hi again,
selecting a v/s is another way of reducing your climb thrust which equals to a derated climb.
however its mentioned in the book to enter the derate on the climb page of the mcdu. theres no mention of a v/s selection.
we noramlly use v/s to maintain the minimum climb required with maximum thrust. this is on the 343's where the at high wieghts the minimum climb can not be acheived.
bye.