A Boeing 737 (B737), VH-TJT, was en route from Darwin to Adelaide via air route J187 at flight level (FL) 370. Another B737, VH-CZN, was en route from Ayers Rock to Sydney via air route G222, also at FL370, which was a standard level for the direction being flown by both aircraft. The air routes converged, and eventually crossed at Oodnadatta. Both aircraft were under procedural (non-radar) control by Melbourne Sector 1. The sector console was staffed by a controller who was undergoing re-familiarisation prior to being checked for return to controlling. He was being supervised by a controller who had recently returned after a six month break from full-time operational controlling.

The controller had calculated estimates for Oodnadatta of 1518 and 1520 respectively for CZN and TJT. At 1515, when the crew of TJT reported at SARAH, 40 NM north-north-west of Oodnadatta, the controller became aware that there was no separation standard being applied between the two aircraft, so he instructed the crew of TJT to descend immediately to FL350. The crew reported on descent and indicated that their traffic alerting and collision avoidance system (TCAS) showed an aircraft 33 NM ahead, over Oodnadatta. The crew of TJT subsequently reported maintaining FL350 at 1520. As a result, there was a breakdown of the required vertical separation standard of 2,000 ft.

Both controllers had earlier noted the possibility for conflict between the two aircraft and annotated their respective flight progress strips with an Oodnadatta position, and the calculated estimates for that position. The estimates were annotated at different locations on the strips. There was no local instruction for the standardisation of the annotation of the Oodnadatta position or similar positions that marked the intersections of the various route crossings in the area. During the following 90 minutes, the traffic level steadily increased and the two controllers had discussed the need for a coordinator. The sector was normally operated as a solo operator position; however, there were periods when there were significant or complex traffic levels and there were procedures to enable the controller to be assisted by a coordinator in such cases.

Approximately 10 minutes prior to the occurrence, the controllers requested the assistance of a coordinator and as a consequence, a third controller joined them at the console. At this stage, the traffic situation was very busy, with approximately 70 flight progress strips being monitored and with additional strips being discarded or added to the board as flights progressed through the sector. The coordinator controller had little opportunity to obtain an adequate handover/takeover brief from the two controllers already at the position. The third controller assumed the coordinator position and endeavoured to action any items that he considered required attention as he attempted to gain some idea of the traffic disposition. He was unable to monitor the Sector 1 controller's air-ground-air program on a continuous basis due to the conduct of coordination actions. The work at the console was difficult, with three controllers working in an area normally used by only two controllers.

As a result of a combination a factors, the potential confliction between CZN and TJT, although recognised earlier by both controllers, was subsequently overlooked as the sector workload increased. It was only when the crew of TJT reported at SARAH that action was undertaken resolve the situation.

Airservices Australia carried out an investigation of this occurrence under the overall supervision of a Bureau officer. The significant factors that contributed to this occurrence were found to be;

1. The two controllers manning the Sector 1 position were not operating at their optimum level of performance due to a lack of recency.
2. Following an increase in Sector 1 traffic density, the controllers' recognition that they required coordination assistance to manage the increased workload was too late to provide any effective relief.
3. The amount and disposition of traffic in the sector led the controllers to be distracted to a point where they were unable to adequately monitor all sector traffic.
4. The controllers' annotation of flight progress strips did not alert them to the possibility for a conflict between CZN and TJT.

Whilst taxiing for a night departure, the right propeller was struck by a large bird, resulting in the separation of one propeller blade. The ensuing vibration caused substantial damage to the engine mountings and firewall, before the engine could be shut down.

A technical analysis determined that the blade had failed in overload about 15cms from the blade root whilst the propeller was in fine pitch. There was no evidence of any pre-existing cracking or defects in the area which may have contributed to the failure.

The blade had completed 10,228 hours of operation since new and 3,805 hours since last overhaul. The aircraft records indicated that there were no outstanding maintenance requirements on the propeller. The blade complied with all propeller certification requirements.

Witnesses described the bird carcass as that of a Brolga. This species grows to a height of 0.7 to 1.3 metres with a mass of 10 to 15 kilograms.

