Loss of separation

A Rockhampton City Council airport vehicle had been cleared by the Aerodrome Controller (ADC) to enter all movement areas for a runway inspection. This clearance enabled the driver to enter any runway without obtaining further clearance. Subsequently, a Fokker F28 VH-EWA was cleared to land on runway 15. When the aircraft was on short final the pilot noticed a vehicle on the runway approximately 1400 metres from the runway threshold. The pilot commenced a go-round and the ADC instructed the vehicle to vacate the runway immediately. The vehicle then cleared the runway, and the F28 made a normal circuit and landing.

The ADC stated that he had inserted the "runway occupied" strip into the active display board as is normal procedure when runway inspections are in progress. When the F28 turned base he scanned the runway, and as he did not sight the vehicle on the active runway he cleared the F28 to land. When the aircraft was on short final, another scan of the runway revealed that the vehicle had moved into view from behind two obstructions, a window mullion in the tower and a concrete light tower on the edge of the apron. The lighting tower is some distance from the tower cab and requires considerable physical displacement by the controller to effectively see behind it. Local procedures have been changed as a result of this occurrence. Vehicles on the movement area are now required to obtain a specific clearance before entering a runway.

Relevant Factors

1. The vehicle was not required to obtain specific clearance to enter the runway and entered the runway without the controller noticing.

2. The vehicle stopped on the runway in a position which was obscured by obstructions.

3. The controller failed to adequately scan the full length of the active runway before clearing the F28 to land.

Factual information

VH-MZI departed Albury at 1634 EST on a flight to Canberra. The aircraft was maintaining 9,000ft and the pilot contacted Canberra approach control (APP) prior to the control area (CTA) boundary for an airways clearance, advising that he was on the 238 degree radial of the Canberra VOR. This was north of the nominated track (the 234 degree radial) and was due to conflicting traffic outside controlled airspace. The fact that VH-MZI had reported north of the nominated track was not assimilated by the approach controller.

Canberra Approach and Departures control were being operated in the combined mode at the time of the incident due to the low volume of air traffic. The controller performing both functions was positioned at the approach console and had set the approach radar display on the 40 NM range and the departure control console radar display on the 80 NM range. He issued an airways clearance for VH-MZI to enter control area on track direct to Canberra at 9,000ft and identified the aircraft on the radar display at approximately 50-55 NM from Canberra. This identification was made on the departure control radar but, with the 80 NM range selected, the display did not readily indicate that VH-MZI was offset four degrees from the nominal track.

VH-ARQ departed Canberra for Albury at 1656 and had been processed by APP to intercept the flight planned route (234 radial) on climb to 8,000ft.

At 1704, the pilot of VH-MZI requested descent for his arrival at Canberra and was cleared to descend to 4,000ft, maintaining terrain clearance by visual reference to the ground. At the same time, the controller issued VH-MZI a radar vector right to heading 090 degrees with the intent of ensuring radar separation between VH-MZI and VH-ARQ. The controller had still not noticed that VH-MZI was north of the nominal track. Consequently, the vector on to heading 090 turned that aircraft across the flight path of VH-ARQ instead of resolving the 'nose to nose' confliction.

At 1704.40 the pilot of VH-ARQ reported level at 8,000ft. At approximately 1705, the controller checked his 40NM range radar screen and realised that the radar separation between VH-MZI and VH-ARQ was nearing the minimum of 5 NM.

At 1705.50, in response to a request from the approach controller, the pilot of VH-MZI reported his altitude as 8,300 ft. Seven seconds later, the approach controller asked the pilot of VH-ARQ to sight VH-MZI passing five miles ahead of him. The pilot reported that he had the other aircraft in sight and later said that he thought the distance was nearer to two miles than five. The pilot of VH-MZI also sighted VH-ARQ at approximately the same time and also thought the distance to be approximately two miles.  Both pilots commenced avoiding action at this time by turning right.

Radar analysis showed that the aircraft passed within 800m at the same level and with a closing speed in excess of 300 knots. This occurred at 1706.16, eight seconds after the controller had initiated the request for the pilot to maintain his own separation. The required separation standard was 5 NM horizontally by radar, or 1,000ft vertically. An instruction to a pilot to sight traffic and maintain separation visually is a valid option for a controller but it must be exercised in sufficient time to enable the pilot to position his aircraft relative to the traffic.

Controllers on duty at the time of the occurrence considered the radar display to be of poor quality. They stated that it was "blurry", "fuzzy” and "swimming" during the period surrounding the occurrence. The display was suitable for separation purposes but did not allow ready differentiation between an aircraft on-track and an aircraft a few degrees off-track.

