Operational non-compliance involving a Piper Aircraft Corp PA-31-350, VH-WAD, 25km N Sydney, NSW on 26 February 1993

The aircraft was issued with a take-off clearance, with a requirement to maintain 3000 feet. On departure, the pilot reported on climb to 3000 feet. The aircraft was then observed on radar to be approaching 3800 feet. When queried, the pilot confirmed his altitude was 3800 feet. The aircraft was then cleared to maintain 4000 feet to ensure separation with crossing traffic arriving at Sydney. The pilot later stated that he understood his initial clearance limit to be 4000 feet.