  Liquid drops can be kept from touching a plane solid surface by a gas stream
entering from underneath, as it is observed for water drops on a heated plate,
kept aloft by a stream of water vapor. We investigate the limit of small flow
rates, for which the size of the gap between the drop and the substrate becomes
very small. Above a critical drop radius no stationary drops can exist, below
the critical radius two solutions coexist. However, only the solution with the
smaller gap width is stable, the other is unstable. We compare to experimental
data and use boundary integral simulations to show that unstable drops develop
a gas "chimney" which breaks the drop in its middle.
