Stable hyperplane arrangements

We classify complex hyperplane arrangements $\mathcal A$ whose intersection posets $L(\mathcal A)$ satisfy $L(\mathcal A)=\pi_i^{-1}\circ\pi_i\bigl(L(\mathcal A)\bigr)$ for $i=1,\dots,n$. Here $\pi_i$ denotes the projection from $\mathbb C^n$ onto $\mathbb C^{n-1}$ defined by that forgets the coordinate $x_i$ of $(x_1,\dots,x_n)\in\mathbb C^n$, and $\pi_i\bigl(L(\mathcal A)\bigr)=\{\pi_i(S)\mid S\in L(\mathcal A)\}$. We show that such arrangements $\mathcal A$ arise as pullbacks of the mirror hyperplanes of complex reflection groups of type $A$ or $B$.