The ferroelastic symmetry changes of the lead-based complex perovskite PbFeY_0.5Ta_0.5O₃ are investigated by means of single crystal x-ray diffraction and observations in polarized light microscopy at different temperatures. The position of the 400 and 222 cubic reflections is followed between 80 K and 300 K. Results indicate the presence of two structural transitions at about 270 K and 220 K. Such temperatures define the stability range of three different phases. The high-temperature phase (T > 270 K) is the optically anomalous paraelectric prototype, the optical symmetry of which is uniaxial (tetragonal) in spite of the diffractometric (pseudo)cubic symmetry. The intermediate derived phase (270 K > T > 220 K) is tetragonal. This tetragonal phase coexists with a monoclinic one for 220 K > T > 200 K. Below 200 K only the monoclinic phase is stable. The (pseudo)cubic-to-tetragonal transition seems to be of the second order. The tetragonal-to-monoclinic one is of the first order.