Bob Gardner
March 6th 06, 01:28 AM
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.
>
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.
>