  During the period 1966.5 - 2006.2 the 15GHz and 8GHz lightcurves of 3C454.3
(z=0.859) show a qsasi-periodicity of ~12.8 yr (~6.9 yr in the rest frame of
the source) with a double-bump structure. This periodic behaviour is
interpreted in terms of a rotating double-jet model in which the two jets are
created from the black holes in a binary system and rotate with the period of
the orbital motion. The periodic variations in the radio fluxes of 3C454.3 are
suggested to be mainly due to the lighthouse effects (or the variation in
Doppler boosting) of the precessing jets which are caused by the orbital
motion. In addition, variations in the mass-flow rates accreting onto the black
holes may be also involved.
