John R. Copeland
March 5th 06, 10:38 PM
"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.
>
You are carrying a serious delusion about temperature inversions.
The atmosphere can stray *very far* from "normal" lapse rates.
Many times, I have seen multiple freezing levels (3 or more!)
between the surface and 12000 feet or so.
I have seen liquid precipitation falling through these multiple layers,
giving freezing rain over *multiple* altitude ranges.
Be sure you know what temperature profiles you'll be trying to climb through,
before you ever launch into the kind of conditions you've described.
I'm not quarrelling with your "standard strategy" though.
Please take this as an *addition* to your rules, not as a replacement.
>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.
>
You are carrying a serious delusion about temperature inversions.
The atmosphere can stray *very far* from "normal" lapse rates.
Many times, I have seen multiple freezing levels (3 or more!)
between the surface and 12000 feet or so.
I have seen liquid precipitation falling through these multiple layers,
giving freezing rain over *multiple* altitude ranges.
Be sure you know what temperature profiles you'll be trying to climb through,
before you ever launch into the kind of conditions you've described.
I'm not quarrelling with your "standard strategy" though.
Please take this as an *addition* to your rules, not as a replacement.