Fe1
This site has 3 4-fold rotation axises.So both the x, y and z axes can be chosen as the z-axis of a PAS and the EFG tensor vanishes here.
Fe2
The axis trough the Fe2a and the N site is a 4-fold rotation axis, the two axises perpendicular to this one are only 2-fold rotation axises. The axis trough the Fe2a and N site can thus be chosen as the z-axis of a PAS where eta=0 but EFG does not vanish.