  Inspired by the atmospheric multi-GeV neutrino data, we consider neutrino
flavor mixing matrices which are maximal in a $2\times 2$ subsector. This
condition is a strong restriction: the full matrix including complex phases
depends essentially on one parameter. The survival probability is an universal
function of $L/E$, independent of generation, in the region of interest for the
accelerator and atmospheric experiments. It is possible with the solar neutrino
data alone to recover completely the mixing matrix suggested by the atmospheric
data. The results are not essentially modified by the MSW effect in the solar
data. Consequences for future experiments are considered.
