Aviation safety investigations & reports

Boeing Co 737-376 , VH-TJA

Investigation number:
Status: Completed
Investigation completed


At 0627 EST, a Boeing 737 (B737) departed Melbourne for Perth. Melbourne Sector Inner West advised Melbourne centre of the departure. An airways data systems operator (ADSO) received this information and notified Adelaide centre of the departure by intercom. He then activated the flight strips for Melbourne Sector 1 and delivered these strips to this sector. A hard copy departure message should also have been sent via the Aeronautical Fixed Telecommunications Network (AFTN) to all units affected by the flight, but this task was not completed. As a result, Perth Air Traffic Control did not receive any notification that the aircraft had departed.

For much of its flight to Perth, the B737 was on route L513 and was under the control of Melbourne Sector 1, a procedural control sector. This sector was combined with Sector 5 until approximately 0850 when it was decided to split the two sectors. The departing controller proceeded to hand over control of Sector 1 to the oncoming controller, but kept control of Sector 5.

At 0853 EST, during the Sector 1 handover/takeover, the crew of the B737 reported having passed TAPAX (a position reporting point 523 NM east of Perth) at 0852. They also reported that they were maintaining FL350, and estimating TAMOD (a position reporting point 153 NM east of Perth) at 0951. The departing controller took the position report and appropriately marked the flight strips. The report was required to be passed to the Perth Outer controller, as the sector boundary was 10 NM east of TAMOD. This coordination task was not done.

The departing Sector 1 controller later reported that he did not perform the coordination task as he assumed that the oncoming controller would do it. He also reported that he did not specifically point out the need for the oncoming controller to perform this task, but assumed that she had heard the position report and understood that it needed to be done. The oncoming controller later reported that she could not remember hearing the position report. Neither controller could recall whether the relevant flight strip had been cocked on the flight progress board to indicate that there was an outstanding task to be performed.

The oncoming controller took control of Sector 1 at 0856. Soon after taking over, Perth control contacted her to advise that an eastbound Airbus 320 (A320), VH-HYJ, was about to transfer to her frequency and that the crew would soon contact her. This crew contacted her at 0857. At 0858, immediately after taking this crew's report, the controller contacted the westbound B737's crew and advised them to contact Perth at TAMOD. This frequency-transfer task was normally performed when the aircraft was 5 minutes from TAMOD, or 0946 in this case. Shortly after performing this task, the controller removed the B737's flight strips from the flight progress board. This action was normal practice for filing the flight strips after an aircraft had left the Sector 1 area of responsibility.

At 0929 EST, another eastbound A320, VH-HYR, departed from Perth for Melbourne. The aircraft was planned on route L513 until TAMOD, before turning onto the one-way route Y53. The estimate for TAMOD was 0953. The Perth controller informed Sector 1 of the departure. He advised that the aircraft had planned FL370 but that he recommended restricting the aircraft to non-standard FL350 due to a westbound A320, VH-HYA, at non-standard FL370 and estimating TAMOD at 1006. The Sector 1 controller agreed with this restriction.

Although having the air traffic under his jurisdiction procedurally separated, the Perth Outer controller checked the radar at 0941 and observed a return approximately 220 NM east of Perth (67 NM east of TAMOD). As the displayed information was based on extreme range returns, it was considered unreliable. However, it indicated a westbound jet aircraft at FL350. The controller checked his coordinated and pending traffic, but was unable to identify the aircraft.

At 0943, Perth Outer contacted Melbourne Sector 1 to report the return and ask whether she knew its identity. The Sector 1 controller was not aware of any aircraft in that area other than HYA, the westbound A320 that was 15 minutes behind the position of the unknown aircraft. Perth suggested restricting HYR to FL330 until the problem could be rectified. Another Perth controller advised HYR's crew of the problem. At 0946, Perth Outer directed the crew to divert to the left of track, as the observed radar return's altitude was still unverified.

With the assistance of other controllers, the Sector 1 controller retrieved the used flight strips and identified the return as the B737. The relevant information was reported to Perth Outer at 0947. The aircraft was then transferred to the Perth controller.

As the A320 had been restricted to FL330 and diverted left of track, there was no breakdown in separation. The two aircraft passed each other at 0950:01. HYR passed TAMOD at 0949, and the B737 reached TAMOD at 0951. Analysis of the radar tape indicated that HYR would have reached FL350 between 0949:20 and 0950:20. The B737 was fitted with a Traffic Alert and Collision Avoidance System.

Departure Message Processing

After receiving the B737's departure notification from Melbourne Sector Inner West, the ADSO annotated the callsign, departure point, destination and departure time on an aircraft movement advice form before advising Adelaide of the departure. However, this information was not entered in the appropriate boxes on the form and the SSR code was not entered. In addition, various unnecessary items were written on the form, including the numbers of four AFTN messages that had been sent around the time that the B737's departure was being processed.

