  Supra-arcade fans are bright, irregular regions of emission that develop
during eruptive flares, above flare arcades. The underlying flare arcades are
thought to be a consequence of magnetic reconnection along a current sheet in
the corona. At the same time, theory predicts plasma jets from the reconnection
site which would be extremely difficult to observe directly because of their
low density. It has been suggested that the dark supra-arcade downflows (SADs)
seen falling through supra-arcade fans may be low density jet plasma. The head
of a low density jet directed towards higher density plasma would be
Rayleigh-Taylor unstable, and lead to the development of rapidly growing low
and high density fingers along the interface. Using SDO/AIA 131A images, we
show details of SADs seen from three different orientations with respect to the
flare arcade and current sheet, and highlight features that have been
previously unexplained, such as the splitting of SADs at their heads, but are a
natural consequence of instabilities above the arcade. Comparison with 3-D
magnetohydrodynamic simulations suggests that supra-arcade downflows are the
result of secondary instabilities of the Rayleigh-Taylor type in the exhaust of
reconnection jets.
