Loss of separation

A Boeing 747 had just landed on runway 19 and was in the process of vacating the runway. At the same time, a King Air aircraft was given a clearance to cross the runway at taxiway "M".

The pilot of a Beech 99 requested a take-off clearance from the intersection of runway 19 and taxiway A4. The ADC (aerodrome controller) assessed that both the B747 and King Air would be clear of the runway in time and issued a take-off clearance to the Beech 99. As that aircraft entered the runway, and commenced the take-off run, the crew observed the King Air about to cross the runway. They rejected the take off and queried the take-off clearance. The ADC saw no safety risk and recleared the aircraft for take off.

The ADC was probably surprised to a minor extent about the rolling take-off, however he judged that there were no safety implications in allowing the take off to continue. The distance between taxiway A4 and taxiway "M" was 1410 metres.

After take-off from runway 34L VH-CZB was tracking outbound from Sydney on a West Maitland One, Standard Instrument Departure (SID).  On this SID the aircraft was maintaining a track of 335 degrees outbound on the localiser at an altitude of 5,000 ft.  The crew were in contact with Sydney Departures Control.

VH-CZK was inbound on a Letti One Standard Arrival (STAR), heading 160 degrees, on a track that was close to the reciprocal of the track of VH-CZB.  The crew were in contact with Sydney Approach Control and were cleared to descend to 7,000 ft.

A third aircraft, VH-TCH, was also inbound and ahead of VH-CZK. Because VH-CZK was faster than VH-TCH and expected to overtake it, the approach controller obtained approval from the departures controller to turn VH-TCH left.  The purpose of this was to allow VH-CZK to get ahead of VH-TCH and also to allow it to descend through the level of VH-TCH.

Under existing procedures, the approach controller was not permitted to descend VH-CZK below 6,000 ft. However, when contacting VH-CZK, the controller inadvertently cleared VH-CZK to descend to 4,000 ft which was consistent with procedures previously in place. The crew acknowledged and commenced descent.

A short time later the crew of VH-CZK saw an approaching aircraft which was directly ahead and slightly below them. They queried the controller on whether they were cleared to 4,000 ft and were instructed to maintain 6,000 ft. They were then advised that the other aircraft, VH-CZB, was maintaining 5000 feet. The crew stopped the descent and climbed to 6,000 ft.

The radar recording showed that separation between these two aircraft had reduced to 1.1 NM horizontal and 600 ft vertical.

At Sydney there have been a number of ongoing changes affecting air traffic control. These include the introduction of a new Interim Radar Display System (IRDS), and a new parallel runway system requiring new procedures. STARs were recently introduced and sectors formally based at Sydney have been progressively transferred to Melbourne or Brisbane.

Because of noise complaints resulting from the new parallel runway system, aircraft at lower altitudes in the vicinity of the airport are now restricted to narrow corridors and are required to fly long approaches.  As a result, they remain under approach or departure control for a longer period than was the case, thus increasing controller workload.

To assist in minimising co-ordination between control positions a system of vertical airspace separation was introduced to assigned sections of the terminal area. In the section relevant to this occurrence the departures controller was able to assign altitudes up to 5,000 ft, without co-ordination and the approach controller could assign altitudes down to 6,000 ft, also without co-ordination.

The adjacent section of airspace outside the corridor was managed by departures control, which was the reason the approach controller co-ordinated with the departures controller to divert VH-TCH left of track. However, had the approach controller waited a short time, both VH-CZB and VH-CZK would have entered an area of airspace controlled by approach control and in which the approach controller could have arranged the separation and passing, without co-ordination. Due to the enforced long approach flight path there was ample time remaining for the approach controller to arrange separation and descend VH-CZK.

The workload at the time was moderate.

Significant Factor

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

The approach controller inadvertently reverted to procedures which were no longer in place.

The pilot of VH-JZU contacted Essendon Tower approaching Williamstown, requesting a clearance to enter the control zone on track to Essendon. The tower controller was unable to establish radio communication with VH-JZU and so no clearance was issued.