Significant factors

1. The radar display was such that small track deviations were not readily discernible on the 80 NM range scale.
2. The approach/departures controller did not assimilate the fact that the pilot of VH-MZI reported on the 238 degree radial of the Canberra VOR in lieu of the expected track of the 234 degree radial.
3. The radar vector given to VH-MZI turned that aircraft across the flight path of the other aircraft.

The pilot of VH-OWK was on a solo navigation training flight. A clearance was requested from Wagga Tower to enter the Wagga control area step. Due to other traffic the pilot was told to remain outside the control area and to expect a delay.

Subsequently the pilot gave a position report that showed the aircraft was in the control area and conflicting with an F27 aircraft, VH-FNC. Instructions were given to the pilot to make a 180 degree turn and radar separation was established. The pilot then elected to return to Canberra without completing the planned flight.

Significant Factors

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

1 Pilot of VH-OWK inexperienced.

2 Poor navigation, by pilot of VH-OWK.

VH-WMJ was tracking from 18 miles south-east of Wagga direct to Young, descending from 8000 ft to 7000 ft. A RAAF DC3, Tester 922, was tracking from over Wee Jasper to over Wagga at 8000 ft. The crew of Tester 922 called Wagga Tower at 33 miles requesting clearance to enter the control area. This position was 2 miles inside the control area and a clearance to enter had not been previously requested or given.

Although the aircraft were well clear of each other the separation standards were infringed.

Significant factors

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

1. The crew of Tester 922 did not follow required procedures and obtain a clearance prior to entry into controlled airspace.

VH-EWF was on a visual approach to Melbourne runway 34, tracking via the Essendon runway 26 localiser for a right base. VH-HCY took off from runway 34 at Melbourne and was cleared to make a left turn to track across the airfield on a south-easterly heading, to remain east of the runway 34 centreline for a left base for runway 35 at Essendon. VH-HCY had been cleared to maintain 1500 feet.

The Melbourne Aerodrome Controller (ADC) intended that VH-HCY pass behind VH-EWF and that he would provide visual separation. When VH-HCY was over the airfield, the ADC momentarily diverted his attention to the radar screen. When he looked back to check the position of VH-HCY he was unable to see the aircraft. As VH-HCY had already been transferred to Essendon Tower frequency, the Melbourne ADC asked the Essendon ADC if he could provide visual separation. The response was that he could not. The Melbourne ADC then instructed VH-EWF to climb immediately to 2000 feet. Separation between the two aircraft reduced to less than the minimum required. When the confliction was resolved VH-EWF was cleared to continue the visual approach.

The pilot of VH-HCY said that he had VH-EWF in sight from when it was east of Essendon and was watching the situation closely. The Melbourne ADC had not given traffic information to either aircraft on the other on the basis that he was providing visual separation. When he instructed VH-EWF to climb to 2000 feet he advised that the climb was due to conflicting traffic.

There were other options available to the ADC for the processing of these two aircraft, but these were not adequately considered at the time. Hazy conditions existed on the day of this incident.

Factors

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

1. The option chosen for tracking VH-HCY was a poor option in that it put the aircraft into airspace that created a potential conflict with VH-EWF.

2. Having tracked VH-HCY in the manner chosen, the ADC then inappropriately relied on visual separation between the two aircraft on converging headings in hazy conditions.

3. The ADC did not maintain vertical separation by restricting VH-EWF's descent to 2500 feet in a situation where radar and visual separation were reducing in hazy conditions.

4. The ADC did not recognise the deteriorating situation and initiate alternative action until it was too late to prevent the loss of separation.

VH-TEQ was conducting circuits and was instructed to report when ready to turn base for runway 12. VH-TAK was on approach for runway 35.

The aerodrome controller (ADC) was under training and when the pilot of VH-TEQ reported ready for base he elected to make that aircraft number one in the landing sequence. He instructed VH-TEQ to make a short approach and then cleared that aircraft for a touch-and-go with a request to expedite crossing the runway intersection. The pilot of VH-TEQ attempted to carry out these instructions to the best of his ability but did not perform as speedily as the ADC expected.

The rated controller observed this action and decided that the runway separation standard would exist by the time VH-TAK needed a landing clearance.

The crew of VH-TAK were twice told by the ADC to expect a late landing clearance and the captain elected to continue his approach as he could see that the runway was clear and air traffic control had given him a landing expectancy. Although realising that another aircraft was on a crossing runway and conducting a lookout, the crew of VH-TAK did not see VH-TEQ until after touch down. Traffic information was not passed to either crew.

When the ADC trainee and training officer realised that the runway separation standard may be infringed, they considered that the safest action was to land VH-TAK as VH-TEQ had commenced rotation from the touch-and-go. A landing clearance was issued to VH-TAK as that aircraft approached the threshold. When VH-TAK was on its landing roll, VH-TEQ crossed the runway intersection at a height of approximately 100-150 ft. As a result, the required landing separation had not been maintained.