While climbing through 7,000 ft the engine indicating system, low oil pressure caution light, illuminated. With the oil pressure indication fluctuating around 90 pounds per square inch, and the caution light flickering, the pilot in command reduced power and elected to return to Port Augusta. During descent the warning light continued to flicker, changes in power setting having no effect. As the aircraft turned on to base leg, the warning light became steady and the oil pressure dropped to less than 60 pounds per square inch. The aircraft made an uneventful landing. Shortly after touchdown, the oil pressure returned to 100 pounds per square inch and the caution/warning lights extinguished.

Investigation by maintenance personnel resulted in an oil filter change due to suspected carbon contamination. The aircraft was then returned to service. The operator raised the recurring oil pressure fluctuation problems with the engine manufacturer.

The Pratt & Whitney PT6 engine model installed in the PC12 has experienced episodes of oil discolouration, and carbon particles in the oil. The discolouration was traced to the coatings in the magnesium gearbox, and the carbon was traced to the No. 2 bearing area.

Further investigation of the fluctuating oil pressure indications revealed a fault in the main engine wiring loom.

History of the flight

A Shrike Commander departed Horn Island on a charter flight to Saibai and Boigu Islands in accordance with the visual flight rules (VFR). The flight to Saibai took 32 minutes, and a further 13 minutes to Boigu Island. The aircraft then departed Boigu to return to Horn Island with an expected flight time of 35 minutes.

The pilot reported that he had maintained 5,500 ft until commencing descent at 35 NM from Horn Island. He tracked to join final approach to runway 14 by 5 NM, reducing power at 1,500 ft. At 5 NM from the runway, the pilot extended the landing gear and approach flap and commenced a long final approach.

When the aircraft was approximately 3 NM from the runway both engines commenced to surge, with the aircraft initially yawing to the right. The pilot commenced engine failure procedures and retracted the flaps. He tried a number of times to determine which engine was losing power by retarding the throttle for each engine, before deciding that the right engine was failing. The pilot shut down that engine and feathered the propeller. A short time later, when the aircraft was approximately 200 ft above the water, the left engine also lost power. The pilot established the aircraft in a glide, advised the passengers to prepare for a ditching, and transmitted a MAYDAY report on the flight service frequency before the aircraft contacted the sea. The aircraft quickly filled with water and settled on the seabed. All five occupants were able to escape and make their way ashore.

Wreckage and impact information

The aircraft ditched approximately 400 m short of the threshold of runway 14, and settled in 2.5 m of water. It was subsequently recovered for examination. Although the aircraft had been damaged during the ditching, it remained essentially intact. The fuselage was distorted in front of and behind the cabin area as a result of impact forces. The underside of the fuselage had also been pushed upwards, and both windscreens were broken. The fuel tanks were intact, and the fuel tank vents were not obstructed.

Personnel information

The pilot in command had gained a commercial pilot licence in 1994, and worked as a flight instructor until April 1998. He had been based at Horn Island since April and was subsequently appointed as the company chief pilot on 11 September 1998. Two days prior to his appointment he had been endorsed on the Aero Commander. At the time of the occurrence, the pilot had accumulated a total flying experience of 2,045 hours, including 566 hours on multi-engine aircraft, and 79 hours on Shrike Commander aircraft.

Aircraft information

The aircraft had undergone scheduled maintenance in Cairns on 28 August 1998, and had since flown 100.8 hours. The next scheduled maintenance was due in 19.2 hours. The horizontal situation indicator was unserviceable and had been placarded as such, with the defect being recorded in the maintenance release; however, that did not preclude the conduct of VFR flight.

No defects that could have contributed to the accident were found in the airframe or flight control systems. An examination of the engines and their associated systems did not reveal any defects that could have led to the loss of power. The right engine fuel control unit was found to be serviceable but worn. Bench tests indicated that it provided a fuel flow 10% greater than normal (approximately 6 L/h).

The right propeller had been feathered before the ditching; however, the propeller blades had not moved to the fully feathered position. Examination of the propeller dome revealed that oil sludge had prevented the propeller piston from driving the blades to the fully feathered position.

It was determined that the aircraft had been operated within its normal weight-and-balance range throughout the accident flight

The fuel system of the Shrike Commander consisted of five interconnected tanks, with one fuel quantity indicator receiving an electrical signal from a float-type sensor mounted in the fuselage tank. The flight manual specified that a fuel quantity indicator was a mandatory instrument for operation of the aircraft.

