(Michael) writes:

But think for a second - why do you suppose MEA's and OROCA's provide
1000 ft of obstacle clearace normally, but 2000 in designated
mountainlous areas?

That's exactly why, of course.

If you're IFR, you're not going to be clearing that peak by less
than 2000 ft, and that is going to keep you out of the rocks in even
the worst case scenario. If you're VFR, then you can see the peak
and don't really need the altimeter anyway.

That's what one would hope. Unfortunately, there are many gradations
between CAVU and IMC, and pilots do seem to have an unfortunate
tendency to fly into mountains or get stuck in canyons from time to
time while (legally) VFR.

The most interesting result of WAAS, I think, will be its educational
effect on pilots. Right now, I often see postings from people who
think they can use their altimeters to check the vertical accuracy of
their GPS's. At cruise altitude, the GPS is likely to be by far the
more accurate of the two even without WAAS (though obviously we need
to stick with the altimeter to ensure separation). Near to the
ground, as you mention, the altimeter may become the more accurate of
the two, assuming that you have the latest altimeter setting for the
field.


All the best,


David