useful.

A VFR GPS provides whatever level of performance you wish to have and
are willing to pay for. However, even the highest level of VFR GPS
performance comes at a lower cost than the cheapest possible IFR GPS.

Michael

Bob Gardner wrote:
Procedures used to be designed by the Region, but those offices were shut
down and the whole works moved to either Sacramento or Oke City, I can't
remember which. I learned a lot when I was able to pick up the phone and
talk to the designer of an approach I had questions about...but that is no
longer the case. To my knowledge, procedures were never designed by TRACONS.

Bob Gardner

"Roy Smith" wrote in message
...

OKC. I have a friend working there now; matter of fact, he just
finished designing two approaches for an airport I frequent (*yay!*).
Their website is http://www.naco.faa.gov, and you're looking for the
National Flight Procedures Office. They can be reached at:
AVN-100
C. Fred Anderson, Manager
Phone: 405-954-3027
Fax: 405-954-4236

AVN-101
Bradley W. Rush, Assistant Manager
Phone: 405-954-0188
Fax: 405-954-4236

--Dave Buckles

http://www.flight-instruction.com

Roy Smith wrote
Why the approach was designed the way it was, how the TERPS rules were
applied, etc.

This is well known locally. The approach was designed the way it was
to keep from interfering with Hobby operations. A North/South
approach would be guaranteed to interfere with Hobby, which is just a
few miles almost due North of LVJ. There used to be such an approach,
and it was decomissioned for that reason.

Maybe the approach really is broken and your pointing it out will get it
fixed. Maybe the tower is just charted in the wrong place and there's
really nothing wrong with the approach (I've see that before).

The approach is not broken. Bob Gardner was nice enough to send me
the appropriate excerpt from TERPS (thanks Bob - but why didn't you
just post it?) and the tower is just outside the secondary area, and
thus not a factor. I simply did not know that there was no
requirement for the protected area to be large enough to contain
allowed instrument error and maximum allowable (by the PTS) deviation.
Now I do.

The tower is charted correctly - I know where it is, there is nothing
to check.

I've found problems with charts and reported them. They get fixed.

Yes, I've had the same experience. However, those were actual
charting errors. This is not one of them. The error was on my part -
I did not know what the actual protected area was like, and assumed it
was larger than it really was.

It was a little over a year ago that I had a similar learning
experience. I discovered that when an approach is temporarily NOTAM'd
NA, the plate is not so noted, even if the approach is NA for years.
So you have current plates, a standard briefing with NOTAM's, and
unless you specifically ask for Class II NOTAM's, you will never know
the approach is not available until you ask for it. The long and the
short of it is that most IFR pilots are not aware of this (nobody at
my home field was) but that's the way the system works. This is more
of the same - the system is working as designed, but most pilots are
not aware that this is proper. I did an informal survey at my home
field, and none of the IFR pilots (including an airline captain and a
DE) knew about this. I wondered then how many more gotchas there were
in the system. I'm still wondering.

I am not far from deciding that the system is so full of gotchas that
GA IFR is simply not a reasonable thing to do.

Michael

"Michael" wrote in message
m...

Bob Gardner was nice enough to send me
the appropriate excerpt from TERPS

TERPS is available as a PDF or photocopied images at
http://www.dot.state.fl.us/aviation/...ion/fedpub.htm

It's large (28 Mb) but interesting.

So you have current plates, a standard briefing with NOTAM's, and
unless you specifically ask for Class II NOTAM's, you will never know
the approach is not available until you ask for it.

Yes, the NOTAM system is still a mess, but it's a little easier to get the
published NOTAMs now that they're on line:

http://www1.faa.gov/NTAP/

Barry