  We consider a 9-PDE (1-space and 1-time) model of plane Couette flow in which
the degrees of freedom are severely restricted in the streamwise and
cross-stream directions to study spanwise localisation in detail. Of the many
steady Eckhaus (spanwise modulational) instabilities identified of global
steady states, none lead to a localized state. Localized periodic solutions
were found instead which arise in saddle node bifurcations in the Reynolds
number. These solutions appear global (domain filling) in narrow (small
spanwise) domains yet can be smoothly continued out to fully spanwise-localised
states in very wide domains. This smooth localisation behaviour, which has also
been seen in fully-resolved duct flow (Okino 2011), indicates that an
apparently global flow structure needn't have to suffer a modulational
instability to localize in wide domains.
