Folks,
There are several things here.
(1) Do what the airframe manufacturer says in Limitations.
(2) Using engine anti-ice below -40C will not do any harm, just a possible but very minor loss of thrust --- and in some types you will have auto-ignition by whatever name on -- might be a plus.
(3) There are big temperature changes around Cb/Ts, just because you "were" experiencing temps. of less than -40C, doesn't mean you can't run into a wall of rising warm (relatively speaking) air.
Summary:
If you have the slightest doubt, and no limitations will be exceeded, ENG. ANTI ICE --- ON.
Tootle pip!!
Last edited by LeadSled; 11th Sep 2011 at 08:37.