Eng anti ice and performance
 

If engine anti ice is required for departure then you apply a flex penalty for the airbus. If no penalty applied due to conditions and then in the climb out below 1500ft you then have to switch it on, does this not mean that you no longer have required performance if you have an engine failure? Would appreciate any help.

Yes.

(however flex thrust does have a margin in our favour, to do with the actual temperature giving more favourable conditions than the 'pretend' flex temp, see elsewhere on this forum)

We need to account for EAI if it is likely we will need it below 1500' (or the acceleration altitude, if higher).