(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