A Lockheed C-130J Hercules (Hercules) had conducted a practice Instrument Landing System (ILS) approach to runway 35 at Canberra followed by a touch and go landing and departure to the northwest. A Boeing 737-376 (B737) was simultaneously radar vectored for an instrument approach to runway 17. Both aircraft intended to use the same runway surface but in opposite directions. The Canberra Approach East (CBE) controller became concerned that the separation standard of either 3 NM laterally or 1,000 ft vertically would not be maintained between the aircraft and issued turn instructions to both crews. While complying with the instructions the two aircraft passed with approximately 2 NM and 100 ft separation. There was an infringement of separation standards.

The Hercules crew had requested an ILS approach to runway 35 at Canberra for instrument flight rules (IFR) flying training purposes. An ILS is a precision instrument approach that provides centreline and glideslope guidance to the pilot, aligned to the landing runway and is primarily used during periods of low cloud and/or poor visibility. Runway 35 was the only runway serviced by an ILS approach at Canberra. The En Route Supplement Australia (ERSA) required crews planning instrument training at Canberra to contact Canberra air traffic control to book an approach time slot for air traffic control traffic management purposes. The service provider reported that the Hercules was running late and had missed its booked slot.

The CBE controller planned to sequence the Hercules between the second of two aircraft taxiing for a departure from runway 17 and the B737, which was the first of a number of arrivals for that runway. The CBE controller was aware that the Hercules' practice ILS approach might be delayed by up to 45 minutes if he was unable to sequence that aircraft ahead of the B737. The CBE controller stated that he felt some pressure to provide a good service to the Hercules crew.

On first contact with the CBE controller the B737 crew was told to expect a Very High Frequency Omni-Directional Radio Range/Distance Measuring Equipment (VOR/DME) approach to runway 17. At various times thereafter, the crew was assigned radar vectors and a speed restriction of 270 knots indicated airspeed to position the B737 behind the Hercules and provide sufficient spacing to maintain the required separation standard. The CBE controller had asked the crew of the Hercules to maintain their best speed once established on the final approach track. That was a request only and the crew of the Hercules was under no obligation to comply. From that point, the Hercules was capable of maintaining an indicated airspeed between 10 to 20 kts faster than that which it would routinely maintain. The crew of the Hercules could not recall whether they had complied with the request.

The CBE controller was concerned about the application of separation between the B737 and the Hercules after the Hercules had completed its touch and go landing. The Letter of Agreement between the Canberra Tower and Canberra Approach Control stated that the approach controller was responsible for separation assurance during reciprocal runway operations unless it was assigned to the ADC "by mutual agreement". The CBE controller advised that his contingency plan was to instruct the B737 crew to terminate the approach if it became apparent that separation between the two aircraft may be infringed.

The CBE controller reported that he had based the traffic management plan on his expectation that the Hercules would be operated at a higher speed along the final approach path. The CBE controller also reported that the Hercules had commenced its turn later than he had expected following the touch and go landing. He could not see the Hercules on radar following the touch and go landing and was unsure of the position of that aircraft in relation to the B737. The CBE controller asked the ADC to confirm when the Hercules had commenced the turn and was visually clear of the inbound path of the B737. The ADC was unable to provide visual separation between the B737 and the Hercules before radar and vertical separation were infringed.

The CBE controller reported that his workload was very high at the time of the occurrence. He did not provide either crew with a safety alert in respect of the other aircraft, as required by MATS, despite the distance between the two aircraft being less than that prescribed by the applicable separation standards.

Both aircraft were equipped with a traffic alert and collision avoidance system (TCAS). The crew of the Hercules did not receive either a traffic advisory (TA) or a resolution advisory (RA) on the TCAS. The crew of the B737 did not report receiving a TA or a RA either during, or after, the occurrence.

Shortly after departing Melbourne en route to Port Vila, Vanuatu, the crew of a Boeing 737 (B737) aircraft received advice from Air Traffic Control (ATC) that a following aircraft had observed rubber and debris on the runway. As nothing unusual had been noticed during take-off, the flight crew of the B737 considered that the debris was possibly from the BAe 146 ahead of them and asked ATC if the debris could be identified. Assessment by ground engineers confirmed that the debris was a section of the left main landing gear door and tyre tread from a B737.

On receiving that information the crew checked their flight controls for any signs of restriction or abnormal handling. As the left wing trailing edge was checked for damage through the cabin window by one of the cabin crew, a passenger advised her that a bang had been heard from under the wing during take-off. No damage was observed but the flight crew decided to divert the aircraft to Sydney. Approaching Sydney, the crew contacted ATC and requested a gear-down fly-past to assess the condition of the landing gear.

The fly-past confirmed that part of the left main landing gear door was missing but the wheels appeared to be intact. An emergency was then declared and the flight crew consulted the operator's emergency procedures manual. After burning off excess fuel, the cabin crew and passengers were briefed for the emergency. The flight crew then commenced their approach with the cabin crew and passengers in the brace position and an uneventful landing was carried out.

The aircraft was stopped on the taxiway and inspected by ground engineers where it was found that the left outboard tyre had lost its tread but was still inflated, although at a lower than normal pressure. The aircraft was then cleared to taxi under its own power to the terminal and the passengers disembarked normally. Both left main wheels were deflated and replaced. Further inspection of the aircraft revealed damage to the left main gear mid door, the left inboard trailing edge flaps and the underwing false structure. Temporary repairs were carried out to the aircraft and it was flown, without passengers, to a maintenance facility in Melbourne for further repairs.

