Circumstances

The Arrivals North Controller [ARRN] had commenced duty at approximately 0705 EST and was experiencing a period of heavy air traffic. He had requested the previous occupant of the position to remain at the console in the monitor position to assist him in a settling-in period. This controller was in the monitor position during the events of this occurrence.

The FLOW controller had decided that he would request the use of Sector 8 airspace for three aircraft to reduce the workload on the arrivals controller and reduce the delay to the aircraft. The Sector 8 controller agreed to the request and raised the required flight progress strips [FPS] for his own reference. After receiving instructions from the FLOW controller to track both VH-TQO and VH-TQQ via Richmond, ARRN proceeded to process the two aircraft onto that track, a track that would take them clear of the main arrival route of Singleton to Sydney.

VH-TQO was proceeding at Flight Level [FL]190 on a flight from Tamworth to Sydney. At 0718 ARRN instructed VH-TQO to track direct to Richmond and thence to Sydney. This resulted in the aircraft tracking approximately 210 deg. VH-TQQ was proceeding at FL160 on a flight from Port Macquarie to Sydney and was on a similar track to that of VH-TQO and approximately 12NM behind. At 0721 ARRN instructed VH-TQQ to track direct to Richmond and thence Sydney.

This resulted in the aircraft tracking approximately 200 deg. At 0722 ARRN handed to Sector 8 the identification on VH-TQO with the assigned altitude of 8,000ft. This was accepted by Sector 8 who wrote this altitude on the FPS for VH-TQO. Both aircraft were then descended to 8,000ft by ARRN and at 0724 the controller, intending to transfer VH-TQO to Richmond Approach, mistakenly instructed VH-TQQ to contact Richmond Approach [Sector 8]. VH-TAF was on descent to FL200 on a flight from Coolangatta to Sydney and was tracking on the main arrival route from Singleton to Sydney.

At 0726 ARRN instructed VH-TAF to descend to 8,000ft. When VH-TQQ contacted Sector 8 the controller acknowledged with the callsign TQQ but notated the details on the FPS for VH-TQO. At 0726 the Sector 8 controller had a departure from Richmond that was conflicting with VH-TQO and elected to vector VH-TQO in order to maintain separation. He issued VH-TQQ, the aircraft on his frequency, with an instruction to turn left heading 140 for separation. The crew obeyed the instruction but were approximately 12 NM north of the point the controller thought the aircraft was passing.

The controller saw that VH-TQO was not turning and issued a further left turn to a heading of 120 to VH-TQQ. This placed VH-TQQ on a track that would conflict with VH-TAF. ARRN did not immediately realise that VH-TQQ had turned back towards the main Singleton to Sydney track and it was the arrivals controller in monitor who first saw the new position of VH-TQQ and initiated recovery action. At about the same time the crews of both VH-TQO and VH-TQQ started to question the control instructions and asked if there had been a transposition of the callsigns.

At 0728 ARRN instructed VH-TAF to turn left immediately onto a heading of 090 deg. to place that aircraft on a heading away from VH-TQQ. Flight levels were then checked and vertical separation established until radar separation could again be guaranteed. Radar analysis showed that there was no breakdown in separation as vertical separation existed at all times during which horizontal separation was not provided.

The callsigns were very similar and belonged to the same type of aircraft in the same company. Anecdotal evidence and statements from the persons concerned in this occurrence, indicate that this confusion has often arisen because of the common feature of these two aircraft being processed for arrival or departure at similar times. During the course of the interviews five controllers complained of the two callsigns being on frequency together and having had trouble with them at some time or other.

The crew of VH-TQQ were expecting to be given the radio frequency change to Richmond Approach at the time the ARRN controller issued the instruction and, therefore, had no reason to query the instruction. The O and Q do not readily stand out from one another on the digital read out of the radar display and this can lead to a confusion of callsigns in high density traffic situations.

Significant Factors

1. The callsigns TQO and TQQ are very similar and do not stand out from each other on the digital read out showing on the radar screen.

