From: billd@ai.mit.edu (Bill Dally)
Newsgroups: rec.aviation.ifr
Subject: Dealing with Ice Safely
Date: 27 Jan 93 23:54:56 GMT
Article-I.D.: grits.BILLD.93Jan27155456
Distribution: usa
Organization: MIT Artificial Intelligence Laboratory
NNTP-Posting-Host: grits.ai.mit.edu
In-reply-to: 's message of Friday, 22 Jan 1993 00:57:08 EST

You can fly IFR in the Winter if you take care and always leave
yourself an out.  I know many pilots who will simply not fly in clouds
when the OAT is below 0C.  While I respect their decision, it can be
done safely if you watch the weather closely and handle any icing that
occurs quicly.  I am not giving any legal opinion here.  Rather the
following are some things I've learned flying many hours in forcast
and reported icing conditions mostly in a Twin Comanche, and a C-210.

First, you should get some icing experience in the model that you will
be flying.  

Next, for any given trip where you suspect ice, study the weather.
Not just freezing level and icing reports and forcasts, but also
ceilings and tops, surface temperatures and dewpoints, and frontal
system positions.

Finally, during the trip, have a plan that includes what to do if you
encounter ice and contingency plans for what to do if it is worse than
you were planning on.  All of these plans should terminate with you
safely on the ground.

For the training, find a good CFII who will go up with you on a day
with light to moderate ice forcast and a freezing level well above the
ground.  Get familiar with where it forms on your plane, how fast it
forms (although this will vary with conditions), how fast it comes off
(on top in the sun or below the freezing level), and most importantly
how your plane handles (especially rate of climb and stall speed) with
a load of ice.  Practice a few landings with small amounts of ice on
the plane.  Hearing or reading about ice won't do it.  To be
comfortable flying you have to get some experience and you don't want
to do it by yourself.  (If you haven't flown in ice before, beware of
what this will do to the paint on the leading surfaces of your plane.)

Beware that the way planes handle with ice is very specific to model.
The 210 with its big fat wing was much more tolerant of ice than my
Comanche with its laminar flow wing is.  Also, the amount of excess
horsepower you have is a big factor in continuing flight with a load
of ice or being able to climb out of it.

To convert the weather information to a go-no-go decision here are
four things I consider:

1.  Any chance of encountering severe icing or freezing rain is an
automatic no-go.  I had one encounter with unforcast freezing rain in
my old 210 and I don't want to attempt a second.  The rental car
companies and commercial airlines have gotten much business from me on
this one.

2.  Reports (not forcasts) of light to moderate icing disqualify altitudes
for the enroute portion of the flight.  However, with care you can
climb or descend through them.  In my Twin Comanche I can climb at
better than 2000FPM at typical gross weights (not MAX) and METO power
(28", 2600).  This gets me through many icing layers in less than a
minute.  I have found that moderate ice won't accumulate to
significant amounts in this amount of time.  If you can get on top on
a sunny day, it comes off pretty fast.  

Coming down, let ATC know that you want no delay to an altitude below
the icing.  They will generally accomodate you.  If necessary use the
speed brakes (also known as landing gear).  If ATC suggests holding in
the middle of the icing layer the word "unable" comes in handy.
Beware that unless the surface temperature is above freezing, any ice
you pick up on the way down will be with you for landing.

You don't want to cruise in any form of icing.  Even if it seems to be
so light that it is sublimating off as fast as its forming, the rate
of formation can change rapidly.  This is one reason why I fly a plane
with turbochargers and O2.

3.  If the surface temperature in the location of the icing is within
a few degrees freezing, I consider well-documented moderate icing to
be a no-go.  This is where checking the surface temperatures and
correlating them with the freezing level is important.  I had one
flight in my 210 from AUS (Austin TX) back to BED (Bedford MA) that
ended with a diversion to ORH (Worcester MA) when I discovered that the
freezing level wasn't at 6000 like the briefer said, but was really
at the surface.  The surface temperature at ORH was 34.