The investigation revealed that there had been impact damage, marked with black rubber, to the flaps and underwing, and ductile overload damage to the landing gear door tie rod and underwing panel support links. The left outboard main wheel and tyre were sent to overhaul and retread facilities for examination and testing.

An examination of the wheel and tyre showed evidence of air leakage from the bead area and on the tyre surface. After a pressure retention check, the wheel was disassembled and the hub-halves examined with no evidence of damage to the hub seal or mating surfaces found. The tyre liner was found to be intact with no air leakage apparent and there were no signs of delamination of the carcass inner plies. An inspection of the separated surfaces revealed areas of shiny polished rubber. That indicated that there may have been localised ply movement and separation prior to failure.

A blueing of the rubber around the tyre's shoulders and on the separated sections of tread was also noticeable. That indicated that the tyre had been overheating. Factors contributing to overheating can be, low tyre pressures, high taxi speeds, long taxiing or heavy landings. There was no evidence of cuts or foreign object damage on the tyre or tread segments.

The aircraft normally operated with moderate to high payloads and at airports with long taxiways. Both those factors would have affected the temperature of the tyre and increased the importance of maintaining correct tyre pressures. The company's standard operating procedures specified a maximum taxi speed of 30 knots, which was within the tyre manufacturer's limit. An inspection of the operator's maintenance records revealed that the tyres were checked for correct pressure daily before the first flight and every 30 flying hours on an ancillary check. However, the pressures were not recorded if they were found to be within the serviceable limits.

The failed tyre had been fitted to the aircraft for 4 weeks and during that time only one occurrence of lower than normal tyre pressure had been recorded. It was established that the tyre was at its fourth (R4) retread, with that tyre type permitted to have up to seven (R7) retreads. The failed tyre's service history, and the retread and wheel assembly processes were assessed but nothing was found that may have contributed to the tyre failure.

A Boeing 767-336 (B767) was en route from Sydney to Melbourne and was maintaining flight level (FL) 350. A Boeing 737-800 (B737) was en route from Melbourne to Nadi, Fiji, and was also maintaining FL350. The aircraft were on segregated routes that provided lateral separation until the crew of the B737 was provided with track shortening. That decision placed the two aircraft on conflicting flight paths at the same level. The Eildon Weir/Benalla (ELW/BLA) sector controllers saw the impending conflict and alerted the Wollongong/Jervis (WOL/JVS) controller. Both controllers then issued traffic information and instructions to the crews for avoiding action. Both crews received Traffic Alert and Collision Avoidance System (TCAS) Resolution Advisories (RA) and the controllers received a Short Term Conflict Alert (STCA) from The Australian Advanced Air Traffic System (TAAATS). The aircraft passed within 4.8 NM laterally and 800 ft vertically. The required separation standard was either 5 NM laterally or 2,000 ft vertically. There was an infringement of separation standards.

The B737 crew had flight planned, and had been initially cleared to, FL330. That was a standard level for the direction of flight. Levels were assigned depending on a number of factors including the track of the aircraft in accordance with the Table of Cruising levels in the Manual of Air Traffic Services (MATS). Aircraft operating at altitudes and flight levels in accordance with the table were considered to be at standard levels, and those operating at altitudes and levels not in accordance with the tables were considered to be at non-standard levels. The crew of the B737 subsequently requested, and was assigned, non-standard FL350. At the time of the level change, both the crew of the B767 and the crew of the B737 had been issued airways clearances on one-way, designated air routes that formed a segregated race-track pattern between Sydney and Melbourne.

The controller responsible for the ELW/BLA sectors was instructing a student training on the ELW sector. Both were concentrating on the sequencing and separation of two jet aircraft in a step descent into Melbourne. A step descent allowed aircraft to simultaneously descend to vertically separated levels provided that the higher aircraft was progressively assigned levels that provided vertical separation with the lower aircraft. The step descent was occurring in the bottom left quadrant of the controller's Air Situation Display (ASD). The instructor was positioned behind and to the left of the student so that he could readily view the ELW sector and the traffic on the left side of the ASD. The B767 and the B737 were displayed in the top right quadrant of the ASD. Once the step descent had been established, the instructor noticed that the B737 was about to conflict with the B767. By that time the B737 was within the WOL/JVS combined sector and the instructor advised the WOL/JVS sector controller that he would be turning the B737. The student instructed the crew of the B737 to turn right to avoid the opposite direction B767.

The B737 was within the WOL/JVS control area, but under the jurisdiction (and control) of the ELW/BLA controller. The Australian Advanced Air Traffic System Human Machine Interface (HMI) used different coloured tracks and labels to aid situational awareness. The track and label colour of the B737 was green to the ELW/BLA controller, and blue to the WOL/JVS controller. The B737 crew should have been transferred to the WOL/JVS sector prior to crossing the boundary between those sectors and the ELW/BLA sectors. Had the transfer been made the track label and symbol would have been green on the WOL/JVS ASD.

The WOL/JVS controller initiated the amended route clearance for the B737 at FL350, and verbally coordinated the change with the ELW/BLA controller. At that time, the southbound B767 was on climb to FL280. The crew of the B767 contacted the WOL/JVS controller and was assigned FL350. The amended route for the B737 was direct to ALLOC, a waypoint located 77NM east-north-east of Sydney.

The workload on the WOL/JVS sectors at the time of the occurrence was reported by the controller to be low. The controller was providing a directed traffic information (DTI) service to military helicopters operating under visual flight rules (VFR) in class "G" airspace. The provision of DTI to VFR aircraft was available on request and subject to controller workload.