The ADSO who took the departure notification was a trainee. He was required to be directly supervised during his task performance, but this supervision was not present at the time the departure was being processed. It was later reported that workload was high at the time of the departure, and that the trainee and the supervising ADSO were both performing departure processing tasks.

Prior to the incident, the tasks required to process a departure were specified in written procedures, but they were not all specified in the same procedural documentation. The order in which the tasks should be performed was not specified in any procedural documentation.

Sector 1 Handover/Takeover

Sector 5 was in the process of being transferred from the Bight Group, which also had Sectors 1 and 4, to the Desert Group. A console for Sector 5 had been set up in the Desert Group's area, and the controllers in that group were currently being trained in Sector 5 operations. Until the transfer was completed, Sector 5 could also be operated from Sector 1's console.

Immediately after the oncoming controller took over Sector 1, the departing controller took the flight strips for Sector 5 and arranged them on the relevant flight progress board in the Desert Group. He then proceeded to conduct a training session on Sector 5 for another controller.

It is desirable for a controller to perform all outstanding tasks prior to handing over to another controller, but this is not always practical. In this case, several tasks had to be conducted during the handover/takeover and the workload level was significant. Both the departing and the oncoming controller reported that the handover of Sector 1 appeared to be well conducted. Prior to the incident, there was no written procedure that detailed all of the required tasks to be performed during a handover/takeover.

Sector Boundary

The boundary between Melbourne Sector 1 and Perth Outer was approximately 10 NM east of the reporting point TAMOD (163 NM east of Perth). The range of the relevant radar was typically 220 NM to the east of Perth between FL330 and FL370. The Perth controller was therefore able to see to approximately 50 or 60 NM east of TAMOD at high flight levels. The air route structure had been redesigned with the intention of the Perth radar being used to its full potential, but the sector boundary had not been changed.

Personnel Information

The oncoming Sector 1 controller commenced duty at 0700 on the morning of the incident. She finished duty on her previous shift at 2030 the previous night. As she lived 90 minutes from her place of work, she had only slept 5 hours during the night before the incident. Due to other factors, she had slept even less during the previous night.

In addition to not passing coordination on the B737, the oncoming controller made three minor errors during the period after she took over Sector 1 until the Perth Outer controller detected the incident. These errors were an attempt to call HYA on the wrong frequency, and two occasions of contacting the wrong Adelaide controller (as she forgot that the relevant Adelaide sectors were combined). There were no other problems noted with any aspect of her performance or behaviour during this period.

Neither of the Sector 1 controllers had received any training in the use of teamwork or team resource management skills.


Although there was no breakdown in separation, this incident involved a serious breakdown in coordination that resulted in a B737 not being under effective air traffic control from 0858 EST until after the radar return was identified at 0947. Had the Perth controller not detected the problem, there would have been a breakdown of separation. Although the two aircraft would have both been to the east of TAMOD at the time of passing, and therefore on different routes, this situation was not planned.

The incident directly resulted from a combination of active failures. The two most significant errors were: (a) the omission of a hard copy departure message via the AFTN; and (b) the omission of any coordination on the aircraft from the Melbourne Sector 1 controller.

Processing the Hard Copy Departure Message

Had the trainee ADSO sent the departure message via the AFTN, Perth control would have activated the flight progress strips and, therefore, been better prepared to detect the missing coordination on an aircraft from Melbourne Sector 1. This error consequently removed an important safety defence.

Factors that contributed to the missing AFTN message included:

  1. the aircraft movement advice form being incomplete, and therefore not providing an appropriate cue; high workload;
  2. insufficiently detailed task procedures; and
  3. a lack of direct supervision of the trainee ADSO.

It is likely that the supervising ADSO became too involved in the operation of departure processing tasks to be able to effectively monitor the trainee's performance.

Passing Coordination of the TAPAX Position Report

The omission of the oncoming Sector 1 controller to pass coordination on the B737 to the Perth outer controller meant that the Perth controller had no forewarning of the arrival of that aircraft into his airspace. Therefore, this error increased the likelihood of a breakdown of separation standards. Although the Perth controller did detect the problem in sufficient time to avoid a breakdown in separation, it is likely that such a detection would not usually occur.

Factors that contributed to the omission included the absence of clear communication between the departing Sector 1 controller and the oncoming controller as to who would pass the coordination, and the inability of the departing controller to remain available to ensure the oncoming controller was fully briefed. More specific handover/takeover procedures could have reduced the likelihood of these factors. The development of appropriate teamwork and team resource management programs would also help reduce the likelihood of such inter-controller coordination and communication failures.

The coordination omission was also partly a result of the inherent nature of the task. It was probably an action slip, or an error where the controller's actions did not proceed as planned. More specifically, the error appeared to be a substitution of one highly automatic task (asking the B737's flight crew to transfer frequency at TAMOD) for another (passing coordination on the B737 crew's TAPAX report to the Perth Outer controller). Such substitution slips are usually associated with a period of inattention or distraction. In this case, the controller may have been distracted by the call from another flight crew immediately before she performed the task. As the controller had only been working on the sector for a few minutes, she could also have been distracted by her scanning and familiarisation activities.

