Capt Fathom
I was a controller in Sydney during the '70's, and from what I remember, when the Sandringham's stopped flying from Rose Bay to Lord Howe, then Beech 200 Super King-air's took over (Advance Airlines), and when QANTAS DC-4's stopped flying on the Sydney to Norfolk run, not long after, then East West airlines started operating that route with F-27's. We (Sydney Ground) used to give the airways clearance to the flying boats when they were taxying (?) and co-ordinate with the DCA launches that supervised the departure path. A typical clearance to the flying boats was "Remain not above 500', remain East of the Harbour Bridge, and call Departures on ----- airborne". As often as not the Sandringham's would continue to Lord Howe at either 500' or a Thousand.
I still have sharply imprinted in my mind the sight of one of the Sandringham's thundering across the harbour from Rose Bay at about 6 one summer morning when I was out fishing with some mates, and it passed about 100 metres from us, bellowing like hell, struggling to get on to the step.