The WOL/JVS controller reported that the ASD at that console had recently "been faulted" and found to be outside the acceptable parameters for contrast. Subsequent to the occurrence, the screen was again checked and was found to be below acceptable contrast parameters. The controller reported difficulty distinguishing the blue track colours from the grey background of the screen; they appeared faded. A track was blue to indicate that the track was about to become the responsibility of that controller. Tracks will appear (in this case) blue to only one console at a time. The same track symbol and label was a different colour to all other controllers to indicate the relevance of that track to each control position.

The WOL/JVS controller stated that a smaller information screen that was open on the WOL/JVS ASD initially obscured the track symbol and label of the B737. He had used the route function available in TAAATS to determine the cleared route of the B737. The controller also stated that he normally used the text message box in TAAATS as a visual reminder of potential conflicts. He did not use the text box on this occasion. He also indicated that he would have preferred using strips because they better facilitated the acquisition and maintenance of the traffic picture.

The ELW/BLA instructor commented that the angle of view from behind and to one side of a student made it difficult to see some areas of the ASD and to monitor keyboard entries.

A Boeing 737-376 aircraft was being taxied for a departure from runway 20 at Christchurch on a scheduled service to Auckland. The Automatic Terminal Information System indicated that the surface wind was from 200 degrees at 10-15 kts, the temperature was 6 degrees Celsius and the dewpoint was 5 degrees Celsius. The visibility was 10 km reducing to 3,000 metres in rain and drizzle. During the taxi, the crew observed that the weather was fine and that the taxiway was wet after recent rain.

The route to the threshold of runway 20 included a 1,600-metre straight section of the main taxiway which ran parallel to runway 02/20, and which had a slight downhill grade. Analysis of flight data recorder (FDR) data revealed that the aircraft was on that section of the main taxiway for 2.3 minutes and that the speed of the aircraft gradually increased from 11 kts until it reached a maximum of 29 kts. The operator's flight crew training manual (FCTM) contained the following information regarding taxi procedures:

"To the pilot, the airplane appears to be moving slower than it actually is due to the flight deck height above the ground. Consequently, the tendency is to taxi faster than desired.

"Taxi speed should be closely monitored during taxi out, particularly when the active runway is some distance from the departure gate.

"Avoid taxi speeds greater than 30 kt on long taxi routes.

"Allow for decreased braking effectiveness on slick surfaces."

Although it was not included in the most recent edition of the FCTM, previous text stated that when approaching a turn, the aircraft should be slowed to the appropriate speed for the conditions. On a dry surface, approximately 8 kt to 12 kt was recommended. The aircraft manufacturer inadvertently removed that maximum recommended cornering taxi speed, when the Boeing 737 FCTM was extensively rewritten.

At the end of the main taxiway, the route to the threshold of runway 20 required that the aircraft be steered to the left, through approximately 60 degrees, onto taxiway "alpha". The pilot in command began braking the aircraft before reaching that turn point, but the aircraft had only slowed to 25 kt when the turn was commenced.

During the turn the nosewheel started "scrubbing", indicating excessive steering angle and/or taxi speed for the surface condition. Lacking traction, the nosewheel moved sideways and directional control was lost. That was followed by loss of traction on the main gear. As the aircraft moved sideways, the right main gear slid off the paved surface and onto the grassed area adjacent to the taxiway. The aircraft came to a halt with the right main gear settled slightly in the soil.

A maintenance engineer attended the aircraft, assessed that there was no obvious damage and then marshalled the aircraft back onto the taxiway. The aircraft was then taxied back to the terminal where a detailed inspection of the landing gear, the brakes and the engines was carried out. That inspection did not reveal any damage and the aircraft was released back into service.

The technical crew of the Boeing 737 consisted of a pilot in command and a co-pilot; both of whom were very experienced on the aircraft type. The airline operator had only recently commenced operations from this airport; the crew's local experience was therefore limited. The Boeing 737 nose wheel steering system was only controllable from the left control seat. Therefore, the pilot in command always taxied the aircraft. Either pilot could have used the ground speed readout on the pilots' electronic attitude director indicator (EADI) to monitor the taxi speed. The airline's normal procedure was for the co-pilot to bring to the attention of the pilot in command, any unsafe speed. During the airline operator's subsequent investigation of the incident, both pilots expressed surprise at the high speed recorded by the FDR during the turn.

The taxiway in question was treated during February 2001 with a surface enrichment treatment that resulted in making the surface more slippery. A notice to airmen (Notam) was issued on 20 March 2001 that advised poor braking action was possible when the surface was wet. That Notam was subsequently cancelled on 27 May 2001, when it was considered that the taxiway surface had weathered sufficiently for friction levels to return to normal.

During August 2001, a different airline operator reported another two minor skid events at that same location. Neither of those incidents resulted in the aircraft leaving the sealed area. As a precautionary measure, the airport operator re-issued the Notam that warned of the possibility of poor braking action. The taxiway surface was subsequently roughened by water blasting. That action removed the smooth bitumen top layer and exposed the aggregate for a better friction surface.

The Cessna Aircraft Company 402C (Cessna) was established on final for a straight-in approach to runway 15 at Cairns. The pilot had been assigned a descent to 3,000 ft, due to a de Havilland Canada Dash 8 (Dash 8) that was on final approach ahead of the Cessna and was at or below 2,000 ft. The assigned altitude ensured that the 1,000 ft vertical separation standard was maintained. The Approach One controller did not notice the Cessna descend through 3,000 ft or that the ground speed of the Dash 8 had reduced such that the spacing between the aircraft was less than the required 3 NM radar separation standard. There was an infringement of separation standards. The weather was reported to be fine with a clear sky.

