  We consider the minimum-time problem for a multi-input control-affine system,
where we assume that the controlled vector fields generate a non-involutive
distribution of constant dimension, and where we do not assume a-priori bounds
for the controls. We use Hamiltonian methods to prove that the coercivity of a
suitable second variation associated to a Pontryagin singular arc is sufficient
to prove its strong-local optimality. We provide an application of the result
to a generalization of Dubins problem.