4.  Low ceilings are another complicating factor that makes me derate
moderate icing.

After you've gotten the `official weather' ask anyone who just landed
what they encountered.  This is particularly important if there is a
chance of ice on the climb out.  In addition to pilots in a lounge or
tying down planes, you can also call the corporate/commercial guys on
the radio. Most ground controllers don't mind if you ask them to ask
the King Air that just landed to call you on 122.95 and most of the
time the King Air will call.

From the weather report you will have an expectation about where you
might encounter ice.  You will be expecting at most moderate icing on
either the climb out or the descent (enroute ice is a no-go).  Most of
the time, things will be better than you expect.  Most weather
briefers are *very* pessimistic.  Most of the time when I'm expecting
some ice I don't get any at all.  A few other times I will get what
I'm expecting, a light coat of ice (often hard to see) on the leading
edges of things which comes off quickly once I'm on top.

However, after you takeoff, things sometimes don't go according to
plan.  The two rules I keep in mind are (1) get out of the ice ASAP
and if I get more than 1/4 inch, (2) get on the ground ASAP.

1.  You takeoff and encounter an icing layer at 6000.  From the
weather report, you are expecting to be on top at 8000 and so have
filed for 10.  Unfortunately at 10 you're still in the soup and still
picking up light ice.  Remember thay you will usually pick up as much
going down as you did going up, so don't wait too long before you
apply rule 2 and make the 180.  I have had this happen to me numerous
times and have become very skeptical of reports on cloud tops.

2.  You encounter unforcast enroute icing.  This usually happens to me
when I'm flying West and don't want to buck the 70KT headwind at
18000.  The solution is always an altitude change, but the direction
depends on (1) how far you are from the freezing level and (2) what
sort of icing you are getting.  Unless you can get below the freezing
level quickly, go up and if possible get on top.  If you hit freezing
rain, (recognizable by the frozen droplets on the windshield)
definitely go up.

Once on a leg from 3SG (Saginaw MI) to EAU (Eau Claire WI) I
encountered some light ice at 8000 (the freezing level was supposed to
be 12).  It was right at freezing so I asked to go down.  Minneapolis
Center kindly informed me -- "unable ... opposite direction traffic
... expect lower in 10 minutes".  This is where familiarity pays.  It
actually took 5 minutes and I had accumulated less than 1/8 inch by
that time.  It all came off quickly at 6000.

3.  You encounter more ice than you expect on the way down.  First,
remember that the weather report you got four hours ago is old news by
now, so call flight watch before you start down.  (You should have
been calling them every hour anyway to get the destination SA and
PIREPS if there was any question about it).  If they have reports (not
forcasts) of moderate or severe icing -- go somewhere else.

If there are no reports of moderate or severe, plan a normal descent.
If you unexpectedly get your windshield plastered, the decision to
make is (1) go back up where its sunny and find somewhere else to land
or (2) continue to your original destination, or (3) divert to a
closer destination.  This depends on how much fuel you have, how high
you are above the freezing level or the surface, how far below the
tops you are, and how fast the ice is accumulating.  My decision is
usually either (2) or if I exceed 1/4 inch, (3) (as in the diversion
to ORH above).

In summary, the utility of an IFR-equipped plane is greatly enhanced
if you are able to fly it in clouds in the winter.  To do this safely
you should (1) get training from someone with *lots* of experience,
(2) get all the weather information you can and make an educated
go-no-go decision, and (3) have a plan for what to do if things aren't
as expected.

Bill Dally			CP-AMEL/IA
billd@ai.mit.edu		Twin Comanche N8431Y

PS.  I do respect the pilot who refuses to fly in clouds below 0C.
Some people think I'm too conservative for not flying single-engine
IFR anymore after what happened to my 210 (that's another story).




--
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  /___Bill
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billd@ai.mit.edu
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