  Supra-arcade downflows (SADs) are sunward, generally dark, plasma density
depletions originated above posteruption flare arcades. In this paper using 3D
MHD simulations we investigate if the SAD cavities can be produced by a direct
combination of the tearing mode and Kelvin-Helmholtz instabilities leading to a
turbulent current sheet (CS) medium or if the current sheet is merely the
background where SADs are produced triggered by an impulsive deposition of
energy. We find that to give account of the observational dark lane structures
an addition of local energy, provided by a reconnection event, is required. We
suggest that there may be a closed relation between characteristic SAD sizes
and CS widths that must be satisfied to obtain an observable SAD.
