  We construct and study several semilocal density functional approximations
for the positive Kohn-Sham kinetic energy density. These functionals fit the
kinetic energy density of the Airy gas and they can be accurate for integrated
kinetic energies of atoms, molecules, jellium clusters and jellium surfaces. We
find that these functionals are the most accurate ones for atomization kinetic
energies of molecules and for fragmentation of jellium clusters. We also report
that local and semilocal kinetic energy functionals can show "binding" when the
density of a spin unrestricted Kohn-Sham calculation is used.
