  We calculate the dynamical response of two-layer Josephson arrays to a bias
current applied into only one layer (primary layer), in a perpendicular
magnetic field. The pancake vortices in the two layers sometimes form into flux
lines which move as a unit under the influence of the bias current. The lines
break apart into independent pancakes in sufficiently high currents,
sufficiently weak interlayer coupling, or possibly sufficiently high fields. We
discuss the relevance of these results to recent experiments in high-T$_c$
superconductors in the flux transformer geometry.
