Let M be a closed,
connected, smooth and 3-connected mod2 (i.e. Hi(M;Z2) = 0,0 < i ≤ 3)
manifold of dimension 3 + 8k with k > 1. We obtain some necessary and sufficient
condition for the span of a (3 + 8k)-plane bundle η over M to be greater than
or equal to 7 or 8. We obtain, for M 4-connected mod2 and satisfying
Sq2Sq1Hn−8(M) =Sq2Hn−7(M), where n =dimM ≡ 11mod16 with n > 11,
that span M ≥ 8 if and only if χ2(M) = 0. Some applications to product manifolds
and immersion are given.