Socata TB10, VH-XYF

A Tobago TB10 had departed Townsville on a night visual flight rules flight which was on a track to the west of the airport. The lowest safe altitude for the track was 5,200 ft and the pilot had been approved by the approach controller to set course from overhead the airport. Additionally, the approach controller had required the pilot to remain east of the airport but over land, in order to provide separation from other air traffic.

A BAe146 had taxied for a flight to Brisbane and the crew was cleared for take-off on a runway 01 JEMMA 1 standard instrument departure. That departure track involved a right turn after take-off to a heading of 070 degrees with subsequent turns taking the aircraft to the south-east of the airport.

The approach controller cancelled the requirement for the Tobago to remain east of the airport as the conflicting traffic had passed the conflict area. However, in cancelling the requirement, the controller did not specifically instruct the Tobago pilot to track on a westerly heading. The pilot remained over land, and east of the airport, while continuing climb.

The BAe146 had departed and was in a right turn but the crew had delayed transferring radio frequency to the approach controller in order to report a bushfire that was burning north of the airport to the aerodrome controller. During that time, the Tobago pilot had commenced a right turn towards the north-east. Those actions resulted in the aircraft being on conflicting headings without instructions or amended clearances that would ensure the vertical separation standard of 1,000 ft would be maintained.

The approach controller instructed the Tobago pilot to "take up a westerly heading" but that instruction was not acknowledged. As the BAe146 crew had not transferred to the departure radio frequency, the controller instructed the Tobago pilot to turn to the south in an attempt to maintain the 3 NM radar separation standard as the there was less than 1,000 ft between the aircraft's altitudes. The Tobago pilot acknowledged the instruction and, at about the same time, the BAe146 crew transmitted on the departure frequency. The approach controller then instructed the BAe146 crew to turn left onto a heading of 090 degrees for avoiding action. At that point, the Tobago was 3 NM away and on a closing heading.

Both crews carried out the instructions and radar analysis indicated that the lateral and vertical distance between the aircraft were 1.8 NM and 500 ft respectively. There had been an infringement of separation standards that required 3 NM lateral or 1000 ft vertical separation.

Townsville Air Traffic Control was operated by the Royal Australian Air Force. An investigation by the Directorate of Flying Safety - Australian Defence Force revealed that the approach controller had expected the Tobago pilot to take up a westerly heading as soon as the requirement to remain east of the aerodrome was cancelled. The approach controller also expected that the tracks of the aircraft would remain more than 3 NM apart. The unexpected actions of the Tobago pilot meant that the expectations of the controller were not met and, when combined with the later than normal radio transfer by the crew of the BAe146, left the controller with few options to remedy the situation in a timely manner.

The lack of the use of separation assurance techniques placed the aircraft in a conflict situation.