  Recent quasar surveys have revealed that supermassive black holes (SMBHs)
rarely exceed a mass of $M_{\rm BH} \sim {\rm a~few}\times10^{10}~M_{\odot}$
during the entire cosmic history. It has been argued that quenching of the BH
growth is caused by a transition of a nuclear accretion disk into an advection
dominated accretion flow, with which strong outflows and/or jets are likely to
be associated. We investigate a relation between the maximum mass of SMBHs and
the radio-loudness of quasars with a well-defined sample of $\sim 10^5$ quasars
at a redshift range of $0<z<2$, obtained from the Sloan Digital Sky Surveys DR7
catalog. We find that the number fraction of the radio-loud (RL) quasars
increases above a threshold of $M_{\rm BH} \simeq 10^{9.5}~M_{\odot}$,
independent of their redshifts. Moreover, the number fraction of RL quasars
with lower Eddington ratios (out of the whole RL quasars), indicating lower
accretion rates, increases above the critical BH mass. These observational
trends can be natural consequences of the proposed scenario of suppressing BH
growth around the apparent maximum mass of $\sim 10^{10}~M_{\odot}$. The
ongoing VLA Sky Survey in radio will allow us to estimate of the exact number
fraction of RL quasars more precisely, which gives further insights to
understand quenching processes for BH growth.
