The SAAB SF 340's departure from Wagga airport had been delayed for 4.5 hours due to ground fog. As the aircraft taxied for departure, the crew completed the pre-flight checks. Incorporated within these checks was the requirement for a "first flight of day" propeller governor overspeed test. As it was the aircraft's first flight for the day, the check was carried out.

Following take-off, and shortly after landing gear retraction, with the Constant Torque On Take-off system engaged, the crew noted that the right engine propeller RPM was low; at approximately 1,100 RPM. The left propeller was within the normal operating range at an indicated 1,378 RPM.

As a return to Wagga was unavailable, due to ground fog, the crew contacted air traffic control indicating their intention to divert to Albury Airport. An Alert Phase was declared and Albury Emergency Services were on stand-by for the aircraft's arrival.

The crew then carried out the appropriate abnormal checklist actions for a propeller underspeed, shutting down the right engine just prior to the top of descent. During that time, the crew briefed the cabin attendant on the engine problem, before informing the passengers of the situation via the aircraft's public address system. Following an uneventful single engine approach and landing, the Alert Phase was cancelled.

An investigation by the aircraft's operator, included analysis of the aircraft's flight data recorder readout. The analysis indicated that during taxi the right propeller RPM had reduced from 1,040 to 990. That RPM drop was consistent with the crew carrying out the propeller governor overspeed test. However, unlike the left propeller, the right propeller RPM had not fully recovered at the completion of the check.

Both crew members reported that on completion of the propeller overspeed governor checks, once they had observed the propeller indications returning towards normal, their attention was diverted towards other checks. The crew also indicated that during the take-off they did not normally check the propeller RPM indications, instead monitoring the engine parameters of "torque and inter-turbine temperature". Consequently, the low right-propeller RPM had not been initially detected.

During the take-off roll the crew noted that the right engine torque had lagged behind the left. That was considered to be due to not having the right power lever pushed far enough forward, as the Constant Torque On Take-off system only engages after advancing the power lever past 64 degrees. The crew had then pushed the right power lever further forward in order to equalise both engine torque indications.

After the flight, the operator completed a thorough maintenance check of the right engine and propeller systems. No unserviceabilities were found during that check. Following consultation with the aircraft's engine manufacturer the aircraft was returned to service. The problem did not re-occur.

The operator attempted to replicate the problem in their SAAB 340 flight simulator. That attempt was observed by a representative from the Civil Aviation Safety Authority. After thorough investigation, the operator was unable to repeat the occurrence.

During climb-out from Darwin, passengers on the British Aerospace Bae146 advised the cabin manager that about 3 metres of cable was trailing from the trailing edge of the right wing. After the first officer had conducted a visual inspection, the crew advised Darwin ATC that they had a problem and required a return for landing. Fuel was burnt off to achieve maximum landing weight. Controllability checks found no handling problems with the aircraft, which was landed safely.

An inspection identified the trailing cable as an aileron trim cable (upper). Failure of the cable had occurred at the outboard pulley located at wing rib 14. The cable was found to have failed as a result of significant corrosion between the pulley bank and the wing rear spar. Corrosion was also present on the failed cable coinciding with the location of the inboard pulley at wing rib 14. No corrosion was found on the left-wing aileron trim cables. Previous inspection of the area was reportedly carried out during a 6C check in May 1999, 3,495 flight hours earlier.

The aileron trim cable material was zinc coated carbon steel (MIL-W-83420, Type 1, Composition A). Stainless steel trim cables were not available from the aircraft manufacturer.

No other reported failures of BAe146 aileron trim cables were found in a search of the Civil Aviation Safety Authority major defect and ATSB incident databases. The operator advised that corroded cables and seized pulleys at that location had been recorded on various BAe146 aircraft since 1992. The aircraft maintenance manual required special attention for corrosion during inspection of cable sections in contact with pulleys.

History of the flights

A Metroliner had departed Darwin on a flight to Dili, East Timor. The crew had climbed to flight level (FL) 180 and were maintaining that altitude. They had been under the control of Darwin Air Traffic Control for the first 60 NM and had transferred to Brisbane Control in accordance with normal procedures. They had established two-way radio communication with Brisbane sector control.

The Airbus A330 (A330) was on a flight from Kuala Lumpur, Malaysia to Darwin and the crew had commenced descent to FL210 in accordance with instructions from Brisbane Control.

When the A330 was approximately 97 NM from Darwin, the crew requested further descent. The Brisbane controller immediately activated the intercom line to Darwin Approach and informed the Darwin controller of the position of the A330. The Metroliner was 81 NM from Darwin at that time.