2. VH-TQO and VH-TQQ were given the same tracking instructions while proceeding 12 NM in trail.

3. Both the Arrivals North controller and the Sector 8 controller used the callsign TQQ when intending their transmissions to be for TQO.

Safety Action

Since the above incident a further occurrence has been reported to the Bureau. On 23 March 1994 a controller at Sydney transposed the callsigns and issued a clearance to TQO which was intended for TQQ. On this occasion there was no further incident as the pilot queried the callsign immediately and corrective action was taken.

Recommendation

R930316

With the above occurrences in mind, the Bureau of Air Safety Investigation recommends that Qantas Airways: Change the registration of VH-TQQ to avoid confusion with other callsigns.

About 5 minutes after take off the engine began to run roughly. The aircraft returned to Hoxton Park and after landing the pilot found the fuel strainer full of water. The aircraft had been refuelled about 10 days before from a ground installation and had remained in the open since then. Investigation revealed that no other operators who had refuelled from the same installation had suffered from water contamination. The fuel installation is a modern style appliance with a water sensing element which automatically shuts itself down if water is detected.

It was not determined how the water got into the fuel system but there had been periods of heavy rainfall whilst the aircraft had remained in the open and it is possible that water had leaked in through the fuel caps.

The aircraft lost power shortly after take-off. A successful forced landing was made in a field adjacent to the strip. An inspection of the aircraft disclosed that a hose directing cooling air to the fuel injector manifold was kinked restricting the amount of cooling air available at the manifold. It is suspected that the manifold overheated and vapourised the fuel causing the loss of power experienced by the pilot.

The nose landing gear collapsed during the take off roll causing both propellers to strike the runway whilst operating at full power. Subsequent investigation revealed that a rigid hydraulic line had failed causing the loss of all hydraulic pressure. This lack of hydraulic pressure probably allowed vibrations to unlock the nose leg over-centre lock during the take off roll.

Examination of the failed hydraulic line revealed that there was thinning of the pipe wall at the failure where the pipe was supported by a 'P' clamp, possibly the result of corrosion. Significant Factors: Failure of a hydraulic pressure pipe, possibly due to corrosion, resulted in loss of all hydraulic pressure. The nose landing gear over-centre lock probably unlocked due to vibration.

The pilot of VH-TQL reported that when on short final for runway 12 the crew noticed a displaced threshold for runway 30 and men and vehicles commencing to enter the closed off area. No NOTAM for this activity was current and this was confirmed by the AVFAX help phone number. The RAAF advised that there had been a self cancelling NOTAM for work on the cable-hook arrester system on the previous day, and the work continued the next day but relevant authorities were not advised. Upon ascertaining that the work was continuing, the tower controller had immediately arranged for a Sydney NOTAM to be raised but it was not issued prior to the arrival of VH-TQL. Measures have been taken by the RAAF to prevent a recurrence.

After departing Canberra from runway 35 at 0744, the aircraft was observed by radar to correctly follow the assigned standard instrument departure. However, the pilot failed to transmit a departure report on departures frequency 125.9 and contact could not be established on tower, departures, approach or sector frequencies. At 0749 an uncertainty phase was declared. The aircraft was observed to be following the cleared route, Canberra to Bindook via Cullerin and at 0756, the pilot contacted Sydney arrivals and requested descent.

The uncertainty phase was then cancelled by Sydney Control. The crew of VH-TJO were interviewed by the company training manager, and although the captain could not specifically recall contacting Canberra Departures, it appears that the Sydney FIS frequency 125.7 MHz was incorrectly selected in lieu of 125.9 mhz. When a descent clearance was requested Sydney FIS directed the crew to the correct frequency.

Following an extended flight over water, the helicopter suffered a power loss as it was approaching the coast. The pilot conducted an autorotational descent and landing. The landing on coastal mud flats was heavy, resulting in damage to the skid gear and tail boom. Examination by a Licenced Aircraft Maintenance Engineer (LAME) found that there were blockages of both venturis in the fuel transfer system which prevented the flow of fuel from the two forward tanks to the main fuel tank which supplies the engine. The engine had been running following the forced landing. The fuel supply was obviously not blocked completely, but sufficiently to prevent operations at normal flight power settings. The material blocking the two venturis appeared to consist of tiny specks of fuel tank liner.

