LFBV servo current must be greater 30% and liquid fuel flow must be less than 3%. these two logics are configured in parallel for Pre-ignition trip (L4PRET) in Mark-VI control.

What is the necessity of these logics?

 

First, to ensure the liquid fuel control valve is not trying to admit fuel flow to the turbine prior to starting, and second, to ensure there is no fuel flowing to the turbine prior to starting.