  We present an analysis of the long-term stability of fibre-optic transmission
properties for fibre optics in astronomy. Data from six years of operation of
the AAOmega multi-object spectrograph at the Anglo-Australian Telescope is
presented. We find no evidence for significant degradation in the bulk
transmission properties of the 38 m optical fibre train. Significant losses
(<20% relative, 4% absolute) are identified and associated with the end
termination of the optical fibres in the focal plane. Improved monitoring and
maintenance can rectify the majority of this performance degradation.