A single fuel filler point was situated on the upper surface of the right wing, inboard of the engine, and connected to the right forward wing tank. It was not possible to assess the fuel quantity by "dipping" the fuel tank through the fuel filler point. After the aircraft had been recovered from the sea the fuel system was drained and found to contain approximately 0.75 L of aviation fuel and approximately 100 L of seawater. The fuel quantity indication system was examined. A wire that connected to the wiper arm in the fuel transmitter unit was found to be broken under its insulation, causing an intermittent open circuit, which resulted in a fluctuating fuel quantity indication. When the wire was repaired the fuel indication system operated normally. The wire to the wiper arm in the fuel quantity transmitter had been repaired on 7 August 1998 by resoldering the wire onto the wiper arm. The maintenance manual for the Shrike Commander provided instructions for removal and replacement of the transmitter unit; however, there were no instructions for disassembly and repair of any components within the unit. No other defect was found in the fuel quantity indication system.

A piece of adhesive paper was found covering the fuel quantity indicator. The pilot reported that he had covered the indicator before the flight because he noticed that its indications had been intermittent on a flight the previous day, and believed that the fluctuating indications might have alarmed the passengers.

Fuel planning and consumption

Company operations in the Torres Strait involved transporting passengers and freight on flights between the islands. Pilots would frequently undertake two or three flights each day, with up to five sectors per flight. The Shrike Commander was normally flown with less than full fuel tanks in order to permit greater payloads.

An examination of the aircraft fuel records since the fuel tanks were last filled on 13 October 1998 revealed that the average fuel consumption rate was 143 L/h, with an average sector time of 22 minutes. The company operations manual specified the procedure to be used for fuel planning. That procedure stipulated that the fuel consumption rate for the Aero Commander was to be calculated at a rate of 110 L/h, with an additional allowance of 20 L for each takeoff. The fuel log found in the aircraft revealed that, in practice, pilots had used a consumption rate of 120 L/h without any additional allowance for takeoff's.

A fuel log was maintained for each flight; however, during the investigation significant inconsistencies in the recording of fuel quantities were repeatedly found between consecutive fuel log records. The fuel log indicated that before the aircraft was partially refuelled prior to the accident flight, the fuel tanks appeared to have 170 L of fuel remaining. Investigation revealed that the actual quantity was substantially less.

Survival aspects

During the impact sequence, the passenger in the rear left seat was thrown over the centre seats into the front right seat, which was unoccupied at the time. The passenger in the centre right seat received a back injury. Both windscreens were shattered by the impact. The pilot pushed out the remaining pieces of perspex on the left windshield with his hands, cutting his finger in the process, and the passenger who had been thrown into the front right seat was able to kick out the remaining perspex pieces of the right windshield. The pilot and the three passengers in the front of the cabin exited the aircraft through the open windshields. The passenger in the rear right seat escaped through the emergency exit window. The cabin rapidly filled with water. All the occupants then swam ashore, assisting the injured passenger.

All the aircraft seating and seat-belt assemblies were found to be securely attached to the airframe. Surface corrosion was present on seat-belt end fittings, which was consistent with salt-water immersion, and all except one operated normally. The left rear passenger lap-belt end fittings were stiff to operate, and difficult to close properly. The end fittings could be easily placed together incorrectly, allowing improper locking of the assembly.

The aircraft was not equipped with life jackets, nor was that a requirement for the intended operation.

Organisational and management information

The company had expanded rapidly over a short period. At the time of the accident, it was operating 13 aircraft of various types. The company structure consisted of a managing director who was based in Melbourne, an operations manager who controlled sales and the allocation of tasks to aircraft, a chief pilot who managed the aircrew and assigned their duties, and a total of seven pilots. The chief pilot had worked for the company for six weeks, and was his first appointment as a chief pilot. During the course of the investigation, it became apparent that he had had minimal experience or guidance in the management of operational personnel. There was evidence that the new chief pilot had experienced difficulty in establishing practices that ensured compliance with safety requirements.

The pilot had been approved as a chief pilot in accordance with the procedures contained in the Civil Aviation Safety Authority (CASA) Air Operator Certification Manual. The guidelines in appendix 16 stated that it was preferable to have a chief pilot who could "manage the system" rather than one with the best manipulative skill. A candidate for the position of chief pilot was required to demonstrate to a CASA Flying Operations Inspector (FOI) an ability to operate within the regulatory framework. The checklist for the approval process contained a list of regulatory knowledge required of a chief pilot, however, no guidance was provided to an FOI in assessing the overall capability of an applicant to manage the objectives of the operator, within the boundaries imposed by aviation safety legislation.

