From: aboyd@quantum.on.ca (Andrew Boyd)
Subject: Re: Talk about an unusual "field"!
Date: Thu, 19 Nov 92 16:04:32 GMT
Organization: Quantum Software Systems

In article <1992Nov19.041749.7777@netcom.com> rkaplan@netcom.com 
(Richard Kaplan) writes:
>... the "field" is 3000 feet of ice on a plowed lake.
>
>My intuitive feeling is that the landing roll for a C-172
>on ice is unknown and therefore this type of operation
>should not be attempted without extensive prior experience
>or an extremely long and wide "field" (neither of which will be 
>present in this case).  The minimal friction on landing
>could present problems regarding both length of the
>landing roll and directional control.

agreed, extra runway length is never a bad thing ... the question
is whether or not you'll need it :)  

A rule of thumb I use is that, if you touch down at 50 MPH (C-172
full stall), down to 25 MPH (1/2 your touchdown speed), aerodynamic 
braking is far more important than your wheel brakes.  After all,
even on pavement, at 40 MPH your wings are still developing a lot
of lift, and without downward force, your tires will simply skid
if you touch the brakes at 40 MPH.  For the same reason, you don't
use your brakes to stay straight at 40 MPH (at least I don't), you
use rudder.

So, we're going to do a full-stall landing, 1.3 Vso approach speed,
with full flaps for maximum aerodynamic braking.  After we get down
to 25 MPH, then we have to deal with the ice problem - we may not
have any friction whatsoever if the ice is really smooth.

Pretend you're in your car at 25 MPH, and you drive onto glare ice.
Could you keep straight?  Could you come to a stop?  If you don't
feel comfortable with that scenario, don't land your a/c on ice.

A few times every year, our 4000' x 75' paved runway at CYSH ices up
like a skating rink, and once you get used to it, it's not so bad.

As far as keeping directional control, the a/c has inertia straight
down the runway ... what is going to disturb it?  Obviously, wind
is a biggie.  You probably will not feel very comfortable with much
crosswind component on ice, especially if it is gusty!

What I do with the C-172 on ice with x-wind is to land the a/c crabbed.
As long as the runway is completely iced (bare patches are not good
for this technique) and the wind is steady, you will be ok.  If you
start to drift downwind, rudder into the wind, add power if necessary.
If you start to drift upwind, rudder out of the wind.

>Our fellow pilot feels that even though he hasn't done
>this before, he is capable of doing so since (1) "rotational
>friction" will be sufficient to stop the aircraft (2) he is
>proficient at short field technique (3) directional control
>will not be necessary if the approach velocity vector is
>aligned with the landing surface.

He's mostly correct ... the question is whether or not is he correct
enough to avoid bending any metal.  Like anything different in 
flying, it is cheap insurance to have an experienced instructor
in the right seat the first time you land on ice.  And I don't
mean any zit-faced kid with a fresh CFI ticket who only flies
C-150s off pavement until he can get into a boeing - find an
instructor who is experienced in landing on ice.  Look for
an instructor who owns his own a/c, and usually has thousands
of hours & decades of experience in his logbook.  

Couple of other important points ... just like any off-airport
landing, how is the runway surface?  Ice may buckle, or form
very hard wind drifts that may be almost impossible to see.
Those yellow high-acuity sunglasses can help a lot to spot
drifts.

And for god's sake, how thick is the ice?  

How long has it been below freezing?  Any recent thawing, which
might form slush?  Slush will greatly extend your takeoff run,
and can do terrible things to moving parts (eg brakes, retractable gear)
when it freezes at the colder temps aloft.

If other a/c are using the surface, evidence would suggest the
surface is ok, with proper technique.  Just one more tip: use
the same portion of the runway as the other a/c: other areas
of the surface may hold expensive surprises for you.

Have fun!
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