  Using the operator approach, we obtain quasinormal modes (QNMs) of BTZ black
hole in spin-3 topologically massive gravity by solving the first-order
equation of motion with the transverse-traceless condition. We find that these
are different from those obtained when solving the second-order differential
equation for the third-rank tensor of spin-3 field subject to suitable boundary
conditions and having the sign ambiguity of mass. However, it is shown clearly
that two approaches to the left-moving QNMs are identical, while the
right-moving QNMs of solving the second-order equation are given by descendants
of the operator approach.