The Darwin controller, who was under training, only had access to a 60 NM radius display screen. He had already handed off the outbound Metroliner to the Brisbane controller and authorised descent to FL 120 for the A330 in the belief that the Brisbane controller would separate the two aircraft. The trainee was not immediately aware of the relative positions of the aircraft as the conflict was not shown on his display.

The training officer immediately realised that separation had not been assured by the coordination interaction and looked to one side where he had set up a second screen display on an adjacent console. He had selected a greater range scale on the console, that showed the position of the two aircraft. As he was briefing the trainee on urgent action to remedy the situation, the crew of the A330 reported on the Darwin Approach radio frequency that they were on descent to FL120. While that radio exchange was occurring, the trainee had selected the longer range scale on his console and the display had now appeared on his screen. It showed that the aircraft were approximately 9 NM apart in a nose-to-nose conflict. He immediately issued an amended instruction to the crew of the A330 to maintain FL190. The crew was able to carry out that instruction before the vertical separation standard of 1,000 ft was infringed.

A few moments later the captain of the Metroliner saw the A330 pass immediately overhead. He reported that there was insufficient time to draw the co-pilots attention to the aircraft before it passed. He was of the opinion that there would have been insufficient time to initiate an evasive manoeuvre if it had been required.

The A330 crew saw the Metroliner but took no action as the aircraft were obviously going to miss. The traffic alert and collision-avoidance system was serviceable but did not activate.

Radar analysis indicated that the aircraft passed with approximately 1,300 ft vertical separation but with no horizontal difference.

At the Brisbane sector console, the short term conflict alert activated approximately 20 seconds prior to the time of passing. The controller immediately checked the radar display and found that a separation standard was being applied by Darwin approach control and took no further action.

Darwin approach control

The Darwin approach unit controlled airspace to 60 NM, in the north-west quadrant, up to and including FL200. At the time of the coordination from Brisbane sector, both aircraft were outside those parameters and, therefore, not subject to direct control by Darwin.

Local procedures required that arriving aircraft be assigned no lower than FL210 by Brisbane Control. Therefore Darwin Control was required to approve any further descent despite the aircraft being in Brisbane's airspace. When the Brisbane controller coordinated the position of the A330, the trainee read into the tone of the voice that a request was being made for further descent even though the actual words used did not state that intent. The trainee was not immediately aware of the confliction because it was outside his area of jurisdiction and not within the range of his selected display. The trainee also had the impression that, as the aircraft were in Brisbane's airspace, he was only approving descent in Darwin's airspace and that the Brisbane controller was still responsible for the separation of the aircraft.

Radar hand-off was the subject of a specific instruction in the Manual of Air Traffic Services Supplement (MATS Supp) which stated: "Aircraft handed off by radar between Darwin ATC and Brisbane/Tindall Sectors shall be subject to `no restrictions' unless otherwise advised."

The adjacent console was not in use and had been positioned so that the controllers could view the display screen, albeit at a distance of 2 - 3 m. The range was selected at a longer distance than the 60 NM in use at their primary screen. That selection meant that the position of the aircraft could be seen but the details in the information blocks could not be read. A software change was scheduled for introduction the next day that would have allowed the trainee to view the longer range (second look) on his own console rather than having to look across to the second screen.

When the trainee had approved descent for the A330, the Brisbane controller de-selected the intercom line before the training officer could intervene to cancel the approval. The training officer immediately briefed the trainee to maintain the A330 at FL190 because he expected the crew to change frequency quickly as, in his experience, they normally did. The training officer was prepared to go back to Brisbane via the intercom line, but the broadcast by the crew of the A330 made that option redundant.

Brisbane sector control

The controller coordinated the position of the A330 with Darwin Control and expected an instruction from Darwin regarding descent. When they issued approval for FL120 he assumed that they were separating the aircraft, even though he thought that he may not have looked at his display at the time of carrying out the coordination and may have, momentarily, overlooked the actual position of the Metroliner. He then issued the descent instruction and told the crew to change radio frequency to Darwin Approach.

Shortly after, the short term conflict alert activated and the controller immediately checked the display. He saw that there was no infringement of separation standards and took no further action.

The controller had been rated on The Australian Advanced Air Traffic System (TAAATS) for 4 months but had just returned from a month's leave. He received 2 days familiarisation and had performed 4 active shifts prior to the occurrence. He stated that he was well rested and that the workload was moderate. However, he said that he was a bit `rusty' and that the 2 days familiarisation was a bare minimum for adequacy.

Short term conflict alert

The activation of the alert was to warn the controller that the aircraft were predicted to pass within 600 ft and 4.1 NM. Analysis of the performance of the alert indicates that it operated in accordance with the parameters and provided approximately 20 seconds warning of the conflict.

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.