An increase in the likelihood of skill-based errors is often correlated with fatigue. In this case, the controller had a less than normal amount of sleep in the 2 nights prior to the incident. However, the investigation was unable to determine if fatigue influenced the controller's performance at the time of the occurrence.

There were cues available to alert the Sector 1 controller to the error, such as the times on the TAMOD strip and the absence of a tick in the last box of the TAPAX strip. However, having developed the intention to conduct a frequency-transfer task, it is unlikely that the controller would have considered checking times on a strip. In addition, research has shown that the absence of a cue (such as a tick) is often not detected. Shortly after the error occurred, the controller disposed of the flight strips and effectively removed any remaining cues she could use to detect the error.

With the introduction of The Australian Advanced Air Traffic System (TAAATS) throughout Australia in 1998 and 1999, the likelihood of this specific type of error should be reduced. Transfers of aircraft between sectors will be conducted automatically. In addition, for procedural control sectors such as Sector 1, the spatial positions of aircraft will be pictorially displayed. It is reasonable to expect that these changes will reduce the likelihood of a controller incorrectly perceiving the position of an aircraft.

Flight Levels

The westbound A320, VH-HYA, was maintaining a non-standard flight level (FL370) which resulted in an eastbound A320, VH-HYR, being given a non-standard level (FL350) for the initial level clearance. This consequential action had the effect of placing VH-HYR in direct conflict with the B737. Had standard levels been applied on the two-way route system that was under procedural control, a safety net would have been put in place. This net would have become prominent had the Perth controller not observed the radar paint of the B737.

Significant Factors

  1. The ADSO did not send a hard copy departure message on the B737's flight.
  2. The ADSO was a trainee and was not adequately supervised.
  3. The Sector 1 handover/takeover involved poor inter-controller communication and coordination.
  4. The oncoming Sector 1 controller did not pass coordination of the B737's TAMOD position report to the Perth Outer controller.
  5. There was a lack of appropriate procedures in relation to the departure processing task and the handover/takeover task.

Safety Action

As a result of this and other incidents, the Bureau of Air Safety Investigation (BASI) examined issues associated with Airservices Australia's operation of teams in air traffic services. This examination resulted in BASI issuing the following Safety Advisory Notice to Airservices Australia on 27 January 1998:

Safety Advisory Notice SAN 970137

Airservices Australia should note the safety deficiencies detailed in this document and take appropriate action.

The safety deficiencies referred to in this document were:

  1. an undesirably low level of operational support provided by experienced controllers, including team leaders and other full performance controllers, to controllers working in operational positions.
  2. an inappropriately low level of emphasis on team development activities, such as the provision of team leader training and support, and the regular provision of team days with structured learning content for team members.
  3. performance evaluation systems for team leaders that do not ensure relevant team leader performance areas are measured, and also do not ensure that any degradation in a team leader's proficiency on operational positions will be detected.
  4. an inappropriately low level of training and development for many controllers on human factors issues, particularly those associated with inter-controller coordination and communication.

Following receipt of this safety action notice, Airservices Australia instigated an independent review of operational supervision issues in their air traffic services' activities. This review was completed on 15 October 1998. In addition, an introductory training package for team resource management has been developed and a pilot course has been conducted.

As a result of this and other occurrences, BASI is also investigating perceived safety deficiencies associated with the design of air traffic controller shift schedules, and the allocation of a controller's tasks within a shift. Any recommendation arising from these investigations will be published in BASI's Quarterly Safety Deficiency Report.

Local Safety Action

Local safety action proposed by Melbourne Enroute as a result of this and other incidents includes the production of a local instruction defining the procedures and responsibilities involved in handover/takeover situations. This procedure is currently being trialled in the Bight Group. A specific procedure has also been developed for the ADS0s outlining the steps required to process departure messages, and the required order of these steps.

Melbourne Enroute and Perth Area are currently assessing the suitability of Perth taking over responsibility for that part of Melbourne Sector 1 that is covered by Perth radar. This approach is consistent with BASI Interim Recommendation 970112 to Airservices Australia for radar to be used for air traffic control where radar coverage is available.

General details
Date: 28 August 1997   Investigation status: Completed  
Time: 0945 hours EST    
Location   (show map): 37 km ESE TAMOD, (IFR)    
State: Western Australia   Occurrence type: Breakdown of co-ordination  
Release date: 01 February 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-TJA  
Serial number 24295  
Type of operation Air Transport High Capacity  
Damage to aircraft Nil  
Departure point Melbourne, VIC  
Departure time 0627 hours EST  
Destination Perth, WA  

Aircraft 2 details

Aircraft 2 details
Aircraft manufacturer Airbus Industrie  
Aircraft model A320  
Aircraft registration VH-HYR  
Serial number 622  
Type of operation Air Transport High Capacity  
Damage to aircraft Nil  
Departure point Perth, WA  
Departure time 0929 hours EST  
Destination Melbourne, VIC  
Last update 13 May 2014