Thanx for that, but it is still not very clear. According to the AFM, the WTAI is supposed to come on when you have MCT on the good engine and you are into your third climb segment so to speak. Also, suppose you have already taken into account the weight penalty of the engine and wing anti-ice on the performance calculations and the ATOW is at or below that. Accoding to the FAR part 25.111 (d)(2) ... the W1 and power/thrust must be constant throughout each segment; by putting the WTAI you are effectively reducing your available thrust by approximately 3% N1, give or take some.
One opinion that was given to me, was that since the FAR legal second segment had been complied with, you could put it on as only a 1.2% gradient was needed after 400 feet AGL (FAR Part 25.111 (c)(3)).
Now, I still think that since the Operator's acceleration altitude is set at 1500 feet AGL, you cannot afect the thrust till reaching that that altitude regardless of the FAR minimum legal 400 feet altitude. Is that correct or not?