Eric Greenwell wrote:
wrote:

No airspeed and/or altimeter training is essential.


I agree with this, but ...

From personal
experience (2000+ glider hours in both rental and private gliders) you
WILL eventually lose the use of either of these instruments inflight -
and it should be absolutely no big deal!


...suppose you always flew gliders with a redundant altimeter that read
AGL? Would it be proper for the pilot to refer to this during landing?
Would he be safer overall, even if his "that looks about right" skills
faded a bit?

A lot of us have this redundant, AGL readout altimeter in our cockpits
already: it's a PDA running a program like SeeYou or Winpilot.

I have two mechanical altimeters in my cockpit - one in feet - always set to QNH
on take off. Once away from the field, in accordance with the regulations that
gets set to 1013Mb and used to report altitude.

Being a metrically indoctrinated mathematically challenged and mentally limited
XC pilot. I have tried to find ways to use the second altimeter to make my XC
easier and safer.
My experience is that the other one is a great aid for it is a metres alti, and
is generally set at QFE of my launch point. (this one does go to zero even at
4740" MSL...)

This gives me my working height very easily.
Add or subtract the terrain difference of target from launch (usually negligible
where I fly)
Subtract the height we want above ground for safety.
Each Km on the metres altimeter is 1x whatever I have set my Mc to in range. If
you want to you can even move the secondary so that it shows your desired target
altitude as zero - removing the mental arithmetic. Easy, fast access to
information, no electronic dependancy.

So on a reasonable XC in my Cirrus it is very simple to get to 27km range from
1km working height. For a typical final glide to my home field that is
4740+1000+3300 feet = 9040" on QFE, but the typical winter pressure altitude is
off by +500 to -800" so my feet altimeter will be showing anywhere between ~8200
and 9500".

The PDA+LX20 then gives me a computerised reality check - (assuming that there
have been no electronics failures)If what it is saying, and what my mental
arithmetic is saying differ substantially I know it is time to be careful and
start checking to find the mistake. Having the second altimeter (metric or
imperial) means you have less mistakes to make. Having the second altimeter in
metres, improves safety - I am never confused as to what information it is
giving me. If the Altimeter says feet it is altitude - always. If it says metres
it is working height - always.

Caveats -
1] this does not work very well when there is a large pressure gradient across
the are you cover. This is why the GPS altitude is very useful as a check.
2] If you are flying in mountainous terrain, the feet altitude of the terrain is
more significant than the working height (this only works well when there is no
solid stuff in your "working height")
3] If you are more comfortable with miles, then this is not likely to help much.

On your comment of eventually meeting a situation where you do not have full
instruments.

For what it is worth - Even with a normal complement of two varios, two
altimeters and a GPS/PDA, I have once had the experience of zero working
instrumentation. LX20 in Slovenia for calibration + one standard issue large bug
in the static line == no vario, no ASI, no altitude, half way up the winch
launch. Landing a little over an hour later was a little more cautious than
normal, I would not have wanted to do this in a field. I did land a little fast
and about 100m further past the threshold for safety - you don't want to get
slow in the landing with an early Cirrus... Finding and extracting the bug was a
lot more work.