An IFR aircraft, VH-UJV, was on descent into Essendon and communicating with Melbourne Approach Control. The Essendon tower controller noticed an unidentified aircraft entering the control zone at West Gate, on track for Essendon. He advised the approach controller and the descent of VH-UJV was stopped at 2000 feet. VH-UJV was climbed back to 2500 feet.

The pilot of VH-JZU, which was the unidentified aircraft, continued to Essendon and on receiving a green light from the tower, landed. The pilot of VH-UJV was able to sight and follow VH-JZU. A loss of separation may have occurred, due to the unapproved entry into the zone by the pilot of VH-JZU.

The inexperienced pilot of VH-JZU later said he thought he had received a clearance, but in hindsight realised this was a mistake on his part. When he later tried to contact Essendon Tower, he could not do so but continued, thinking he had received a clearance.

Significant Factors

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

1. VHF radio communication equipment failure in VH-JZU.

2. Misunderstanding of communications by the pilot of VH-JZU.

VH-RMX was making touch-and-go landings at Avalon and was on the crosswind leg for runway 18 at an altitude of 1400 ft when the pilot reported a helicopter passing beneath him tracking in the opposite direction. Melbourne radar confirmed an aircraft squawking code 2100 half a mile inside the Avalon control zone tracking towards Geelong at 1100 ft.

The helicopter did not respond to calls and faded from radar 90 km southwest of Avalon.

On departure the pilot of VH-DXI requested climb to amended altitude 10,000. Due to another aircraft just ahead at 8000 feet the controller issued a clearance to climb to amended altitude 7000 feet. On climb the pilot's attention was diverted when a passenger spoke to him. The aircraft had climbed to almost 8000 feet when the controller queried the pilot on his altitude. The pilot apologised and descended back to 7000 feet. The longitudinal separation at the time was four miles, instead of the required five miles.

Significant Factor

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

1. The pilot inadvertently climbed the aircraft above the altitude he was cleared to.

The design of Area Alpha was negotiated between the gliding clubs and ATC. It was intended to provide suitable airspace to cater for the traffic density, and to meet the needs of the training syllabus for glider pilots. For example, the average 1,500 ft between ground level and the base of the 2,000 ft step is insufficient for spin recovery training which is mandatory for all glider pilots.

The gliding clubs have a record book adjacent to the telephone in the club house to record details of the release of the airspace and have an 'Alpha Open' sign at the launch point to advise pilots when release approval has been obtained from ATC.

During the launch of the three gliders the 'Alpha Open' launch point sign was displayed although no request for release had been made to ATC, and no approval had been given. The glider pilots were not aware that Area Alpha had not been released. ATC routed the B767 through the area in the belief that glider traffic was conforming to the area step restrictions. Weather conditions at the time were such that the gliders were able to climb to 4,000ft.

There was no indication in the record book adjacent to the club house telephone that any contact had been made with ATC, and ATC did not have any record of telephone calls received from the clubs.

The gliding clubs were not able to determine who had displayed the sign that day and were not sure that the sign had been removed after the previous day’s flying.

The B767 had been correctly routed through the area. The crew was alert to the high-density traffic and was maintaining a heightened visual scan during the descent into Avalon.

Significant factors

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

1. The 'Area Open' sign was displayed when an ATC clearance was not available.
2. ATC was not aware that the gliders were operating in controlled airspace.

SAFETY ACTION

During the investigation, Airservices Australia revealed that as part of the implementation of the ICAO Airspace structure on 20 June 1996, the upper limit of the airspace available for gliding OCTA ('G' airspace) will be 3,500 ft over Bacchus Marsh and 4,500 ft to the west of Bacchus Marsh.

The following safety actions have also been taken.

