particle physics - Neutrino flavor and mass eigenstates

Neutrions are produced and detected as flavor eigenstates $\nu_{\alpha}$ with $\alpha=e, \mu, \tau$. These states have no fixed mass, but are the combinations of three mass eigenstates $\nu_{k}$ with $k=1, 2, 3$, with mass $m_1$, $m_2$ and $m_3$, respectively. My questions are:

a) do neutrinos travel from source to the detector as flavor eigenstates or mass eigenstates?

b) is it possible to know which mass eigenstate the neutrino is in?