Cairns approach control was managed by two control positions; Approach One and Approach Two. The Approach One area of responsibility was over the sea and included the final approach for runway 15 and all departures. Approach Two was responsible for the area over land.

The Approach One controller had accepted responsibility for the position about 10 minutes before the occurrence. The controller had been the Flow controller for the afternoon and was due to finish his shift at 1830 Eastern Standard Time. Prior to leaving, he offered to take over Approach One to enable another controller to take a short break. A handover/takeover was conducted at the Approach One position and he was aware of the six aircraft in the arrival sequence; having established the sequence himself while in the Flow position. He was also aware of another four aircraft taxiing for departure.

The initial aircraft in the arrival sequence were a Twin Otter from Mackay, the Dash 8, the Cessna and then an Embraer Bandeirante from the west. The Approach One controller was responsible for the Twin Otter, Dash 8 and the Cessna, while the Bandeirante was under the control of the Approach Two controller.

The Twin Otter crew had been assigned a visual approach for left base to runway 15 but subsequently requested an instrument landing system (ILS) approach. Approval of the ILS would entail additional track miles and reduce the spacing between the Twin Otter and the Dash 8. The controller believed sufficient spacing for separation and sequencing would be maintained with some minor track adjustments. He instructed the Dash 8 crew to turn left heading 330 degrees and to descend to 3,000 ft to position the aircraft east of the coast and 6 miles behind the Twin Otter. About two minutes later the controller instructed the Dash 8 crew to descend to 2,000 ft and the pilot of the Cessna to descend to "3000 (ft) visual". Those instructions were appropriately acknowledged by the crews. As the Cessna was from the north, and effectively on a long final, the controller issued the instructions to establish the vertical separation standard between the aircraft.

The Approach One controller instructed the Dash 8 crew to turn left heading 250 degrees and to descend to 1,500 ft. The crew was aware of aircraft arriving from the north. As the Dash 8 approached the runway 15 extended centreline, the crew thought the approach controller may have forgotten them and they discussed whether or not to contact the aerodrome controller direct. The crew could see the terrain to the west and reduced the aircraft's speed to reduce the rate of closure with the terrain. Shortly after, the Approach One controller instructed them to make a visual approach. That required them to turn the Dash 8 approximately 140 degrees to the left and then turn back to the right to establish the aircraft on final for runway 15. The crew did not report, nor were they required to report, their reduced speed. The controller could monitor aircraft ground speeds via the air situation display radar track labels.

The pilot of the Cessna had been assigned a descent to 3,000 ft and was instructed to maintain the best approach speed. He had been given traffic information on the Dash 8 and was expecting to be instructed to sight and follow that aircraft. Use of the sight and follow procedure by air traffic control (ATC) was common and transferred separation responsibility from ATC to a pilot. The Cessna pilot could see the Dash 8 ahead on final and continued descent below 3,000 ft without a clearance. He later stated that he only became aware that he had not complied with his clearance after he transferred to the aerodrome control frequency. The pilot also said that he believed there was no risk of collision.

The Approach One controller was an experienced controller and was also a team leader. He was on the second shift of a four-day cycle and had commenced the shift at 1100. He had worked the same shift the previous day. The controller had two days off duty before commencing this shift cycle. On the day of the occurrence he had visited a relative in hospital at 0800 and then returned home to do some paperwork before going to work. The relative had entered hospital about a month previously and the controller had visited regularly over that period. The controller was aware of the need to not allow the relative's illness to impact on his work. He believed he had achieved a balance between work and non-work commitments.

The controller spoke briefly with the Approach Two controller and gained the impression that the Cessna was under the control of the Approach Two controller. Consequently, as he saw the distance reducing between the Dash 8 and the Cessna he was waiting for a response from the Approach Two controller despite the fact that both pilots were operating on the Approach One radio frequency.

The Aerodrome controller was concerned with the reduction in spacing between the aircraft, and asked the Approach One controller to slow the Cessna to provide sufficient time for the Dash 8 to vacate the runway. That prompted the controller to ask the pilot of the Cessna if he could see the Dash 8. The pilot replied that he could, and was then instructed to contact the Aerodrome controller, who instructed the pilot to make an orbit, as there was insufficient spacing to ensure that the runway standard would be met.

During the take-off roll, the cabin manager of the BAe 146 aircraft became aware of a smoky, burning smell coming from an air vent in the region of her crew seat at the forward (L1) exit door. Initially there was a mild odour. That was followed by the rapid onset of strong fumes for a short period after which the fumes dissipated quickly. The event was of 2-3 minutes duration.

The cabin manager felt overwhelmed by the fumes and was on the verge of passing out when her colleagues became aware of the situation and provided her with portable oxygen. After approximately 10 minutes of using oxygen, the cabin manager felt well enough to attempt a resumption of her duties but was unable to continue due to the effect of the fumes exposure.

The cabin manager, who had ten years of operational experience on the BAe 146, spent the duration of the flight seated at the rear of the aircraft; breathing portable oxygen for most of that time. The cabin manager reported that when she was not using oxygen she felt unwell, she had difficulty in thinking clearly and she found it difficult to coordinate her thoughts with her actions. No other members of the crew or any of the passengers reported being affected by the fumes.

