Are you familiar with Skew-T diagrams? They show a continual track of
temperature and dewpoint versus altitude as reflected by the RAOB balloon.
Might be better than depending on rules of thumb. Just Google Skew-T and you
will get plenty of links.

Bob Gardner

"Peter" wrote in message
...
I would like some feedback here from experienced IFR pilots.

This is concerning practical issues, not regulatory issues which in
any case vary according to country (I am not in the USA).

I am an FAA PPL/IR and fly a TB20, not de-iced except for a TKS prop.

My standard strategy for flight in potential icing conditions
(potential IMC, with TAT between 0C and about -15C) could be
summarised as follows:

No flight if embedded TCU/CB activity forecast

No flight if the forecast 0C level is below the MSA (MOCA) plus
1000ft, unless the potentially freezing layer can be clearly
established as less than say 2000ft thick (a current skew-t, or
looking up through the holes) and one can fly VMC on top without
problems with controlled airspace etc.

No flight if the potentially freezing layer is thicker than about
5000ft (this one needs a solid escape route, 2000ft or so of warm air
below and preferably over the sea.

I've picked up ice at various times, up to about 1cm, without
problems. The TKS prop also keeps the front window clear.

Now, the question is about freezing rain.

Speaking to instructors/examiners, the FAA oral/written position seems
to be that since there must be warmer air above, one should CLIMB.

However, it seems to me that this must depend on the severity of the
temperature inversion, and where on the temperature/height curve one
is flying.

1) Let's say the TAT is -2C - a descent of only 1000ft+ should take
care of it using the conventional escape route, but not if one is
flying just below the top of the inversion in which case the
temperature would get lower still upon descent.

2) Let's say the TAT is -8C - this seems a poor position to find
oneself in, but could one encounter freezing rain at a SAT of say
-10C? Would it not be snow or sleet? What is the realistic SAT range
for freezing rain?

Any suggestions will be much appreciated.

I've been in rain just above TAT=0C, and when the TAT dropped to 0C I
always descended some 2000ft and that always took care of it. In
European airways flight one is typically at FL120 and there is nothing
below in *most* places so this is an obvious way out.