wrote in message
oups.com...
Looks as if I'm missing something central here, as usual

Could be.

If there is a 4-hour flight that passes over some 10 waypoints and if
the FMGS keeps getting data that's off by 50 meters or so, am I to
understand that the aircraft will still make heading changes, etc.
that'd be in accordance with the programmed flight plan and that none
of the waypoints will be missed or indeed the final destination
precisely arrived at?

That is correct. The presumed 50 meter accuracy is constant throughout the
flight. It's not as though it's additive for each waypoint (or worse, as a
continuous function along the flight). Though frankly, even if it were,
you'd only be off by 500 meters after 10 waypoints which is still "no big
deal".

That's one of the many nice things about GPS. It is a continuous readout of
one's current position and any forward-looking navigation solution can be
derived from the instantaneous position information, without any previous
position information affecting the future calculations.

And of course, again...being 50 meters off in aviation just isn't that big
of a problem. Heck, being a mile off in aviation isn't that big of a
problem most of the time.

And someone mentioned an acceptable accuracy of 0.1 foot in property
surveying. If surveyors in my industry had that much latitude, there'd
be a lot of equipment skids that'd get installed quite inappropriately,
with lots of patched modifications thereon

Well, as that poster pointed out, it depends on the situation. But property
surveying for non-commercial purposes isn't likely to be used for any sort
of actual construction (except possibly locating a building, and for sure no
one is going to care if a building is off one inch one direction or another,
especially in a non-commercial situation).

As for equipment skids and such, since I don't know the details of your
industry I can't really comment on that. But it seems to me that if you
require that level of detail and are using GPS to accomplish it, you must be
dealing with positioning these skids at a significant distance from wherever
they are referenced to. Otherwise, I'd think one would use more
"conventional" surveying techniques to determine position, orientation, etc.

The only surveys I've ever hired were strictly property surveys, in which
property boundaries are determined, locations of roads, trees, terrain
contours, etc. Getting the results to within an inch is perfectly
sufficient for that type of survey. It's not hard to imagine a wide variety
of surveys for which the same holds true.

Just because some situations demand higher precision, that doesn't mean all
situations do.

Pete