For those flying on the bus, FCTM says to turn Engine Anti Ice ON when flying near CBs even if TAT is <-40°c ! that's mainly because of ice particle icing (e.g. in an anvil).
Is there are more current version of the FCTM, or was that a Typo?
FCTM 04.010... (A320) July 2008 Version
FCTM 5.10.5... (A330, A340) 2006 Version
"...CLIMB/ DESCENT
Whenever icing conditions are encountered or expected, the engine anti-ice should be turned on. Although the TAT before entering clouds may not require engine anti-ice, flight crews should be aware that the TAT often decreases significantly, when entering clouds.
In climb or cruise, when the SAT decreases to lower than -40 °C, engine anti-ice should be turned off, unless flying near CBs..."
Also.....
FCOM 3.4.30 (Rev 39)
"...icing conditions may be expected when the OAT (on ground and for take-off), or when the TAT (in flight) is at or below 10 c, and there is visible moisture in the air (such as clouds, fog with low visibility of one mile or less, rain, snow, sleet, ice crystals) or standing water..."
Could we say the same for flying trough ICE crystals?
Someone had mentioned earlier that the query related to Boeing, thus the "Boeing Bulletin" would apply. But, it's interesting to note that Airbus seems to agree (...Ice Crystals...).
Like some other examples between the two, Airbus says "do this, don't do that," Boeing tells you why.