VH-LRT was on a visual flight rules (VFR) flight from Riddell via Albury to Bankstown and cruising at 7500 feet. The pilot was having difficulty with visual navigation due to cloud cover and as a result the aircraft entered the Wagga control area steps without an airways clearance. VH-CMH was on climb out of Wagga for Sydney when the crew saw LRT on a converging heading and estimated it was 500 ft to 700 ft below. The crew of CMH reported that there was scattered to broken cloud from 1500 ft to flight levels. They reported the intruding aircraft to Wagga tower. The tower controller in turn checked with the Melbourne sector eight radar controller who advised there was an unidentified aircraft painting at 7500 ft 25 miles to the northeast of Wagga. That aircraft was duly identified as LRT, the offending aircraft. LRT had previously transgressed twice on the trip from Riddell, on one occasion entering controlled airspace, climbing through 10,000 ft without a clearance and on the second occasion leaving a cleared altitude without a clearance while transitting Albury control area steps. For this reason the Melbourne sector eight radar controller had been monitoring the aircraft's progress but had lost radar contact when the aircraft was to the south of Holbrook. The radar tape was monitored and revealed that a code 2000 return appeared on radar about 16 minutes later at a position 15 miles south of Wagga at 8400 ft on a northerly track entering Wagga CTA. It was later determined that this return was LRT. The tape showed that LRT proceeded in a north-north-easterly direction through Wagga CTA and gradually descended to 7000 feet when, at 15 miles northeast of Wagga, the two aircraft were one mile apart at the same altitude. Factors The following factors were considered relevant to the development of the incident: . The pilot of LRT was not competent to navigate his aircraft in the cloud conditions existing at the time. This resulted in the aircraft entering the Wagga CTA without a clearance and because the Wagga air traffic controllers were unaware of LRT, they had not arranged separation with CMH. . The Melbourne sector eight controller had been watching LRT, because of earlier incursions, until its return disappeared from radar. Although Wagga airspace is not the responsibility of the Melbourne sector eight controller, it is considered that in this instance when the code 2000 return appeared entering Wagga airspace, the sector eight controller should have suspected that it may be LRT and alerted the Wagga controllers accordingly. Such an alert should have resulted in this incident being avoided.