  A sample of 17 FR I radio galaxies constructed from the 3CR catalog, which is
characterized by edge-darkened radio structures, is studied. The optical core
luminosities derived from Hubble Space Telescope observation are used to
estimate the Eddington ratios which are found to be below $10^{-3.4}$ for this
sample. This is supported by the Baldwin-Phillips-Terlevich optical diagnostic
diagrams derived with the spectroscopic observation of Telescopio Nazionale
Galileo, suggesting that these sources are of low ionization nuclear
Emission-line Regions (LINERs). It implies that the accretion in these FR I
sources can be modeled as advection-dominated accretion flows (ADAFs). Given
the low accretion rate, the predicted jet power with a fast-spinning black hole
(BH) $a=0.95$ in the Blandford-Znajek mechanics is lower than the estimated one
for almost all the sources in our sample. Such powerful jets indicate the
presence of magnetically arrested disks (MAD) in the inner region of the ADAF,
in the sense that the magnetic fields in the inner accretion zone are strong.
Moreover, we show that, even in the MAD scenario, the BH spins in the sample
are most likely moderate and/or fast with $a\gtrsim0.5$.