No formal system of responsibility for maintenance control existed within the organisation. Unscheduled maintenance was recorded on a whiteboard in the operations room, but responsibility to ensure that the whiteboard was kept up to date was not a delegated duty of any of the company personnel.

Pilots verbally reported defects to the chief pilot, who would then approach the relevant maintenance organisation to arrange for rectification. The company used four different suppliers of third-party maintenance, depending on the aircraft. The remoteness of the location meant delays would frequently occur while spare parts were sourced.

The Lockheed "Tristar" was cleared to depart from Melbourne on a runway 16 RADAR FOUR standard instrument departure (SID). Following departure, the pilot turned right onto a heading of 300 degrees at the upwind end of the runway. The SID required the crew to maintain the aircraft on a heading of 160 degrees until 4NM from the airport, before taking up its assigned heading. There was no breakdown in separation standards.

There have been a significant number of similar occurrences involving this particular SID. Airservices Australia are presently discussing the layout of the relevant operational charts with Jeppesen, in order to reduce the potential for misinterpretation of the charts.

A Metro 23 aircraft was conducting Global Positioning System (GPS) approaches to runway 18 at Avalon. Whilst in the holding pattern north of the aerodrome the crew heard a radio broadcast from a Cessna 150 taxiing at Avalon. On leaving the holding pattern, the crew made a broadcast on the Avalon mandatory broadcast zone (MBZ) frequency advising their intentions. There was no response from any other traffic. At 5 NM on final approach to runway 18, the crew made a broadcast advising their intention to conduct a missed approach over the runway 18 threshold. Again, there was no response from any other traffic.

Overhead the threshold, at a height of about 500 ft, the crew heard a broadcast from Avalon Flying Operations (UNICOM) to the pilot of a Cessna, advising that there was a Metro inbound to his right. The Cessna had just become airborne from a grass strip, tracking to the west. The Metro crew sighted the Cessna and had to make a hard right turn and climb to avoid the aircraft.

The Cessna was being operated by a flying training organisation based at Avalon and had departed from an east-west grass strip located to the east of the runway 18 threshold. The grass strip is one of series of strips that were prepared and used by a previous manufacturer based at Avalon; however, none of the strips were depicted on any of the relevant aerodrome charts.

The Metro crew advised that they were not aware of any grass strips at Avalon. Accordingly, the Metro crew may not have associated any broadcasts that included reference to runway 27 as being applicable to Avalon.

The pilot of the Cessna advised that he made taxiing, entering and backtracking, and departure reports but did not get a response, nor did he hear any broadcasts from the Metro. He did, however, receive and respond to a broadcast from the Metro crew while in flight after the incident. Although the Metro crew heard the taxiing call, a number of hangars in the area may have masked radio reception by both aircraft when the Cessna was operating in the area of the grass strips.

The crew of an Airbus A320, operating under instrument flight rules (IFR), was cleared to descend to 4,000 ft on a BROOK TWO standard arrival route. The approach radar controller advised the A320 crew of two other aircraft, operating outside controlled airspace, on the reciprocal track to their aircraft. The controller reported a primary radar return only on the first aircraft and that the second aircraft was indicating an unverified Mode C altitude of 3,500 ft. The lower limit of controlled airspace in the area was 3,500 ft and was available for use by aircraft outside controlled airspace.

The pilot of the A320 levelled the aircraft at 4,300 ft and maintained that altitude until both pilots sighted the first aircraft. The A320 crew then received a Traffic Alert and Collision Avoidance System (TCAS) traffic advisory alert on the second aircraft. The TCAS indicated that the second aircraft was 800 ft below the A320. The crew then sighted that aircraft.

The minimum vertical separation requirement between an IFR aircraft in controlled airspace, and an aircraft operating under visual flight rules outside controlled airspace is 500ft. This spacing may on occasions be insufficient to prevent activation of a TCAS alert, or to provide adequate wake turbulence separation between aircraft.

