  We study an inhomogeneous coagulation equation that contains a transport term
in the spatial variable modeling the sedimentation of clusters. We prove local
existence of mass conserving solutions for a class of coagulation kernels for
which in the space homogeneous case instantaneous gelation (i.e., instantaneous
loss of mass) occurs. Our result holds true in particular for sum-type kernels
of homogeneity greater than one, for which solutions do not exist at all in the
spatially homogeneous case. Moreover, our result covers kernels that in
addition vanish on the diagonal, which have been used to describe the onset of
rain and the behavior of air bubbles in water.
