A Boeing 767 (B767) was en route from Sydney to Jakarta, Indonesia, on the two-way air route A576 and was estimating overhead Alice Springs at 1255 Central Standard Time at flight level (FL) 280. The crew of an Airbus Industrie A320 (A320) taxiing at Alice Springs had also flight planned via A576, in the opposite direction to the B767, for Sydney. The A320 crew had planned the flight at FL370 but the Alice Springs sector controller, operating from the Melbourne air traffic control centre, intended to issue a clearance of FL270 to the crew. This would have provided the required 1,000 ft vertical separation standard between the A320 and the B767. The A320 departed at 1218 on climb initially to FL200 and the crew contacted the controller at 1225. The controller entered FL270 in the air traffic system but told the crew to climb to FL280. The crew correctly read back FL280.
The estimated time of passing of the two aircraft was 1237. The controller told both crews the opposite direction aircraft was 1,000 ft above or below them respectively and to report sighting the other aircraft. At 1236 the A320 crew reported to the controller that they were descending because of a traffic alert and collision avoidance system resolution advisory. The controller acknowledged the report and then queried the B767 crew about the traffic alert and collision avoidance system event. The B767 crew confirmed that their aircraft's systems had received a traffic alert and collision avoidance system resolution advisory to climb.
Later analysis of aircraft data showed that both aircraft had been maintaining FL280 on reciprocal tracks. The combined closing groundspeed of the aircraft was 920 kts and they were about 9 NM apart when the traffic alert and collision avoidance system activated. As the crews complied with the resolution advisory the A320 crew saw the B767 pass above them when the vertical spacing and lateral distance between the aircraft was 900 ft and 0.5 NM respectively. There was an infringement of separation standards.
Controller background
The controller had over 10 years experience in en route and five years in tower control. Following a staff rationalisation exercise the controller reluctantly moved from Moorabbin to the Melbourne centre in mid-1998. Since that time, he had experienced increasing levels of stress because of:
- dissatisfaction with career opportunities,
- problems with undertaking night duty,
- personal problems with supervisory staff,
- unsuccessful applications for positions in the tower, and
- a recent diagnosis of the critical illness of a family member.
For example, on the day before the occurrence the controller was told that he had again been unsuccessful in a recent selection exercise for positions in the tower or terminal area streams. This was a source of stress to the controller.
Day of the occurrence
The controller reported that he did not have breakfast because of the early start and woke at 0400 after about 5 hours sleep. He began work at 0530. He later said he felt "somewhat tired" on the day of the incident and that he did not feel his limited period of sleep influenced his performance. Individuals suffering mild to moderate fatigue are generally unaware of decreasing levels of performance.
This was to be the controller's last working shift before starting leave. The controller had been approved to take 2 weeks leave to be able to be with his family because of the illness of the family member.
About 3 hours before the occurrence the controller was relieved at the position to enable him to meet with the centre manager. The centre manager advised that a claim of harassment by the controller had been investigated and was dismissed. This information distressed the controller. The centre manager told him to take time to compose himself before going back to the console or operations room. During this exchange the controller advised the centre manager of the strain he was under because of the recent diagnosis of a family member with a terminal illness. Before this meeting the centre manager was unaware of the illness in the controller's family. The centre manager told him that he didn't have to return to the console - it was his choice.
Airservices' Australia (Airservices) Civil ATS Operations Administration Manual (CATSOAM) provides guidance material on stress awareness for Airservices' staff. It states in part that "routine tasks with monotonous or minimum workload can cause some people to run over previous events or issues and, if they have been unpleasant or difficult, then concentration on the task being performed may deteriorate". It also warns that "stress is cumulative and can affect performance at work" and includes a caution that "professional guidance should be sought in case of doubts concerning mental state and fitness for work". With illness, injury or medication the manual places the onus on individuals to ensure that they are able to undertake rostered duties. It states, "a person having any doubt about their fitness to perform at the correct level for a full tour of duty must tell the appropriate supervisor. They should be stood down from operational duties until they feel fit to resume duty, or until the matter has been resolved by a medical practitioner".
The controller later reported that he had felt similarly distraught on other occasions and had performed satisfactorily and believed he would be able to do so again. Also, he felt that he had little choice but to return to the operator position. The controller spent 30 to 40 minutes recovering from the meeting and returned to the position after an absence of about 90 minutes.