A Boeing 747 (B747) was en route from Auckland to Melbourne, maintaining flight level (FL) 330. The aircraft was experiencing some turbulence. The crew were communicating with Auckland air traffic control via controller pilot data link communications (CPDLC) and were awaiting a response to a request to climb to FL350.

The crew had observed on their traffic alerting and collision avoidance system (TCAS) that another aircraft was crossing their route from the south-east to the north-west at FL350. They were aware that a clearance to climb to FL350 would not be available until that aircraft had passed. The other aircraft was a B737 en route from Wellington to Brisbane. The air routes intersected at the VIMAV reporting point. At 2002 the B737 crew reported at VIMAV maintaining FL350. At 2005, the B747 passed VIMAV.

At about 2010, the B747 crew received a conditional clearance to climb to FL350 at 2018. The delay in the climb approval was required to establish a 15-minute time standard between the two aircraft at the intersection of the air routes. The B747 crew immediately commenced climb to FL350 after the message was received. At 2012 they dispatched a message reporting they were maintaining FL350. When air traffic control notified the crew via high-frequency radio that they had not complied with the clearance, the crew descended the B747 to FL330. The B747 TCAS did not register an alert during the period that separation was infringed.

Normal company CPDLC practice for the B747 crew was for the non-flying pilot to read out the message on the screen, and for this to be confirmed by the flying pilot. Once the message and the subsequent response were confirmed by the two crew members the non-flying pilot dispatched the message to air traffic control.

The investigation found that the crew, for reasons unknown, had mis-interpreted the datalink message as an immediate clearance to climb. It is possible that, due to the turbulence being experienced, the crew acted hastily to acknowledge the message and climb the aircraft to reduce passenger discomfort. It is likely that either one or both of the crew were not as vigilant in their checking of the message as they would have been under less demanding circumstances.

A Boeing 747 (B747) was on an international flight from Sydney to Los Angeles, maintaining flight level (FL) 290. The flight was operating in controlled airspace and was being managed by the Brisbane Sector 8 air traffic controller, using procedural control methods. The flight crew and controller were communicating via controller-pilot data link communications (CPDLC). The crew requested approval to climb to and operate between FL290 and FL330. The controller sent an approval at 0659 on the CPDLC for the crew to climb to the block level. Prior to changing levels, the crew received traffic information on their aircraft traffic alerting and collision avoidance system (TCAS) display. The traffic was approaching from the opposite direction, 2,000 ft above the B747. The B747 crew maintained their aircraft at FL290 and immediately reported via the CPDLC that they were unable to comply due to traffic. This message was sent at 0659 but was not received at the controller's terminal until 0706. The delay was believed to be due to network lag. The traffic was subsequently identified as a British Aerospace 146 (BAe 146), en route from Norfolk Island to Sydney at FL310.

The controller had assumed responsibility for the sector following a handover/takeover a few minutes after the request from the B747 crew, to operate in the block level, had been received. The previous sector controller had coordinated the use of the block level with adjacent sectors in anticipation of approving the request, after establishing that the two aircraft had passed each other. Neither controller had calculated an estimated time of passing (ETP) for the aircraft. An ETP of 0659 was subsequently calculated after the occurrence. Air traffic control standards require that aircraft travelling in the opposite direction on the same route cannot climb or descend through the level of the other aircraft during a specific period before and after the ETP. In this case, the appropriate time standard was 10 minutes. Consequently, the controller should only have approved the use of the block level after 0709.

The controller taking over responsibility for the sector stated that he was aware of the confliction and had prepared the message approving the use of the block level, with the intention of holding it in the CPDLC terminal until after the aircraft had passed each other. The CPDLC did not have a hold function in the "reply" mode in which it was operating. Consequently, the message was ready for dispatch. The "send" function on the terminal was actioned by selecting an icon and activating this via a computer "mouse" button. The controller's response to the initial request should have been either to acknowledge receipt with "standby" or "request deferred". This would have then enabled the controller to respond further to the message after establishing a passing standard. The controller awaited an audio response from the terminal to indicate that the message was being held. When this did not occur, he prepared and sent a message to the crew instructing them to maintain FL290. The crew responded to this instruction with "Wilco". This response was received at the controller's terminal at 0701. The controller could have also used Flight Service high frequency (HF) radio communications as an alternative to the CPDLC, in order to instruct the crew to maintain FL290. Delays of up to 5 minutes were common when using the data link system.