Upon arrival in Kununurra, engineering inspections were performed on the aircraft and further action was deferred in accordance with the Civil Aviation Safety Authority airworthiness directive AD/BAe146/086. That airworthiness directive required certain actions to be performed whenever a cabin air quality problem was identified, which was suspected of being associated with oil contamination of the air supply from the air conditioning packs. Subsequent engineering inspections revealed that the cause of the oil contamination was a worn number one bearing seal in the number 3 engine. The engine was replaced and no further fumes were evident during following flights.

The cabin manager sought medical treatment and tests in Kununurra on the day of the incident and in Perth on the following day. Although she was eventually cleared to return to work, symptoms of anxiety, impaired judgement, and light-headedness remained with her for in excess of one week. Of note was the result of a blood test that revealed she had been exposed to a higher than normal level of carbon monoxide (CO). When inhaled, CO combines with the haemoglobin, the blood's oxygen-carrying molecule, to form carboxyhaemoglobin (COHb). Once in that state, the haemoglobin is unable to carry oxygen. Thus, the blood's ability to carry oxygen to body tissues, including vital organs such as the heart and brain, is inhibited.

CO is the product of incomplete combustion of carbonaceous material. It is found in varying amounts in the smoke and fumes from burning aircraft engine fuels and lubricants. The gas itself is colourless, odourless, and tasteless but is usually mixed with other gases and fumes that can be detected by sight or smell. Individuals that have been exposed to CO should be removed from the exposure and administered 100 percent oxygen through a tight fitting mask until all symptoms have been resolved. If blood testing for measurement of COHb level is required, the samples should be drawn as soon as possible after the exposure, as COHb has a short half-life in the body of 4-5 hours. If an individual is administered 100 percent oxygen, the half-life is reduced to 40 to 80 minutes.

The same aircraft was the subject of a pilot report three days prior to the cabin manager's experience, in which an oil-like smell was evident in the cockpit but not in the cabin. The event was of short duration and occurred just after take-off, when the source of air supply was changed from the Auxiliary Power Unit (APU) to the engines. Inspection by maintenance engineers of the engines, APU, and air-conditioning system revealed no signs of contamination and the defect was cleared.

Evidence from previous incidents of air system contamination on this type of aircraft has indicated that fumes were associated with engine or APU oil contamination of the air conditioning system. The BAe146 is similar to many aircraft in that the supply of cabin air originates in the aircraft's engines. Air is bled from the final stage of the engine's high-pressure compressor just prior to the combustion chamber. The air destined for the cabin then passes through a catalytic converter in order to clean the air of any oil contaminants. Catalytic converters operate at maximum efficiency under highly specific conditions of temperature and contaminant to air ratio. The air is then passed through a heat exchanger and then through one of two air conditioning packs before entering the cabin. During normal operation bleed air from engines one and two is fed to pack one, which in turn supplies conditioned air to the flight deck and cabin. Bleed air from engines three and four is fed to pack two, which normally only supplies air to the cabin. Additionally, bleed air from the APU is used by either pack during the take-off and landing phases or when air conditioning is required on the ground.

The Boeing 747-400 (B747) was tracking northwest on air route R340 at flight level (FL) 330 and estimated TASHA, a position 61 NM northeast of Mount Isa, at 1530 Eastern Standard Time. The Boeing 737-400 (B737) was tracking northeast on air route J64 at FL330 and estimated TASHA at 1531. The Isa sector controller, located in the Brisbane Air Traffic Control Centre, identified the potential conflict between the aircraft and offered the B747 crew a change of level to FL350. The crew preferred a lower level due to the ability to maintain a greater ground speed; the flight had departed later than scheduled and the crew were endeavouring to make up time en route.

At 1501, the controller instructed the B747 crew to descend, when ready, to FL310 with a requirement to reach that level by 31 NM southeast of TASHA. That position was the lateral separation point between the air routes and the controller required the 2,000 ft vertical separation standard to be established between the aircraft before they entered the area of conflict. The pilot in command (PIC) readback the amended clearance in accordance with Aeronautical Information Publication (AIP) procedures. Subsequently, the crew did not descend the aircraft in accordance with the clearance and it entered the area of conflict at FL330. There was an infringement of separation standards as the required vertical standard was not achieved before the aircraft entered the area of conflict.

At about 1508, a change of controllers occurred at the Isa sector position. The new controller instructed the B747 crew to change frequency at 1512. The crew contacted the Isa controller on the new frequency and reported maintaining FL330. The AIP required a crew operating in controlled airspace to report, after any en route frequency change, the last assigned level and whether the aircraft was on climb, in the cruise, or on descent. The crew did not report the assigned level of FL310 and the controller did not query the crew regarding that report.

The controller became concerned, as the B747 approached the lateral separation point, by the lack of a report indicating that the aircraft was on descent to the amended level. The AIP required a report from a crew when an aircraft had left a level at which level flight had been conducted in the course of a climb, cruise, or descent.

The controller conducted a single interrogation (one shot) of the aircraft's automatic dependant surveillance (ADS) system and attempted to contact the crew by very high frequency (VHF) radio. Automatic Dependant Surveillance was a system dependant on a datalink and a series of reporting `contracts' (a rate of reporting) established between an aircraft and a ground system. The Australian Advanced Air Traffic Control system (TAAATS) automatically initiated contracts and specified the type of report, the content of a report, and the reporting frequency required. As the contracted reporting occurred automatically, it required no flight crew action. There was no cockpit indication that a "one shot" request had been actioned by an aircraft's ADS system.

The ADS response from the aircraft at 1527 indicated that it was maintaining FL330 and was 26 NM from TASHA, within the area of conflict. The controller again attempted to contact the crew by radio and also by the controller pilot datalink (CPDLC) facility. The controller made another "one shot" interrogation of the aircraft's ADS. That ADS response at 1529 indicated that the aircraft was at FL329 and 14 NM from TASHA.