The centre manager advised the flight information region manager in the operations room and the controller's team leader of the outcome of the meeting. The centre manager briefed the flight information region manager to stand the controller down from operational tasks should there be any doubt about that individual's ability to control. The flight information region manager saw the controller on two occasions during the 40 - 50 minute period following the return to the operating position. The flight information region manager's impression was the controller was managing the position and did not need relief.
Organisational issues
During the last decade, there has been an increased rate of organisational change within Airservices. This has led to increased changes in work practices and a tendency toward expanding many job roles through multiskilling.
Research shows that perceived major causes of stress in Australian workplaces include the rate of change and poor organisational communication. Similar factors were also reported during the investigation.
Despite the strong influence of organisational climate factors on employee stress levels, operational demands also contribute to psychological stress. Also, stress is more likely to be reported where morale is lower than normal.
During 1998 and 1999 the Melbourne Centre was undergoing significant change in preparation for and during the transition to The Australian Advanced Air Traffic Control System (TAAATS). Because of this change, during late 1999 and early 2000 the controller had five different managers. The management of the controller within the centre was such that operational, health and career management and other issues were handled by a number of different managers. This arrangement relied on a high level of coordination and communication between managers for each to maintain an understanding of the progress of staff specific issues. The investigation did not establish the degree to which the controller's issues had been passed on to the relevant individuals during the changeover in management staff.
Air traffic system
Alice Springs sector is a non-radar sector that uses procedural control methods to separate aircraft. Controllers use a combination of a presentation of aircraft positions on an air situation display and lists of electronic flight progress strips to manage and separate aircraft. The air traffic system updates aircraft positions based on limits, including aircraft performance data, meteorological data and the flight data record created for each flight from a flight plan. Controllers update aircraft flight data records after receiving position reports from flight crew.
The label for each aircraft depicted on the air situation display includes a field for operational data. After the controller had been told the A320 had left Alice Springs he annotated the operational data field to show the crew had planned at FL370 and that an amended level of FL270 was needed. When the A320 crew reported on frequency, the controller selected FL270 in the cleared flight level field of the label but told the crew to climb to FL280. When the crew read back FL280 the controller did not detect the error and accepted FL270 in the aircraft's flight data record. Shortly after, the controller deleted the amended FL270 note from the operational data field. Later analysis of the recorded data confirmed the controller had correctly entered FL270 into the system but had issued a wrong level, FL280, to the A320 crew.
The controller had a similar event with a Boeing 737 that left Alice Springs five minutes after the A320 on the same route. The crew of this aircraft also needed to be assigned FL270 to ensure separation from the B767. The controller initially assigned FL280 but corrected it to FL270 during the same radio transmission to the B737 crew. The B737 crew sought clarification of the assigned level from the controller and the controller confirmed the required level was FL270
Pilot - controller communication
Because of very high frequency (VHF) radio coverage limits, air traffic controllers needed to tell crews to change frequency at a position about 250 NM south-east of Alice Springs when operating below FL310. As the B767 was at FL280 the controller told the crew to transfer to 132.9 Mhz, which was a frequency, used by the adjacent Woomera sector. This was to ensure that the crew maintained VHF communications with Melbourne centre. Responsibility for the separation of the flight remained with the Alice Springs sector controller while the crew was monitoring the Woomera sector frequency. The Alice Springs sector controller could not monitor 132.9 Mhz. During the period the crew were monitoring the Woomera sector they did not hear the Alice Springs sector controller tell the A320 crew to climb to FL280. Shortly after, the B767 crew returned to the Alice Springs sector frequency.
The Manual of Air Traffic Services (MATS) states that a reply to a voice call shall consist of the identification of the calling unit, the identification of the called unit and the words "Go ahead" or "Standby" as appropriate. However, while "communications should normally start with a call and reply, when reasonably sure that the call will be received, the calling unit may go ahead without waiting for a reply". In a situation similar to this occurrence, the resulting report from a crew would include the altitude or level being maintained. However, following the B767 crew's on-frequency report the controller immediately told them to report sighting and passing the A320. The controller did not ask nor did the crew report the flight level being maintained.