Guerro, PantLoad, Mansfield, interesting stuff.
I suspect that TAT is displayed to the pilot on modern flight decks because it is always a consideration, and SAT has to be sought out (or calculated) because current research and a review of accidents place a question mark over the -40C 'rule'.
Interesting that it still exists in a current revision of an Airbus FCOM -- not indulging in type-bashing, but a recent revision date does not necessarily guarantee the latest thinking -- just the freshest sheet of paper!
The
Icing Branch at NASA Glenn Research Centre will tell you that icing is
more likely at SAT between +10ºC to -20ºC, but they
won't go so far as to say that temperatures below -40ºC do not require airframe or engine anti-ice.
The FCOM for our reasonably new Long Beach "twinjet", Supplemental Procedures, says (my bolding):
ADVERSE WEATHER PROCEDURES (Continued)
At temperatures below -20ºC (-4ºF), icing conditions should be less severe. However, heavy icing has, on occasion, been reported at temperatures as low as -60ºC (-76ºF)
Minus sixty
Originally Posted by Mansfield
Finally, none of this addresses the relatively newly understood issue of ice crystals, which are not part of the SAT less then -40C model at all, and seem to have had some success in instigating rollbacks, etc.
Probably the reason the "icing conditions do not exist where SAT ≤ -40ºC" advice was
removed from the BAe146 MoM.