Flight crews were required to maintain continuous communications with air traffic control while in controlled airspace and within VHF radio coverage. Crews of ADS equipped aircraft were able to report to ATC using that facility; however, they were required to communicate using VHF radio when operating within radio coverage. The B747 was operating in non-radar airspace and the crew reported their position via ADS. The route was within VHF radio coverage for the sector.

The controller was about to instruct the B737 crew to climb to FL340 when an ADS altitude report of FL312 was received from the B747. That report established that the 2,000 ft separation standard had been achieved as it was within 200 ft of the assigned level.

At 1529:43, after five unsuccessful attempts to contact the B747 crew on VHF radio, the controller asked the crew of the B737 (on the crossing route) to contact the B747 crew and have them call on 125.2 Mhz. At 1531, the B747 crew contacted the controller on the VHF radio and reported maintaining FL310. At the same time the B747's ADS issued a Waypoint Report for TASHA which reported the aircraft's level as FL309. Later analysis of the ADS reports indicated that the B747 had descended 1,700 ft in about 28 seconds.

The automatic reporting rate for ADS tracks was set by TAAATS. The flight information region was divided into cells that were allocated a reporting rate for a Basic Report. The rate was normally 30 minutes (or 40 minutes for oceanic areas). A controller with the jurisdiction of an aircraft on an ADS track can manually amend the rate as required. Also, when the aircraft passed a designated waypoint the system automatically generated a Waypoint Change Event report that was appended to a Basic Report. Furthermore, an Altitude Range Event report was automatically generated when an aircraft left a contracted vertical range. When in the cruise, that vertical range was plus or minus 200 ft of the cleared flight level (CFL). Assignment of an amended level reset the range. When on climb, the reset range was the present level minus 200 ft to CFL minus 200 ft, with the reverse range for aircraft on descent. At that time, for the B747 maintaining FL330 and then assigned FL310, the vertical range would change from FL332 - FL328 to FL332 - FL312. As the aircraft descended through FL312 the Altitude Range Event report was generated and the contract reset to FL312 - FL308; to monitor the amended CFL (FL310).

The B747 PIC later reported that they had endeavoured to remain at FL330 for as long as possible due to turbulence at FL310 that would have likely required a speed reduction, which in turn, would have constrained their efforts to make up time during the flight. At the time of the issue of the amended clearance, the PIC was the pilot flying the aircraft and the first officer had left the flight deck shortly before to take a break. On the return of the first officer, the PIC briefed him on the clearance as per company procedures and the FO wrote the clearance on the flight plan. The incident report submitted by the crew stated that the annotations used by the FO on the flight plan indicated that descent should commence at 31 NM from TASHA, instead of the requirement to be at FL310 at that point.

The crew then became involved in troubleshooting a problem with balancing the main fuel tanks. The PIC stated that they had been distracted and forgot about the requirement to descend to FL310 by 31 NM southeast of TASHA. The PIC reported that he was aware of the B737 on the crossing track as he had heard the controller request the B737 crew to contact them (the B747 crew).

The South Pacific Air Traffic Services Coordinating Group's Southern Pacific Operations Manual (SPOM) V3.1 set the standard for ADS operations for air traffic control service providers and operators. The system status and serviceability was checked following the occurrence. Between 1332 and 1719 there were 31 downlink messages of which the minimum transit time was 6 seconds and the maximum transit time was 24 seconds. Those times were within the required SPOM system performance parameters. During that period there were no reported failures of the communication or TAAATS systems.

The investigation did not establish why the B747 crew did not respond to the controller's radio calls.

The Sikorsky S76C helicopter was in cruise flight with the automatic flight control system engaged, when the flight crew noted a loud noise and the helicopter yawed to the left, rolled left, and the nose pitched down. The flight crew disengaged the automatic flight control system and resumed flying the helicopter manually, stabilising it in level flight. The right engine-out and fire-warning annunciators were illuminated, with the engine-out aural warning sounding. The right engine instruments displayed zero rotational speed of the gas generator (GG) and extremely high turbine outlet temperature (measured at point T4 within the engine). The crew activated the right engine fire bottles and simultaneously closed the fuel firewall shut-off valve. The fire indication extinguished. They then configured the helicopter for single engine flight with the remaining engine operating approximately ten seconds into the two and one-half minute One Engine Inoperative (OEI) limitation. The flight crew adjusted power requirements for the OEI condition and then completed an uneventful single engine landing at their Longford base.

Examination of the helicopter revealed minor shrapnel damage to the right engine exhaust extension, and fracture separation of the engine oil pressure switches and rear bearing external oil vent and return pipes.

The Turbomeca Arriel model 1S1 engine comprised five modules. Module three (or the high-pressure section) contained the gas generator first and second stage wheels. The left side of the right engine, forward of the external rear bearing oil return line near the outer surface of module three, displayed evidence of fire and oil residue.

The right engine was removed and shipped to the engine manufacturer's Australian facility for disassembly and examination with Australian Transport Safety Bureau (ATSB), operator, and engine manufacturer representatives in attendance.

Engine examination

Disassembly and preliminary examination of Arriel 1S1 engine, serial number 15038, revealed a separation of one GG second stage turbine blade. Blade number sixteen was separated above the blade 'fir tree' attachment point, below the blade platform, and had punctured the second stage nozzle guide vane turbine ring. The rear bearing of the GG had collapsed and was significantly damaged. Separated pieces of the centrifugal diffuser of module three were found inside the module. There were indications that several fracture surfaces of the separated sections were pre-existing before the incident. In addition, the engine exhibited signs of severe overheating and significant damage in the air path downstream of the turbine blade separation.