Significant Factor

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

1. The ADC trainee misjudged the traffic situation.

2.The ADC training officer did not take sufficient action early enough to prevent a breakdown in separation standards.

3.Traffic information was not given to either crew.

While enroute between Corryong and Bathurst, the pilot of VH-ICS called Canberra Approach and requested a clearance to enter Canberra controlled airspace. An attempt was made by air traffic control to identify the aircraft but due to poor radar coverage, in the area and the aircraft's altitude, this could not be achieved. In response the pilot was instructed to remain outside controlled airspace.

Subsequently a brief radar return from VH-ICS was observed in the Wagga controlled airspace, about 20NM west of the planned track of the aircraft. There was inadequate radar contact to allow radar separation standards to be applied. The aircraft track conflicted with that of VH-AWW which was tracking in the opposite direction.

The pilot of VH-ICS said, that in hindsight, he should have planned a route that had more navigational aids to assist with track maintenance. He was tracking on a back bearing from the Corryong NDB and was unable to obtain a distance from the Canberra international DME. Hence, he was unable to accurately determine his position and ascertain that he was off the planned track.

Significant Factors

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

1. The route planning by the pilot was poor.

2. The aircraft was not equipped with a domestic DME.

3. The enroute track maintenance by the pilot was inadequate.

VH-UZP departed Townsville on the Townsville-Collinsville track but was then cleared to track direct to Mackay. VH-JJY, a faster aircraft, departed Townsville six minutes later and climbed initially on the Townsville-Bowen track before also being given a direct track to Mackay. The aircraft were thus on converging tracks.

VH-JJY was subsequently cleared to divert up to 10 NM right of track to avoid thunderstorm cells. This brought the aircraft into potential conflict with VH-UZP, so the controller instituted a stepped climb procedure between the two aircraft. He then noted that VH-JJY was not diverting far off track so he cleared that aircraft to climb through the level of VH-UZP which by this time was level at FL210. The controller instructed VH-JJY to expedite climb to FL 220. However, VH-JJY then diverted further right of track (but still within 10 NM of track) and did not climb at the rate the controller expected. This resulted in a breakdown of separation standards between the aircraft. Recorded radar data indicated that when the aircraft were 3 NM apart, there was 200 ft vertical separation. The prescribed standard is 5 NM or 1,000 ft.

Neither crew was given traffic information on the other aircraft. The controller, on realising that separation standards could be infringed, gave the leading aircraft (VH-UZP) a heading change from 125 degrees to 140 degrees. This was not of sufficient magnitude to ensure that the separation would be maintained.

Significant Factors

The following factors are considered relevant to the development of this incident:

1. Weather avoidance considerations resulted in the aircraft diverting off track.

2. Appropriate separation standards were not applied following the diversion of VH-JJY off track.

Air traffic control (ATC) cleared the pilot of VH-EWF to descend to 5,000 ft and to divert left of the 144 VOR radial as required to avoid weather. However, the pilot subsequently diverted to the right of the 144 radial. A breakdown in separation standards occurred with VH-XFT, a scheduled passenger flight outbound from Rockhampton, on climb to 7,000 ft and tracking via the 116 VOR radial.

The pilot of VH-EWF had requested clearance to track 5 NM left of the 144 radial. He was advised by ATC that the clearest conditions were to the west of that radial. The pilot later advised that he had diverted 5 NM left (west) of track. However, he had subsequently diverted to the right of the 144 VOR radial, and at 15 NM from the aerodrome, the aircraft was established on the 125 VOR radial.

VH-EAN was en route from Sydney to Perth, cruising at flight level (FL)350. N99SC was en route from Essendon to Sydney cruising at FL410 and requiring descent. Both aircraft were under the control of the Melbourne Air Traffic Control Centre, Sector 7. It was apparent that the two aircraft would be in lateral conflict near Yass. The controller cleared N99SC to descend to FL360.

Above FL290, for aircraft that are not laterally separated, the minimum vertical separation is 2000 feet. In this instance the controller had only provided 1000 feet. The two aircraft passed with about three and one half miles lateral separation and 1000 feet vertical separation. For aircraft not vertically separated, the minimum lateral separation in this instance was five miles.

The controller realised his error but too late to rectify the situation. Investigation revealed that prior to the incident the controller had been busy with aircraft inbound to Sydney, entering the holding pattern at Bindook. All levels assigned to other aircraft had been in the range of FL210 to FL260 where only 1000 feet vertical separation is required. He believed it was this that had led him to inadvertently apply the same standard to VH-EAN and N99SC