Aviation safety investigations & reports

Boeing Co 737-33A, VH-CZU

Investigation number:
Status: Completed
Investigation completed


A Boeing 737 (B737) departed runway 34R on an ENTRA ONE standard instrument departure (SID), on climb to 5,000 ft. Immediately after departure, the crew established communication with the Departures North (DN) controller.

A Metro, inbound to Sydney from the north, was being radar vectored for a wide downwind leg to runway 34R, maintaining 7,000 ft, having earlier been diverted to the east for sequencing with preceding slower traffic. Although this track placed the aircraft in DN airspace, the Metro crew, as instructed, remained in communication with the Approach North (AN) controller. On request, the AN controller had been granted approval by the DN controller for the Metro to transit through the DN controller's airspace. The weather conditions were fine, and runway 34 parallel operations had been in progress for 18 minutes.

The DN controller had elected to provide vertical separation between the two aircraft by issuing instructions that would enable the B737 to climb above the Metro. This plan was coordinated with the AN controller. A clearance to climb to flight level 280 was issued to the crew of the B737, with a request to expedite climb through 8,000 ft. As this transmission was being made by the DN controller, the AN controller instructed the crew of the Metro to turn right onto a heading of 170 degrees for the downwind leg.

Subsequently, it was perceived by the DN controller that the effective climb performance of the B737 would be insufficient to ensure that the required separation standard of 1,000 ft vertically or 3 NM horizontally between the two aircraft would be maintained. The controller amended the clearance and instructed the crew of the B737 to maintain 6,000 ft. However, because the B737 was climbing at 4,500 ft/min, it had climbed to 7,000 ft before the crew were able to stop the climb and commence descent. As there was now less than 3 NM between the aircraft, both controllers passed traffic information to the crew of their respective aircraft. The crew of the B737 sighted the Metro, passing beneath that aircraft with approximately 600 ft of vertical separation. The crew of the Metro did not sight the B737.

During the two years since the AN controller had been rated, the system in which he was working had changed significantly due to noise-sharing arrangements at Sydney (Kingsford-Smith) Airport. The controller's training and endorsement had been undertaken and achieved in a less complex environment. The unpredictability of the more complex arrangements required a high degree of coordination for which the controller had not been adequately trained.

Conversely, the DN controller had gained his initial rating in the days when air traffic control was more reactive and dynamic than the present more regulated system. In the previous, less structured air traffic control environment that the controller had been trained in, there had been undocumented procedures that everyone was aware of. Those procedures were passed on from controller to controller as skills were developed and refined. The DN controller expected that his intentions and plan would be readily interpreted by the AN controller.


The investigation revealed that each controller had different expectations of the intentions of the other. The DN controller had expected the AN controller's Metro would continue on its current track, and that the two aircraft tracks would cross. Conversely, the AN controller expected to keep his aircraft inside the track of the departing B737. Neither the coordination nor communication between controllers was effective. The unexpected turn onto downwind by the Metro, towards the B737, reduced the distance available for the B737 to climb safely above the Metro. The DN controller attempted to stop the B737 at 6,000 ft, but that instruction, combined with the rate of climb of the aircraft, was unable to prevent a breakdown of the vertical separation standard.

Significant Factors

  1. Appropriate separation assurance techniques were not implemented by either controller.
  2. Coordination between controllers was ineffective.

Safety Action

As a result of this investigation, and a number of similar occurrences, the Bureau of Air Safety Investigation undertook a systemic investigation into factors underlying air safety occurrences in Sydney Terminal Area airspace and issued report B98/90 on 18 August 1998. Nine recommendations were made in the report; the following three were considered relevant to this investigation.

"The Bureau of Air Safety Investigation recommends that Airservices Australia review the application of the "teams" concept within the Sydney Terminal Control Unit to ensure that teams are resourced appropriately and that there is an ongoing commitment to the provision of adequate training in order to achieve a high level of controller proficiency and standardisation."

"The Bureau of Air Safety Investigation recommends that Airservices Australia ensure that adequate refresher training is undertaken by controllers in order to provide for high levels of controller proficiency and standardisation so that the integrity of safety cases, in which refresher training is deemed to be a mitigating strategy for identified hazards, is maintained."

"The Bureau of Air Safety Investigation recommends that Airservices Australia reassess the human factor hazard analysis for both Stage One and Stage Two of the Long Term Operating Plan safety cases, so that the mitigating strategies applied to identified hazards adequately allow for the fundamental limitations of human performance. In reassessing this hazard analysis, BASI recommends that Airservices Australia seek the assistance of human performance expertise".

The following responses were received from Airservices Australia on 16 November 1998:

"A recent review of Sydney ATS has resulted in a "spill" of all management positions and a subsequent recruitment program which will be completed by 16 November 1998 to coincide with the Airservices' Business Transformation program.

The first step in this review has been to ensure that the management structure of the facility can operate effectively and that appropriate skills are available within the team. The manner in which the teams operate is the subject of a concurrent review process.

In support of these reviews, a consultant has completed a wide ranging review of supervision within air traffic services and its application within Teams.

Recommendations from these studies will be introduced into the Sydney rostering committee deliberations examining a better framework for TCU rosters. Sydney ATS management plan to introduce a revised roster in the TCU by 1 February 1999.

Team Leader training is recognised as vital to the success of teams and during October and November all Team Leaders will complete a series of Human Factors and Team Resource training modules. To further ensure that Team Leaders are better equipped to perform their duties a specific training programme for each Team Leader will be developed by 22 December 1998".

Response classification: CLOSED - ACCEPTED

[R980158] "Airservices provides familiarisation training in various forms before the introduction of new procedures and to maintain controller skill levels. This ongoing programme has been augmented by an additional period of refresher training which all TCU controllers will undertake during the remainder of this year".

Response classification: CLOSED - PARTIALLY ACCEPTED

"The LTOP Stage One and Stage Two Safety Cases have been subject to review by independent experts in the field as well as being the subject of a number of post implementation reviews. Recommendations arising from those reviews have been progressively evaluated and applied as appropriate.

Airservices will consider augmenting its review processes with human factors expertise in future".

Response classification: OPEN

General details
Date: 29 May 1998   Investigation status: Completed  
Time: 0708 hours EST    
Location   (show map): 22 km NE Sydney, Aero.    
State: New South Wales   Occurrence type: Loss of separation  
Release date: 16 September 1999   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-CZU  
Serial number 27267  
Type of operation Air Transport High Capacity  
Damage to aircraft Nil  
Departure point Sydney, NSW  
Departure time 0708 hours EST  
Destination Coolangatta, QLD  

Aircraft 2 details

Aircraft 2 details
Aircraft manufacturer Fairchild Industries Inc  
Aircraft model SA227  
Aircraft registration VH-NEK  
Serial number AC-615B  
Type of operation Air Transport Low Capacity  
Damage to aircraft Nil  
Departure point Tamworth, NSW  
Destination Sydney, NSW  
Last update 13 May 2014