The fracture surface of the separated blade was typical of ductile tensile overload, with the exception of the small corner area of fatigue cracking. The dendritic patterns within the fracture were indicative of the normal underlying microstructure of the blade casting. Failure of the blade in that mostly ductile overload manner indicated exposure to a transient or sustained stress level above the ultimate strength of the blade material at its operating temperature. Refer to ATSB Technical Analysis Report 200103038 (BE/200100017) for further details.

Engine history

The engine was installed on 4 March 2000 and had accumulated 7,935.0 hours and 6,784.1 cycles since new. It had been overhauled on 12 February 1999, and had accumulated 1,992.0 hours time since overhaul (TSO) and 1,878.1 cycles since overhaul. The GG assembly second stage turbine disc, serial number DC3666YC, had been installed during the overhaul with zero hours and cycles accumulated. The turbine disc and blades were well within the life limit of 10,000 cycles established by the manufacturer. Arriel engine modification TU204 (GG turbine blade plasma coating) had been incorporated.

Previous Australian occurrences

Occurrence report 200100584

On 7 February 2001, a Sikorsky S76C helicopter belonging to the same operator, with two crew and ten passengers on-board, was in a hover with the flight crew completing before take-off checklist items. The pilot reported that while trimming the engines, a "pop" was heard. He then noted that the left engine turbine gas temperature (measured at point T4 within the engine) was in excess of 1000 degrees C. The helicopter was then landed uneventfully. The flight crew reported that the only cockpit indication of imminent failure was the almost simultaneous illumination of the left engine chip (magnetic particle) detector advisory.

Examination of the helicopter revealed minor shrapnel damage to the left engine exhaust extension and engine cowling. There was no reported engine fire. The left engine was removed and sent to the engine manufacturer for disassembly and examination. The manufacturer's final report noted a separation of turbine blade number six of the GG second stage disc. The blade was separated above the 'fir tree' attachment point but below the blade platform, and had punctured the second stage nozzle guide vane turbine ring. One adjacent blade (number seven) in the direction of turbine wheel rotation was also noted as cracked.

Metallurgical examination by the manufacturer attributed the blade failure to a low-cycle fatigue cracking mechanism. The manufacturer concluded that abnormal loading was the major contributing factor in the failure, given the reported absence of anomalous material features or evidence of high-temperature operation. Dimensional inspections failed to reveal any sign of non-conformity that could have led to the development of the abnormal loads. However, the manufacturer stated that turbine blade platform/GG disc interferences were also a potential factor that could have aggravated the fatigue failure of the blade.

At the time of the occurrence, Arriel 1S1 engine, serial number 15522, had accumulated 4,737.4 hours and 4,471 cycles since new. It had accumulated 1,740.0 hours TSO and 1,615 cycles since overhaul. Following overhaul, the engine was installed on March 11, 1999. Module three did not have turbine blade plasma coating modification TU204 incorporated.

Occurrence report 199602839

On 9 September 1996, a Sikorsky S76C helicopter belonging to the same operator, experienced an in-flight engine failure of the right engine while taking off from an oil platform. A loud noise was heard before the engine failure. The right engine was shut down and the crew completed an uneventful single engine return to the Longford base. There was no reported associated engine fire. The right engine was removed and sent to the manufacturer for disassembly examination.

At the time of the occurrence, Arriel 1S1 engine serial number 15513, had accumulated 2,282.0 hours and 1,949 cycles since new. The manufacturer provided the operator with a final report noting the rupture (separation) of one GG turbine blade with subsequent rear bearing damage and GG seizure. Their report stated that the separation was suspected to be the result of blade rubbing with the second stage nozzle guide vanes with no signs of fatigue or abnormal over temperature operation. Module three had turbine blade plasma coating modification TU204 incorporated.

Other overseas occurrences

The French airworthiness authority, Direction Generale de l'Aviation Civile (DGAC), reported knowledge of three other overseas occurrences involving GG second stage turbine blade separation failures. Of those three incident engines, all had the TU204 modification. Cycles since overhaul on those incident engine turbine discs and blades varied from 1,978 to 5,933 cycles.

Engine service bulletin history

Turbomeca Service Bulletin (SB) 292 72 0151 was originally issued on 5 June 1992 specifying the incorporation of modification TU204, the protection of the GG second stage turbine blades from corrosion or erosion with a Heurchrome low pressure plasma coating. That modification also permitted a performance improvement by allowing the more accurate machining of the turbine tip diameter to control the tip clearance. The service bulletin addressed all Arriel variants, with Arriel 1S1 engines having incorporated TU204 from the first production engine. For all other variants, TU204 implementation was optional and installed at the customers' request.

In July 1998, the engine manufacturer implemented internal documentation and procedures to remove all GG turbine blades with TU204 installed during overhaul of module three. Consequently, SB 292 72 0151 was amended on 18 August 2000, to recommend removal of all TU204 modified blades, citing possible weight mass increases and suspected increased stress on the turbine blade root. The manufacturer stated that if the plasma coating was not applied as per drawing requirements, the resulting stresses could be more than anticipated, resulting in abnormal loading of the blade root. Both incorporation and removal of modification TU204 required removal of the engine and/or module and shipment to the manufacturer.