The gliding clubs have:

1. alerted all glider pilots operating at Bacchus Marsh to the circumstances of this incident;
2. tightened up the mandatory recording of telephone requests for the release of Area Alpha airspace;
3. manufactured a sandwich board indicator of 'Area Open' that shows the date, the name of the person who obtained the clearance and any conditions attached to the clearance;
4. required that the sandwich board be placed in the club house adjacent to the telephone at the completion of each days flying; and
5. required that during the first launch after the sandwich board is placed at the launch point the tug pilot is to call ATC to confirm that Area Alpha is open.

Approval was given to Melbourne Sector 12 by Sydney ATC for the Nomad to climb clear of the Sydney 230 radial for parachute dropping from FL125. At about the same time, an Airbus was inbound to Sydney from Melbourne via a Rivet STAR. As the Airbus was passing FL130 on descent, the Nomad was observed on radar by Sydney Arrivals, near the inbound track climbing through FL110, in potential conflict with the descending Airbus.

The Arrivals Controller contacted Melbourne Sector 12 who confirmed that they would be separating the two aircraft. Although this was accepted, a short time later the aircraft were observed to pass within 4 NM of each other at the same level, when the minimum lateral separation required was 5 NM.

A subsequent investigation did not reveal any reason for the lack of positive control by Melbourne Sector 12. The incident was also the subject of a separate ATS Quality Assurance investigation.

Three aircraft were in the landing sequence for runway 34R at Sydney. VH-NEK, on right downwind as number three, was given an ATC instruction to "sight and follow" the second aircraft, VH-DMO, which was on a left circuit. However, VH-NEK was seen to follow VH-SMH, the first aircraft in the sequence which was also on a right circuit. Separation was lost between VH-NEK and VH-DMO before the Approach Controller could contact the pilot of VH-NEK, who had already changed to Tower frequency before being instructed to do so. As a result, the aircraft came within 1 NM of each other before VH-NEK was vectored to follow VH-DMO.

Subsequent investigation indicated that VH-DMO, would have been in the "two o'clock" position from VH-NEK, at a range of about 10 NM, when the pilot of VH-NEK was instructed to follow the second aircraft. The first aircraft in the sequence, VH-SMH, would also have been at "two o'clock" from VH-NEK, but at a range of only 5 NM. VH-DMO was also nearly head on to VH-NEK at the time and would have been difficult to see. As a result, the pilot of VH-NEK mistook VH-SMH for the second aircraft and turned inside VH-DMO, resulting in a loss of separation. In hindsight, the "sight and follow" instruction may not have been the most suitable for this particular situation.

The F27 was tracking from Canberra direct to Bindook VOR on climb to FL170. At about the same time, a military PC-9 was tracking from Shelleys NDB to Richmond via Bindook VOR, also at FL170.

Both aircraft had just been handed over to Sydney Arrivals by Melbourne Sector Control, with the aircraft on converging tracks at the same level.

The Arrivals Controller experienced problems with the transponder code of the PC-9 and, while attempting to correct the display errors, realised that radar separation would not be maintained. Instructions were given to the PC-9 to change heading, and for the F27 to descend to FL160. However, before the aircraft could respond, the minimum separation standards were infringed.

VH-LIH was tracking out of Albury for Sydney and was cleared to climb to flight level 120. VH-FNE was inbound for Albury, from Sydney, initially maintaining flight level 230. Because one of the radar stations was out of service the radar coverage in that area was unreliable and procedural separation was employed. The crew of VH-FNE were given descent to flight level 120, in error. The air traffic controller had intended to descend VH-FNE to flight level 130.

The crew of VH-LIH requested a clearance to climb to a higher level. This was not allowed as the controller mistakenly believed that VH-FNE was at flight level 130. The controller gave both crews traffic information on each other and asked them to report sighting and passing each other. In response the crew of VH-FNE told the controller they had been cleared to flight level 120, were currently at flight level 126 and were climbing back to flight level 130. Following discovery of the error in giving VH-FNE flight level 120, this aircraft was maintained at flight level 130 until it had passed VH-LIH.

Significant Factor

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

1. Incorrect level clearance issued by the air traffic controller.