shon7,
Seeing as you mentioned the word "rain", Freezing Rain is considered as potentially the worst meteorological condition conducive to ice formation. Our company's operations prohibit takeoff in Freezing Rain.
Having said that, in conditions other than freezing rain, the temperature range from TAT +10°C to SAT -40°C is generally considered as 'the iceing range'. The upper limit (TAT +10°C) is indicative of skin temperature, and thus the upper temperature limit at which ice can adhere to the aircraft skin. The lower limit (SAT -40°C) is an atmospheric condition, as super-cooled water droplets can exist down to that temperature. At lower temperatures, any atmospheric water droplets will be frozen already (unless someone turns the thermal anti-ice ON, melts them, allowing re-freezing further aft on the wing, it's been done).
Some aircraft have SAT indicators, some TAT, and some both. Both is best, as the upper and lower limits can be accurately ascertained. Aircraft with RAT indicators, or only one of either SAT or TAT, must be examined by the manufacturer to provide information to the pilot of the 'adjusted' criteria pertinent to the aircraft installation and the speed range of the aircraft.
Not so sure of your formula arismount, (Ram Rise in Deg. C = TAS sqrd / 9500), it sounds about right if your speed is in Miles per Hour and you're using a Rosemount probe (Ct = 0.958). I think that you'll get better results if you use -
Rise (°C) = (TAS (Knots) / 87.1)^2,
OR
Rise (°C) = Absolute Temperature (°K) X 0.2 X Mach Number ^2
I agree with you Denti, it would be a good thing to have both TAT and SAT displayed, rather than burying one within the FMC.
Regards,
Old Smokey
Last edited by Old Smokey; 16th December 2005 at 14:54.