On climb out of Brisbane the crew had problems with the No 2 engine bleed and at the cruising level of Flight Level 310 were unable to control the cabin pressurization. The aircraft descended rapidly to 10,000ft and returned to Brisbane. The problem was isolated to a failed duct. The aircraft was already operating on an MEL due to the No 1 airconditioning pack being unservicable. Therefore, with the failure of the No 2 pack, pressurization was unable to be maintained. The Company is assessing the need to limit departures with one airconditioning pack inoperative.

On two occasions the aircraft suffered a loss of power on take-off due to fuel starvation. The electric fuel pump was found to be inoperative and was replaced. Subsequent operations were normal.

The number 3 engine began vibrating on climb through FL340. The vibration could be felt through the airframe. The N1 was reducing and fluctuating, and the fuel flow was reducing. The engine was shut down and the aircraft returned to Sydney.

Maintenance checks found water in the engine fuel control unit. When this was drained the engine operated satisfactorily. The source of the water could not be determined.

Flight idle RPM was not attainable on No 2 engine during descent into Hobart. Maintenance action was to lubricate the power plant control system, subsequent operations were normal.

Take-off was aborted when No 1 oil quantity dropped to zero concurrent with lack of acceleration of the No 1 engine. The oil quantity gauge was found to be faulty and was replaced. Maintenance adjusted the power lever rigging and subsequent operations were normal.

The aircraft was given a requirement to reach FL310 by a specified time (43) in order to gain separation from opposite direction traffic at FL290. After the specified time (at 44) the pilot reported that he was unable to reach FL310 and was unable to maintain FL300. The aircraft was given immediate descent to FL270. Shortly afterwards the pilot advised that he was able to climb to FL310. A procedural breakdown in separation with the opposite direction traffic occurred.

The crew reported that they had maintained the climb rate using the vertical speed of the aircraft autopilot. This had caused the airspeed to decay because the climb performance of the aircraft was unable to sustain the climb rate demanded. It then became necessary for the aircraft to descend in order to regain its speed and performance.

After an aero tow to 2000 feet above ground level, the two seat Grob glider descended before the pilot located a thermal. The flight was to give a visiting Japanese glider pilot an experience of gliding in Australia. Two other gliders were launched, and they commenced thermalling in an adjacent thermal.

The Grob pilot later joined the other gliders in their thermal and remained there while climbing from 2500 feet to 3000 feet above ground level. With the other gliders still in the thermal and at least 200 feet higher, the pilot elected to leave and tracked north at 50 knots. A short time later the glider experienced a collision, and the pilot observed another glider immediately above and overtaking.

Suspecting tail damage, the pilot elected to conduct a descent at low speed without the use of dive brakes. The descent in sinking air took about 20 minutes. Both aircraft landed uneventfully.

The pilots later concluded that the single seat glider had departed from the thermal shortly after the two-seater, without the pilot of the single seat aircraft being aware that the other had left. They both departed in the same direction. Because the inter-thermal speed for the single seat glider was 70 knots the pilot accelerated to that speed, using the 200 feet of vertical separation that had existed with the two-seat glider. The result was that neither pilot was able to see the other aircraft prior to the collision.

Due to smoke haze conditions, the senior tower controller had advised other controlling agencies some hours previously that the tower could not exercise visual separation in the circuit area. Aircraft were being provided with radar separation for landing.

When the two subject aircraft were approaching for a landing on runway 14, the slower aircraft was in front. That aircraft was asked to maintain its best possible speed and the following aircraft was slowed as much as possible. Separation reduced to below the radar limit when the aircraft were on final approach, with the second aircraft still unable to see the aircraft in front, about three miles ahead. Both aircraft landed safely.

The approach controller had not taken sufficient action to ensure that the aircraft were adequately separated during the approach to land.

FACTORS

1. Smoke haze reduced visibility.

2. The approach controller did not provide adequate separation to the landing aircraft.

Sequence of events

The workload on the Arrivals sector at the time had been low with a number of aircraft on frequency but little radio work or co-ordination to conduct.

Two Boeing 737s, VH-TAI and VH-CZF, inbound from Brisbane via route T53 were cleared to descend by the Arrivals controller, TAI to Flight Level 220 (FL220) and CZF to FL330. TAI was also cleared to track direct for a 16 NM final for runway 01.

Another B737, TAF, was overflying Townsville en route from Brisbane to Cairns, initially maintaining FL350. Prior to reaching the area controlled by Townsville Approach the crew was instructed to operate the aircraft's transponder on a discrete code to indicate to the Approach controller that it was overflying. Normally, when aircraft are about 35 NM north of Townsville and this system is in use, pilots are instructed to select their normal transponder code.  They are then handed off to Cairns radar and later instructed to contact Cairns Control.

