The aircraft was on charter to Australian Airlines operating as Flight Number AUS656. The aircraft was inbound to Sydney via the 07 Localiser. Approaching 7000 feet, on first contact with Sydney Approach South, the aircraft was instructed to descend to 4000 feet, not below the DME (Distance Measuring Equipment) steps. The DME Arrival Procedure indicates the aircraft should not descend below 5000 feet until 19 DME, to maintain separation from uncontrolled traffic below the DME steps. At 22 DME, the aircraft's altitude readout (on the Sydney Approach Radar) indicated, and was confirmed as, 4100 feet. There was no known traffic confliction. The DME Arrival Procedure for Sydney is not in accordance with ICAO Doc 8168- Ops/611 and may not be used by international operators. However, the aircraft was operating on a domestic flight plan, and only the three letter call sign and domestic flight number were on the flight progress strip held by the Sydney Approach Controller. Since this incident, the Civil Aviation Authority have issued an instruction that DME Arrival Procedures, which are not in accordance with ICAO standards, will not be issued as clearances to any aircraft, domestic or international.
