Kilo Charlie wrote:

Maybe we're mixing things up a bit. I agree that knowing if I can make a
glide into a landable place is a good thing and the SN-10 does that. I
would still say given that, you should be looking outside to see what
mountains you need to go around in order to get there is a better idea than
looking at an instrument heads down.

The terrain warning doesn't require you to stare at the PDA, anymore the
Ilec requires you to stare at it. Just glance at it, see the red square
indicating the place where your glide slope is too low, and by how much.
Go back to looking out the window while you decide how to get around or
over the obstacle.

Also I would not find the instrument
much help unless it could calculate the required deviation from my current
position around the mountain then home.

That would be ideal, and I've suggested it to SeeYou, but it's not been
implemented. Maybe the next release. In the meantime, I've found the
warning is more useful than no warning.

At least for me I would not want to
leave my margins flying in the mountains so thin that I could just clear a
pass.

SeeYou uses a "clearance" altitude above the ridge equal to the
"arrival" height chosen for getting to a landing place. I usually use
1000 feet. So, when the red square first appears, it means my projected
glide slope is 999 feet above the terrain.

Finally all of the instrument manufacturers that feature terrain maps state
emphatically that they should NOT be used as terrain avoidance instruments.
My guess is that is due to the inaccuracies of the terrain altitude data.
I'm not willing to bet my life on that.

Did anything I said sound like I was flying with my eyes closed? The
pilot must use his judgement about reaching a landing place, whether
there is a mountain between it or not. I'm sure you don't head for a
landing place over a national forest at a zero McCready setting, just
because the Ilec says you are 50 feet above glide slope. Come on, give
us PDA users some credit.

--
Eric Greenwell - Washington State, USA
Change "netto" to "net" to email me directly

"Transponders in Sailplanes" on the Soaring Safety Foundation website
www.soaringsafety.org/prevention/articles.html

"A Guide to Self-launching Sailplane Operation" at www.motorglider.org