  It has been reported that a fully localized turbulent band in channel flow
becomes sustained when the Reynolds number is above a threshold. Here we show
evidences that turbulent bands are of a transient nature instead. When the band
length is controlled to be fixed, lifetimes of turbulent bands appear to be
stochastic and exponentially distributed, a sign of a memoryless transient
nature. Besides increasing with the Reynolds number, the mean lifetime also
strongly increases with the band length. Given that the band length always
changes over time in real channel flow, this size dependence may translate into
a time dependence, which needs to be taken into account when clarifying the
relationship between channel flow transition and the directed percolation
universality class.
