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An infringement of the 3NM radar separation standard occurred at 0606 western standard time approximately 5NM to the northeast of Perth. The aircraft involved were a British Aerospace 146 (BAe146) that departed Perth on a RWY 03 BIU2 standard instrument departure (SID) followed shortly after by a Boeing 737 (B737) that departed on a RWY 06 PEPPA3 SID.

The 03 BIU2 SID is designed to provide system separation with military airspace to the north of Perth and, as a consequence joins the 06 PEPPA3 SID at position REDIL, 8NM to the northeast of Perth. Military airspace was not active at the time of the incident.

The aircraft were under the control of the Perth Departures (DEP) controller at the time. The responsibility for the provision of separation of aircraft on these two SIDs was defined in Perth Local Instructions as the responsibility of the DEP controller.

The DEP controller was monitoring a trainee controller on DEP who was approaching the final stages of rating training. The controller did not use an "override" box that would have allowed him to override the trainee and transmit instructions to the crews.

The aerodrome controller (ADC) advised the trainee DEP controller that the B737 was next for take off. The trainee DEP controller issued the ADC an unrestricted clearance for the B737 to depart.

The crew of the BAe146 heard the B737 being cleared for takeoff and realised that the two aircraft were on conflicting departure routes. The crew asked the trainee DEP controller for a clearance direct to Ballidu in an attempt to resolve the situation. The controller advised the crew that he "would advise" when the direct clearance was available.

The B737 departed and the crew contacted DEP control and advised that they were leaving 1,800 ft. The crew of the BAe146 monitored the proximity of the B737 visually and on the Traffic Alert and Collision Avoidance System (TCAS). The TCAS equipment did not provide a traffic or resolution advice.

The DEP controller did not intervene directly and prompted the trainee to turn the BAe146 away from the B737. The trainee then issued an instruction to the crew of the Bae146 to cancel the SID and track direct to Ballidu. The DEP controller then instructed the trainee to give the crew of the BAe146 a heading in order to resolve the situation. The trainee responded by instructing the crew of the BAe146 to turn left heading 360 degrees for separation. The trainee then instructed the crew of the B737 to turn right heading 090 degrees for separation.

Traffic information was not passed to either crew, nor was the word "immediate" used in passing heading instructions. There was no relay of the urgency of the situation to either crew by phraseologies used by the trainee. At that time the training officer utilised the APP console handset to contact the ADC on the hotline. The ADC was asked by the DEP controller "can you just monitor", to which the response from the ADC was "Yes I'm monitoring". The DEP controller later reported that in his mind it was a request for the ADC to provide visual separation between the aircraft. He also reported that the response received from the ADC indicated to him that the ADC had been providing separation throughout the event by visual monitoring of the aircraft.

The ADC was monitoring a trainee controller by use of a headset. The "B", or training system handset, was not being utilised. The ADC was unable to override the trainee without actually taking over the ADC handset from the trainee.

The DEP controller was not aware of the training on the ADC position and the ADC controller was not aware of the training on the DEP position.

Recorded radar data indicated that separation reduced to 1.4NM with a vertical separation of 200ft. The aircraft were separated by 1.5NM while at the same level. Minimum required radar separation for these aircraft while not 1,000ft vertically separated was 3NM.

The procedures in use were the standard procedures applicable for the use of runways 03/06 for departing aircraft prior to first light. These procedures required the issue of departure instructions for aircraft departing at night or in IMC to be in the form of a SID. It was not permissible for a controller to cancel a SID and issue a radar departure instruction while the aircraft is on the ground prior to first light. It was only permissible in these circumstances to cancel the SID after the aircraft was airborne and had reached the Minimum Vectoring Altitude (MVA). In the case of the 03 BIU2 SID, this situation provided a very short window of opportunity between the aircraft reaching the MVA and commencing a right turn off runway heading. Reliance on controller intervention to cancel this SID and issue a maintain runway heading instruction in order to maintain separation with SID departures from RWY 06 provided no separation assurance.

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