Piper Cheyenne 111 aircraft VH-NMA was on a charter flight from Mangalore Vic. to Point Cook Vic. via Fentons Hill and Melbourne. The weather was clear with unlimited visibility. The flight was conducted under Instrument Flight Rules, cruising at 10,000ft. The normal crew compliment for this aircraft is 1 pilot, however for this flight, the charterer had specified that the crew shall consist of 2 pilots. Approaching top of descent the crew selected and identified the Point Cook NDB and also entered the coordinates into the GPS. Descent to 9,000ft was commenced overhead Fentons Hill which left 27 track miles to run to Point Cook. The intention was to join a right downwind pattern for a landing on runway 35. Clearance for further descent to 5,000ft was received after a change of frequency from centre to approach. At this stage an airfield was very close and the co-pilot pointed it out to the pilot-in-command who agreed it was Point Cook. The pilot-in-command then became engrossed in descending from 5,000ft as the airfield was by then almost under the aircraft. The crew did not refer to the on-board navigation equipment to confirm the aerodrome was Point Cook, nor did they refer to any topographical information. In fact they were descending over Laverton airfield. After cancelling SAR with Melbourne the crew joined the circuit and landed at Laverton which is 5 nm north of Point Cook. Laverton airfield is a decommissioned RAAF base with a similar runway configuration to Point Cook. Although decommissioned, there were 7 windsocks still in place, only one of which was marked with a cross to indicate that the airfield was closed. However, crosses had been placed on the runways to signify that they were not to be used. The crew had seen and discussed the crosses as they were approaching to land: they mistook them as displaced threshold markers and commented that the NOTAMS did not mention a displaced threshold at Point Cook. Laverton is surrounded by major road, rail and suburban infrastructure while Point Cook is immediately adjacent to Port Philip Bay with substantial open farm land nearby. The crew agreed that the misidentification occurred because of many factors some of which included: - a late descent clearance, - pre-occupation with loosing altitude - lack of attention to topographical details - lack of attention to available navigation aids - reliance of runway layout and orientation as the sole means of identification, - lack of situational awareness about the reason for the crosses on the runway ,and - changing from instrument flight rules to visual flight rules without ensuring that relevant navigation processes were co-ordinated. The operator has required all crews: - to review charts and have an appreciation of the major topographical features of all destination airfields. - to review the relevant airfield features during approach briefing, and - continually review all previously identified navigation aids, even in VMC to ensure correct identification of airfields. The RAAF has ensured that all relevant airport facilities at Laverton adequately show that the airfield is decommissioned.