Loss of separation

At 1305 Eastern Daylight-saving Time on 1 February 2011, a breakdown of separation occurred 22 km south of Williamtown (Newcastle Airport), New South Wales between a Boeing B737-7Q8 (737), registered VH-VBK, and an Israel Aircraft Industries Ltd Westwind 1124 (WW24) aircraft, registered VH-AJG. Both aircraft were in communication with and under the jurisdiction of Department of Defence (DoD) air traffic controllers based at Williamtown.

Separation between the aircraft reduced to 0.7 NM (1.3 km) on radar and 400 ft vertically when the required separation standard was 3 NM (5.6 km) or 1,000 ft. The vertical separation achieved was as a result of the 737 flight crew responding in accordance with a resolution advisory provided by their aircraft's traffic alert and collision avoidance system.

The investigation identified a series of errors by the Williamtown Approach controllers involving separation assurance, coordination and communication, and compromised separation recovery.

The investigation also identified three safety issues. The DoD advised that they reviewed and amended Williamtown procedures, introduced compromised separation recovery techniques training and trialled use of the conflict alerting function in the Australian Defence Air Traffic System at Williamtown.

On 31 January 2011, an Airbus A320-232 aircraft, registered VH-VQN (VQN), was taxiing for runway 29 at Darwin Airport, Northern Territory on a scheduled passenger service to Sydney, New South Wales.

The crew required a clearance to cross runway 11/29 in order to access the main taxiway for runway 29. On reaching the runway holding point, the crew received a clearance from air traffic control to cross the runway.  Prior to crossing, the crew checked the runway and approach paths for traffic. The pilot in command (PIC) stated that they were clear to the left, but the copilot noted that there was an aircraft lined up and stopped on runway 11. Soon after, the copilot observed the aircraft commence its take-off roll. He advised the PIC, who immediately stopped the aircraft. VQN had taxied past the holding point, but was short of the runway, resulting in a runway incursion.

Shortly after, they observed a Cessna 404 aircraft, registered VH-UOP (UOP), on a scheduled passenger service from Darwin to Snake Bay, Northern Territory take off on runway 11. A breakdown of runway separation occurred.

Air traffic control had provided the instruction for VQN to cross the runway based on the expectation that UOP would have commenced the take-off soon after receiving a take-off clearance.

Runway incursions are recognised as an ongoing safety concern for the aviation industry and have been cited in numerous accidents world-wide. This incident emphasises the need for controllers to remain vigilant in monitoring and scanning the runway and highlights the significance of pilots conducting a thorough visual inspection of the runway and approach paths prior to entering or crossing any runway, even if a clearance from air traffic control has been provided.

VH-TBR had been cleared to track via air route T9 from overhead Mount Hope, South Australia to overhead Narembeen, Western Australia. The aircraft had been cruising at Flight Level(FL) 350 but shortly before the incident the pilot had requested a descent to cruise at FL 290. The aircraft was recleared to decend to and cruise at FL 290 by Perth Air Traffic Control. A short time later, the Perth controller observed a radar return, from VH-TBR, on the edge of his screen. The return indicated that the aircraft was about 54 kilometres south of the cleared track and heading in a northerly direction. The controller immediately altered the course of an eastbound Boeing 727 aircraft to ensure separation between the two aircraft. It was established that the two aircraft came within 16 kilometres of each other, but at that time they were vertically separated by 2000 feet. However, during the descent made by VH-TBR, it had passed through the level of the other aircraft when both aircraft were estimated to be about horizontally separated by 32 kilometres. At this time the separation between the two aircraft did not comply with the prescribed standards. The investigation revealed that while the VH-TBR was enroute, and having just climbed to cruise at FL 350, the aircraft captain disengaged the autopilot to retrim the aircraft for level flight. When the autopilot was then re-engaged, the normal sequence was interrupted and subsequently not completed. As a result the autopilot was not re-coupled to the Inertial Navigation System(INS). This resulted in the aircraft maintaining a constant heading and under the influence of a changing wind velocity and the absence of normal enroute heading changes the aircraft diverted from the cleared track.

