  A model is presented in which both Fanaroff and Riley class I and II
extragalactic jets are produced by magnetized accretion disk coronae in the
ergospheres of rotating black holes. While the jets are produced in the
accretion disk itself, the output power still is an increasing function of the
black hole angular momentum. For high enough spin, the black hole triggers the
magnetic switch, producing highly-relativistic, kinetic-energy-dominated jets
instead of Poynting-flux-dominated ones for lower spin. The coronal mass
densities needed to trigger the switch at the observed FR break power are quite
small ($\sim 10^{-15} g cm^{-3}$), implying that the source of the jet material
may be either a pair plasma or very tenuous electron-proton corona, not the
main accretion disk itself.
  The model explains the differences in morphology and Mach number between FR I
and II sources and the observed trend for massive galaxies to undergo the FR
I/II transition at higher radio power. It also is consistent with the energy
content of extended radio lobes and explains why, because of black hole
spindown, the space density of FR II sources should evolve more rapidly than
that of FR I sources.
  If the present model is correct, then the ensemble average speed of
parsec-scale jets in sources distinguished by their FR I morphology (not
luminosity) should be distinctly slower than that for sources with FR II
morphology. The model also suggests the existence of a population of
high-redshift, sub-mJy FR I and II radio sources associated with spiral or
pre-spiral galaxies that flared once when their black holes were formed but
were never again re-kindled by mergers.
