A Grumman G-73 Mallard amphibian was destroyed when it impacted the water of Swan River in Perth, Australia. The pilot and his passenger suffered fatal injuries. The aircraft was flying a display during the City of Perth Australia Day Skyworks 2017 event. It departed Serpentine Airport at 16:28 and proceeded along the coast towards Perth. A holding pattern was flown to the east of Garden Island at an altitude of approximately 1600 feet, waiting to fly a display. At 16:50 it continued flying north towards Perth in company with a Cessna Caravan amphibian. Both aircraft conducted a series of circuits that included low-level fly-pasts of the Langley Park foreshore. After the second fly-past, the pilot of VH-CQA commenced a third circuit, while the Caravan departed the area. As part of the third circuit, the pilot of the Mallard flew in an easterly direction, parallel with the South Perth foreshore, before commencing a left turn. This would have facilitated a third pass in a westerly direction along the Langley Park foreshore. During the left turn, the aircraft rolled left and pitched nose down, consistent with an aerodynamic stall. The aircraft collided with the water and broke up. The pilot and passenger were fatally injured. Contributing factors: – The pilot returned the aircraft to the display area for a third pass in a manner contrary to the approved inbound procedure and which required the use of increased manoeuvring within a confined area to establish the aircraft on the display path. – During the final positioning turn for the third pass, the aircraft aerodynamically stalled at an unrecoverable height. – The pilot’s decision to carry a passenger on a flight during the air display was contrary to the Instrument of Approval issued by the Civil Aviation Safety Authority for this air display and increased the severity of the accident consequence.