  Superconducting wires with broken time-reversal and spin-rotational
symmetries can exhibit two distinct topological gapped phases and host bound
Majorana states at the phase boundaries. When the wire is tuned to the
transition between these two phases and the gap is closed, Majorana states
become delocalized leading to a peculiar critical state of the system. We study
transport properties of this critical state as a function of the length $L$ of
a disordered multichannel wire. Applying a non-linear supersymmetric sigma
model of symmetry class D with two replicas, we identify the average
conductance, its variance and the third cumulant in the whole range of $L$ from
the Ohmic limit of short wires to the regime of a broad conductance
distribution when $L$ exceeds the correlation length of the system. In
addition, we calculate the average shot noise power and variance of the
topological index for arbitrary $L$. The general approach developed in the
paper can also be applied to study combined effects of disorder and topology in
wires of other symmetries.