The radar system in use at the time was not capable of presenting information to facilitate aircraft identification on the radar screen so the controller had to maintain a plastic indicator (known as a "shrimp boat") to indicate each particular aircraft.

The over-flying aircraft was instructed to change to normal transponder code and was cleared to descend to FL210 in accordance with normal procedures. However, the hand-off to Cairns was not conducted and the investigation could not determine how accurately the "shrimp boat" position was maintained. The Cairns controller subsequently queried the position of TAF, and the aircraft was then handed off between controllers.

About this time, a C130 aircraft departed Townsville for Amberley along an outbound track of 155 degrees and climbing to FL210. The Arrivals controller did not generate a "shrimp boat" for the C130 at that time although this was his normal practice. When the C130 had reached about 30 NM south of Townsville, the other aircraft inbound from Brisbane, TAI and CZF, were entering the lower portion of the radar screen at about 85 NM from Townsville and coming under the control of the Arrivals controller.  Both aircraft were close together and conducting a stepped descent that had been arranged with a previous controller. That controller had advised the Arrivals controller that he had limited the descent of TAI to FL220 due to the C130 climbing to FL210. This level had been recorded on the flight strip being used by the Arrivals controller for TAI.

In order to identify both aircraft the controller instructed the crew of TAI to select their transponder to standby. This aircraft was slowly diverging from CZF and tracking direct to a 16 NM final position to the south of

Townsville. The "shrimp boat" for the over-flying aircraft, TAF, was incorrectly moved to the screen indication (radar paint) for TAI, while another "shrimp boat" for CZF was created.  After a report by TAI, CZF was cleared to a new level.  No entry was made on the flight strip.

After identifying CZF, the controller wanted TAI to display its normal transponder code in order to identify that aircraft.  He incorrectly addressed his transmission to TAF, whose pilot acknowledged and added the information that he was approaching FL210.  The aircraft was cleared to descend to 9,000 ft and the Townsville QNH was given.  A frequency change instruction was issued to another aircraft and the Cairns controller advised that he had not yet heard from TAF. By that time TAF was no longer painting on the Townsville radar screen. The Arrivals controller instructed TAF to call Cairns Control and passed the correct frequency. Shortly after this instruction, because the aircraft he was observing as TAF had not displayed the correct transponder code, the controller again instructed TAF to select its normal transponder code and to use the "ident" facility.

The Cairns controller again contacted the Townsville Arrivals controller to ask why TAF had been given descent to 9,000 ft in Cairns' airspace.  It was at this time that the Arrivals controller realised that he had confused callsign's of the two aircraft. He then advised TAI to select its discrete transponder code and "ident".

Prior to this time, the Approach controller had wanted to hand the C130 off to the Arrivals controller. On looking across the room he realised that the Arrivals controller was busy attempting to identify two aircraft. The second Arrivals controller was also returning to the console and was aware that the controller was involved with talking to aircraft and conducting co-ordination simultaneously. He began to configure the console for two- controller operation. The Approach controller elected to retain control of the C130 until he was satisfied that the other controller could accept the aircraft. He was aware that the inbound track of TAI would pass close to the outbound track of the C130.

As soon as the Arrivals controller had obtained a transponder return, and without advising the crew of TAI that their aircraft was identified, he cleared the aircraft to descend to 9,000 ft.  As there was adequate radar separation between TAI and CZF, he also cleared CZF to descend to 9,000 ft. The Approach controller overheard this clearance given to CZF and went to the radar screen and pointed at the C130 return.  He was waved away by the Arrivals controller. The Approach controller and the new Arrivals controller co-ordinated rapidly and directed the C130 to maintain FL170 and TAI to maintain FL180. Shortly afterwards the pilot of TAI reported that he had just passed a C130. The strips for TAI and CZF did not reflect the levels to which both aircraft had been cleared.

CONCLUSION

Findings

1. While attempting to resolve the traffic situation, the Arrivals controller confused the callsigns of TAF and TAI.
2. After identifying TAI and CZF on radar, the Arrivals controller cleared both aircraft to descend to 9,000 ft causing a loss of separation standards between the climbing C130 and TAI.

Significant factors

1. The controller did not follow local procedures to ensure that aircraft were correctly identified on the radar screen.
2. The controller became confused and lost perception of the air traffic situation.

The pilot of VH-WLC used the wrong callsign when commencing to taxi (i.e. VH-KEW). He changed to the correct callsign when ready to take off and advised ATC. The controllers had strips for both callsigns and changed the callsign on the strips initially used instead of changing strips. As a result, ATC had the aircraft route and altitude incorrect. Calls made by the pilot after take-off were mis-heard by the controllers.