Aviation safety investigations & reports

Boeing Co 737-376, VH-TAG

Investigation number:
Status: Completed
Investigation completed


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.


This scenario only occurred prior to first light, which occurred after 0600 from approximately the end of March until early September. The problem with the SIDs converging during daylight hours was normally overcome by the cancelling of the SID and the issuing of a radar departure instruction while the aircraft is on the ground prior to departing RWY 03, thus providing separation assurance.

Prior to first light, separation assurance could have been achieved by DEP applying vertical separation between aircraft departing these runways, or by exercising control over aircraft release times to ensure that a radar standard would exist between them.

The DEP controller did not ensure separation between the B737 and the preceding BAe146 by permitting the trainee to issue an instruction of "unrestricted" to the ADC.

The crew of the BAe146 provided a prompt to the controller by requesting a clearance direct to Ballidu shortly before commencing a turn off runway heading. However the crew were advised by the DEP trainee that the request was understood and that he "will advise".

A second prompt occurred to the training officer when the crew of the B737 called on the DEP frequency reporting that they were leaving 1,800ft. It appears that this prompt alerted the training officer to the developing situation, as he then instructed the trainee to turn the BAe146.

The training officer at this point still did not intervene directly, but instead indicated to the trainee that he needed to give the crew of the BAe146 a heading in order to resolve the situation more quickly. The provision of traffic information or use of "immediate" may have been appropriate under the circumstances.

That the training officer did not intervene until after the incident had largely been resolved was indicative of inattention to the operational situation and a lack of understanding of the criticality of the situation. The training officer displayed a lack of control over the trainee at a time when the issue of precise instructions and a need to alert the crew of the situation was critical. Instructions issued to the trainee were in general terms rather than the specific terminology that the situation demanded.

The task of the ADC in this instance was to manage the runway departures in accordance with instructions from the DEP controller. The ADC and ADC trainee, both understood that the primary responsibility for separation for aircraft on the 03 and RWY 06 PEPPA3 SID, lay with the DEP controller.

The ADC advised that he continued to visually monitor both aircraft via their departure tracks, even though responsibility for separation lay with the DEP controller. He also advised that at no stage did he offer to take, or accept any, responsibility from the DEP controller for separation of the aircraft.

When asked by the DEP controller whether he could monitor, the response of "Yes, I'm monitoring" was intended to indicate that he had the aircraft in sight and that, at that time, by visual observation their tracks had begun to diverge. He was thus indicating that he was able to monitor that the aircraft tracks were not likely to come together, but was not indicating any acceptance of responsibility for separation.

The training configuration utilised by the ADC and DEP was such that the trainers were unable to directly override their trainees. Use of available override systems would have made it easier for the trainers to readily communicate with the crews.

Safety Action

As a result of this incident, Airservices Australia recommended that:

  1. Team leaders brief controllers on the necessity to provide separation assurance where that assurance is not provided on system routes.
  2. Override facilities are to be used.

A cross familiarisation program between the tower and terminal control staff was developed and an education program was devised to ensure both areas have a better understanding of standard system routes.

The Manual of Air Traffic Services (MATS) has been amended to allow controllers to cancel a SID during hours of darkness and instruct crews to depart on runway track using the climb gradient specified in the cancelled SID.

General details
Date: 06 May 1999   Investigation status: Completed  
Time: 0605 hours WST    
Location   (show map): 9 km ENE Perth, (VOR)    
State: Western Australia   Occurrence type: Loss of separation  
Release date: 05 September 2001   Occurrence category: Incident  
Report status: Final   Highest injury level: None  

Aircraft 1 details

Aircraft 1 details
Aircraft manufacturer The Boeing Company  
Aircraft model 737  
Aircraft registration VH-TAG  
Serial number 23478  
Type of operation Air Transport High Capacity  
Damage to aircraft Nil  
Departure point Perth, WA  
Destination Adelaide, SA  

Aircraft 2 details

Aircraft 2 details
Aircraft manufacturer British Aerospace PLC  
Aircraft model BAe 146  
Aircraft registration VH-JJP  
Serial number E2037  
Type of operation Air Transport High Capacity  
Damage to aircraft Nil  
Departure point Perth, WA  
Destination Broome, WA  
Last update 13 May 2014