  Homogeneous time-dependent solutions of massive gravity generalise the plane
wave solutions of the linearised Fierz-Pauli equations for a massive spin-two
particle, as well as the Kasner solutions of General Relativity. We show that
they also allow a clear counting of the degrees of freedom and represent a
simplified framework to work out the constraints, the equations of motion and
the initial value formulation. We work in the vielbein formulation of massive
gravity, find the phase space resulting from the constraints and show that
several disconnected sectors of solutions exist some of which are unstable. The
initial values determine the sector to which a solution belongs. Classically,
the theory is not pathological but quantum mechanically the theory may suffer
from instabilities. The latter are not due to an extra ghost-like degree of
freedom.
