At 1550 VH-RUH, enroute Broken Hill to Moorabbin, reported overhead Natya at 7,000 ft. At 1552 VH-LJR, enroute White Cliffs to Essendon, reported overhead Natya, also at 7,000 ft. The Flight Service (FS) 14 operator was expecting LJR to be at its planned level of 5,000 ft. Neither aircraft was aware of the other and traffic information was immediately passed. Investigation revealed that the pilot of LJR requested traffic for a climb to 7000 ft 16 minutes after departure from White Cliffs. That request was to the FS15 operator. Nine minutes after that request the pilot of LJR reported maintaining 7,000 ft. Departure co-ordination from FS15 to FS14 was done manually because the operators were too busy on their frequencies to do it by intercom.
The investigation was unable to determine whether the level change was co-ordinated as part of the departure co-ordination. The pilot of LJR called FS14 at 1510 (42 minutes before he reported over Natya) and reported maintaining 7,000 ft and an amended estimate for Natya. The FS14 operator did not realise that LJR was no longer at its planned level and the FS14 flight strip still indicated 5,000 ft. When the aircraft later reported at Natya, there was a different operator working the FS14 position. He immediately noticed the aircraft was not at its planned level of 5,000 ft which was still annotated on the flight strip. Both FS15 and FS14 were very busy at the time. FS15 was dual manned and in addition to normal traffic was handling a difficult distress phase which extended over a protracted period.