Both aircraft were tracking towards radio navigation aids at Biboohra from approximately opposite directions, and were the only aircraft using those tracks. VH-PCO's climb had initially been restricted to 4500 feet, to maintain separation with VH-TAK on descent. The controller responsible for separating the two aircraft became preoccupied with other traffic, and, overlooking the separation requirement, cleared VH-PCO to climb to 8000 feet and VH-TAK to descend to 6000 feet. VH-PCO had reached 8000 feet, VH-TAK had reached 7000 feet, and the two aircraft had passed before the mistake was realised. A breakdown in vertical separation standards had occurred in the vicinity of the radio navigation aids. However, the proximity of the two aircraft to one another at the time of passing was not established. The Cairns controller responsible for separating the two aircraft was performing an established traffic management function, which combines the dual responsibilities of Aerodrome and Approach control utilising a single radio communication frequency. This controller's workload at the time of the incident was subsequently assessed as being moderately high. Following this incident, emphasis was made on the requirement for air traffic control staff to process traffic within the limitations of the present air traffic control system, and in accordance with published standards and procedures. Additional traffic management procedures have also been instituted at Cairns, providing increased regulation of departing and arriving traffic. Other arrangements at Cairns are also being reviewed with the intention of making changes if appropriate. Matters under review include: the general management of airspace in the Cairns area; control tower management and staffing; and the adequacy of existing facilities.

The pilot of VH-CJR was conducting a flight from Prosperpine to Gladstone via Rockhampton. After passing over Charon Point he decided to track to the west of his planned track and overfly Marlborough enroute to Rockhampton and thus remain well clear of the restricted area to the east. The pilot did not advise Rockhampton Air Traffic Control of his revised tracking details. When the aircraft was 36 kilometres north-west of Rockhampton, the pilot contacted Rockhampton Tower and requested a clearance to cross the Rockhampton Contol Zone. The tower controller cleared the aircraft to track to Rockhampton remaining at least two kilometres to the east of the Rockhampton to Marlborough railway line, at an altitude of two thousand feet. The controller did not advise the pilot that the clearance was an amendment to his planned tracking details, as is required. However, the pilot acknowledged the clearance without query. This clearance was given to VH-CJR to provide lateral separation with VH-TJJ, which was about to depart Rockhampton. The pilot of VH-TJJ subsequently reported that the aircraft had departed and passed through 3000 feet. Some two and a half minutes later the pilot of VH-CJR reported the position of the aircraft as five kilometres north-west of Rockhampton at 2000 feet. Neither pilot reported sighting the other aircraft. The pilot of VH-CJR, who was inexperienced in the Rockhampton area, did not comply with the terms of his clearance.

The southbound aircraft, BA 11, was cruising at FL330. The northbound aircraft, MH 24, had been cleared to climb to and cruise at Flight Level(FL) 350, with a requirement to reach the assigned level by 1801 hours local. Shortly afterwards BA 11 requested a diversion to the right of track. The aircraft was cleared to divert up to 90 kilometres to the right of track. The tracks flown by the aircraft were laterally separated by approximately 80 kilometres. About five minutes after being given approval to divert from his cleared track, the pilot of BA 11 requested a clearance to climb to FL 350. This request was denied by the Perth controller and the aircraft was given approval to divert either to the left or right of track, as required. At 1811 hours local the Perth controller gave BA 11 a clearance to climb to FL 350, at 1816 hours local. The aircraft acknowledged the clearance and during the subsequent climb advised sighting another aircraft, MH 24, an estimated two kilometres to the right and 1400 feet above his level. The investigation determined that the Perth controller had mistaken the time MH 24 had been required to reach FL350, 1801 hours, for the time he had calculated that the aircraft would pass. He had thus applied the required separation standard to this time instead of the calculated time of passing of 1818 hours local.

Circumstances:

The two aircraft were on identical tracks, with the slower aircraft (VH-ITF) in front and maintaining 8000 feet. VH MWX was faster and maintaining 10000 feet. Due to military flying activity, they were unable to fly from Ballidu direct to Perth but obtained a clearance to track via Clackline. VH-ITF obtained a clearance to enter controlled airspace (65 nautical miles from Perth) at 6000 feet, while VH-MWX was cleared to enter at 5000 feet. Although both aircraft had reported at Ballidu at the same time, the pilots were unable to see the other aircraft. VH-ITF descended to 6000 feet and the pilot of VH-MWX elected to descend to 7000 feet until he could maintain visual contact with the other aircraft. If he had not seen the other aircraft before entering controlled airspace (CTA) he intended orbiting outside CTA until separation was obtained. The pilot of VH-MWX saw the other aircraft about 13 kilometres before the airspace boundary and commenced descent to 5000 feet. He was overtaking to the left of the other aircraft and at the same altitude when VH-ITF was instructed to make a left orbit by the controller. This action was halted when the pilot of VH-MWX advised the other pilot and the controller against the turn because his own aircraft was in the way. VH-MWX subsequently descended to 5000 feet and VH-ITF was instructed to orbit to gain lateral spacing with the other aircraft. Identification of VH-MWX on radar was completed at 57 nautical miles (103 kilometres) from Perth, after the pilot had reported at 5000 feet.

