Centaurus: Surveillance Radar Approaches were part of the tool set until sometime in the late eighties (or perhaps earlier). They were intended mainly for emergency use. My memory is failing, but I think that they were available at Melbourne only for RWY 16, but I could be wrong on that. A unique SRA radar map had to be loaded, with distances and altitudes marked along the approach at frequent intervals. Before an approach could be conducted for real, the controller must have performed a practice SRA within the previous (can't remember - x) months. Very similar to GCA in performance, with higher minima because of the lack of height finding radar (we're talking Primary). Because of the requirement for constant chatter to the aircraft concerned, it had to be done on a discrete frequency, or at a very quiet time, hence your knock-back. We would get requests from pilots occasionally, which we would try to accommodate, and alternatively a controller might offer an SRA in the hope of gaining some practice, or as part of a check.