External oil pipe description

Three external oil related pipes provided lubrication of the GG rear bearing. Those pipes passed through hollow support struts and were then physically secured to module three. The supply oil pipe provided oil from the engine driven gear type oil pump to the bearing after passing through a restrictor and a tube screwed into the bearing housing. Oil was then sprayed onto the bearing. After lubricating the bearing, the oil fell by gravity to the bottom of the housing, through a tube and was returned to the tank through an oil pipe to the scavenge pump. The air/oil mist that resulted from the lubrication of the bearing was vented overboard through a vent pipe attached to the top of the housing.

Engine oil flashpoint/autoignition

The engine oil temperature of a normally operating Arriel 1S1 engine in a S76C helicopter was approximately 100 degrees Celsius (C). The flash point of the turbine engine oil was approximately 223 degrees C. The flash point of a liquid was defined as the lowest temperature at which a material would produce a flammable vapour, and was a measure of the volatility of the material.

The auto-ignition temperature of engine oil was approximately 388 degrees C. Auto-ignition temperature was defined as the temperature at which auto-igniting materials spontaneously combust. According to the engine manufacturer, during normal operation, the external surface temperatures of number three modules ranged between 280 to 450 degrees C, dependent upon location on the module, with a maximum surface temperature of 450 degrees nearest the rear bearing. The surface temperature maximum values of module three were well within the auto-ignition temperature of the engine oil.

A Saab SF340B aircraft (Saab) departed Tamworth aerodrome and was tracking to the southeast on climb to flight level (FL) 120. A Mooney Aircraft Corporation M20J (Mooney) was travelling in the opposite direction en route from Bankstown to Inverell via Scone and Tamworth at 8,500 ft. The Mooney was in Tamworth class "C" controlled airspace. The Saab crew received a traffic alert from that aircraft's traffic alert and collision avoidance system as the Saab was approaching 8,000 ft. The Saab crew levelled their aircraft at 8,200 ft and rolled the aircraft to the left to avoid the Mooney. The pilot of the Mooney did not request or obtain an airways clearance from the Tamworth Aerodrome Controller (ADC) to enter Tamworth control area prior to the occurrence. The Saab passed within 1.8 nautical miles (NM) horizontally and 300 ft vertically of the Mooney. The required separation standard was either 1,000 ft vertically or a minimum horizontal distance determined using the appropriate "Lateral Separation" table in the Manual of Air Traffic Services (MATS). There was an infringement of separation standards.

Tamworth Air Traffic Control (ATC) provided a non-radar, or procedural control, service to aircraft operating within the Tamworth control area and control zone (CTR). Controllers used non-radar information to establish and maintain procedural separation standards in accordance with MATS. Tamworth class "C" control area steps extended to 36NM when above 6,500 ft AMSL to the south-southeast of the Tamworth aerodrome in the area that encompassed the flight path of the Mooney. Class "G" non-controlled airspace surrounded the Tamworth CTR and control area.

The Saab crew was conducting a scheduled fare-paying passenger flight under instrument flight rules (IFR) and had been cleared by the Tamworth ADC to climb to FL120. The standard altitude Tamworth ATC could assign to aircraft leaving Tamworth control area and entering the overlying Brisbane sector in accordance with the letter of agreement between Tamworth ATC and Brisbane ATC, was FL120 (subject to other aircraft). Otherwise, a procedural separation standard was applied by Tamworth ATC and coordinated with the Brisbane sector controller, or responsibility for separation was specifically assigned to the Brisbane sector controller.

The pilot of the Mooney was an IFR pilot and was normally provided with radio frequency management instructions by ATC along the route. On this flight however, the pilot of the Mooney was operating under visual flight rules (VFR) and no such advice was provided. All aircraft crews that planned to enter class "C" controlled airspace, whether operating under IFR or VFR, were required to establish two-way radio contact with ATC and obtain an airways clearance prior to entering class "C" airspace. The Tamworth visual terminal chart (VTC) depicted the lateral boundaries of class "C" control area surrounding Tamworth aerodrome above 4,500ft AMSL. However, neither the VTC nor the Aeronautical Information Publication (AIP) En-Route Supplement Australia (ERSA) specified the vertical boundary between Tamworth control area and the overlying Brisbane sector. The pilot later reported that he had studied the Jeppessen low altitude en-route chart relevant to Tamworth, prior to the flight, and believed that he would not require an ATC clearance to enter Tamworth control area above 6,500ft AMSL.

Airservices Australia reported that the Brisbane sector controller had seen the occurrence on that controller's air situation display (ASD) in the Brisbane Air Traffic Services Centre and had received a short term conflict alert (STCA) from The Australian Advanced Air Traffic System (TAAATS). The Brisbane sector controller reported that STCA's between aircraft operating within Tamworth control area were common but did not necessarily indicate a potential infringement of separation standards. Short term conflict alerts, in those circumstances, occurred when the procedural separation standard being used by Tamworth ATC was less restrictive than the STCA activation parameters used in TAAATS.

Although the track symbol and a label, showing the secondary surveillance radar code and the altitude from the Mooney, were displayed to the Brisbane sector controller on the ASD, the Brisbane sector controller had no control or jurisdiction over the Mooney and was not aware that the pilot had not established two-way radio contact with Tamworth ATC. The Brisbane sector controller was also not aware that the pilot had not received an airways clearance to enter Tamworth control area. The Brisbane sector controller believed both aircraft were under the control of Tamworth ATC because both aircraft were within the Tamworth control area. The Tamworth ADC was unable to provide a separation service to the Saab in relation to the Mooney as he had no information on that aircraft.