Significant Factors:

The following factor was considered relevant to the development of the incident:

1. The controller used a poor technique in allocating clearances. This incident was not the subject of an on-scene investigation.

No Summary

When the pilot of VH-MXL lodged his flight plan, relevant details were inadvertently not transmitted to all necessary recipients by the AFTN system. As a result, Melbourne Approach was unaware of the planned track of the aircraft. The flight evidently proceeded normally until the pilot had reported his position at Port Phillip Heads to Melbourne Flight Service, and had requested an airways clearance. Essendon aerodrome was closed to Visual Flight Rules operations, and Melbourne Approach, after receiving details from Flight Service, cleared the aircraft to enter controlled airspace at 4000 feet on track from Port Phillip Heads to Essendon. This clearance was passed to the aircraft 11 minutes after the initial request. The Approach controller had not been informed that the aircraft was tracking via Frankston, a track which crossed the NDB instrument letdown pattern for Moorabbin. Shortly afterwards the aircraft was identified on radar by the Approach controller, and it became evident that the aircraft was in conflict with VH-TKM, which was conducting an instrument approach to Moorabbin. The airways clearance for VH-MXL was cancelled, but before positive action could be taken the aircraft passed within about half a kilometre of each other. It was considered that a number of communication breakdowns contributed to this incident. (a) The flight plan was incorrectly addressed. (b) The relevant Flight Service officer did not inform Melbourne Approach of the tracking details of the aircraft. (c) The Flight Service officer did not query the clearance as issued, although he was aware of the tracking details. (d) The pilot did not query the clearance, although it would have been virtually impossible for him to comply with the tracking instructions from his present position.

Circumstances:

VH-HYF departed Adelaide Airport on an 'Adelaide East 2 Mildura' Standard Instrument Departure (SID), with an unrestricted climb to its cruising level of Flight Level (FL) 370, then via the 'Tango 77' route to Brisbane. Because a Boeing 747 from Melbourne would be overflying Mildura at FL 310, Melbourne had co-ordinated with Adelaide a requirement for VH-HYF to reach FL 330 by 37 km south-west of Mildura. VH-EAK was flying from Sydney to Adelaide via Mildura, cruising at FL 310. It was on the reciprocal heading to VH-HYF and appeared on the Adelaide Control radar display at 235 km from Adelaide. When VH-HYF was transferred to Adelaide Control, the controller requested that the aircraft maintain its best rate of climb to FL 330. His objective was to climb VH-HYF above VH-EAK, using radar to maintain separation instead of procedural control. This would allow VH-EAK to follow its preferred descent profile to Adelaide, and for VH-HYF not to be held at a lower level until procedurally separated with the overflying Boeing 747. Approaching FL 310, VH-HYF experienced an increase in ground speed due to a strong westerly windshear increasing the closing speed between the aircraft. While maintaining maximum rate of climb, the air speed of VH-HYF fell below the minimum manoeuvring speed. With the airspeed trend indicator fluctuating due to turbulence, the Captain reduced the climb angle to accelerate the aircraft without advising the controller of the reduction in climb performance. VH-HYF passed VH-EAK 200 km north-east of Adelaide, with 800 ft vertical and 0.4 nm horizontal separation with less than the required standard of 2000 ft vertical or 7 nm horizontal separation. VH-HYF had regained its normal rate of climb as the aircraft passed. The controller had been operating two sectors on combine, with a subsequent increase in co-ordination workload. He had monitored VH-HYF during its climb to FL 310, at which time it was 76 km to the west of VH-EAK. At its initial climb rate he expected VH-HYF should have passed FL 340 by the estimated time of passing. The controller continued his scan of the radar display. When his gaze returned to these aircraft, the noticed that the radar returns were merged, which would be normal as they passed. When the radar returns separated, the controller noted that the altitude indication for VH-HYF was showing the aircraft to be at FL 330. He therefore had no reason to believe that a breakdown in separation had occurred. A discussion had also been in progress during this period with other controllers regarding industrial matters. This situation was causing the controller considerable amount of anxiety and may have been a factor in this occurrence.

Significant Factors:

The following factors were considered relevant to the development of the incident

1. The controller applied inadequate separation standards so as not to cause inconvenience to the aircraft.

2. The controller expected that VH-HYF would maintain the same rate of climb to FL 330.

3. The controller was operating two positions on combine.

4. VH-HYF experienced windshear increasing the tailwind component and closing speed with VH-EAK.

5. In turbulent conditions the air speed of VH-HYF fell below its minimum manoeuvring speed. The Captain accelerated the aircraft, reducing its rate of climb without advising the Controller.

6. The controller's attention may have been affected by anxiety concerning industrial matters. This incident was not the subject of an on-scene investigation.