  Coronal mass ejections (CMEs) are closely related to eruptive filaments and
usually are the continuation of the same eruptive process into the upper
corona. There are failed filament eruptions when a filament decelerates and
stops at some greater height in the corona. Sometimes the filament after
several hours starts to rise again and develops into the successful eruption
with a CME formation. We propose a simple model for the interpretation of such
two-step eruptions in terms of equilibrium of a flux rope in a two-scale
ambient magnetic field. The eruption is caused by a slow decrease of the
holding magnetic field. The presence of two critical heights for the initiation
of the flux-rope vertical instability allows the flux rope to stay after the
first jump some time in a metastable equilibrium near the second critical
height. If the decrease of the ambient field continues, the next eruption step
follows.
