The space of inessential bounded linear operators from one Banach space $X$ into another $Y$ is introduced. This space, $I(X,Y)$, is a subspace of $B(X,Y)$ which generalizes Kleinecke’s ideal of inessential operators. For certain subspaces $W$ of $I(X,Y)$, it is shown that when $T\in B(X,Y)$ has a generalized inverse modulo $W$, then there exists a projection $P\in B\left(X\right)$ such that $T(I-P)$ has a generalized inverse and $TP\in W$.

In addition to Pisier’s counterexample of a non-accessible maximal Banach ideal, we will give a large class of maximal Banach ideals which are accessible. The first step is implied by the observation that a “good behaviour” of trace duality, which is canonically induced by conjugate operator ideals can be extended to adjoint Banach ideals, if and only if these adjoint ideals satisfy an accessibility condition (theorem 3.1). This observation leads in a natural way to a characterization of accessible...