  The structure of the three-body $nn\Lambda$ system, which has been observed
recently by the HypHI collaboration, is investigated taking $\Lambda N-\Sigma
N$ coupling explicitly into account. The $YN$ and $NN$ interactions employed in
this work reproduce the binding energies of $^3_{\Lambda}$H, $^4_{\Lambda}$H
and $^4_{\Lambda}$He. We do not find any $^3_{\Lambda}n$ bound state, which
contradicts the interpretation of the data reported by the HypHI collaboration.