The helicopter was being positioned at the North Rankin "A" Platform to transport passengers back to Karratha. When the helicopter arrived on the helideck it was landed into a strong south-westerly wind and positioned into wind with the pilots' eye-line between the two lines painted on the helideck. The pilots elected to shut down the engines when they were told that the passengers were delayed.

They did not reposition the aircraft, so that it was offset from the wind, prior to shutting down the engines, as required by company procedures. Wind tunnel test results for the rig helideck platform show that turbulent airflow over the helideck can be expected under the wind conditions prevailing at the time of the accident. The pilots confirmed that the wind on the helideck was different to the free-stream air flow. They noticed that there was a strong updraft in the vicinity of the leading edge of the helideck.

As a result of a safety audit conducted several months prior to the accident, the company pilots were required to land their helicopters with their eye-line at or very close to the outer of the two lines on the helideck. The helicopter was landed between the two lines with the main rotor disc protruding over the leading edge of the helideck. When the engines were restarted after the passengers were boarded, the blades were seen to rise during the initial couple of revolutions as they came into the view of the cockpit.

At about the same time a noise was heard from the rear of the helicopter and a vibration was felt. The start was discontinued and inspection found that the tail rotor drive shaft had broken at the rear end. Subsequent investigation revealed that the main rotor had struck the drive shaft which had then failed. It is probable that the strong updraft in the vicinity of the leading edge of the helideck caused the advancing main rotor blade to rise and the retreating blade to consequently dip, resulting in the main rotor strike.

The aircraft was cleared by Townsville Sector 1 to track Mackay-Capricorn-Rockhampton at 9000 feet. This clearance was coordinated with, and acknowledged by, Rockhampton Tower. The cleared route tracked through the Shoalwater Bay military training area and a number of restricted areas in this vicinity were active. The error was detected when the aircraft called Rockhampton Tower at 28 miles on the Capricorn-Rockhampton track.

There was significant military air traffic transiting from Townsville to the exercise area and in the area itself. Throughout the morning, there had been frequent changes in the activity state of the various restricted areas (there were 9 notams current at the time of the incident). Consequently, the Sector 1 workload was very high. The display showing the status of the restricted areas at the Sector 1 console had been adjusted to reflect the activity states but was open to misinterpretation as to which areas were active and which were inactive.

The Sector 1 controller interpreted the display as indicating that the restricted areas were inactive and cleared the aircraft via Capricorn. At the time the clearance was coordinated with Rockhampton Tower, the controller involved was distracted and did not clearly hear the cleared route. He assumed that it must have been via reporting point Murph, which would have taken the aircraft to the west of the restricted areas.

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

1. The workload in Townsville Sector 1 was very high.

2. The Sector 1 display on active restricted areas was not unambiguous.

3. The Sector 1 controller misread the display and cleared the aircraft on the incorrect route.

4. Due to a distraction in Rockhampton Tower, the controller did not hear clearly the cleared route as coordinated by Townsville Sector 1.

5. The Tower Controller did not confirm the cleared route with Sector 1.

VH-RBJ (Cessna 310) was proceeding on an IFR flight from Lismore to Cooranbong at 8,000 ft and had passed Coffs Harbour at 1719 hours with an estimate for Taree at 1752 hours. VH-MML (Beech 1900D) had departed Sydney at 1718 hours on a regular public transport flight to Port Macquarie. It was maintaining flight level (FL) 230 and was estimating Taree at 1751 hours. Sydney Flight Service Sector 4 (SEC 4) was operated by one flight service officer (FSO) who considered the workload moderate.

The officer had several flight progress strips (FPS) in his flight progress board (FPB) including one on a Beech 99 that was overflying Taree at 7,000 ft with an estimate there of 1745 hours. When the FSO assessed the traffic situation he gave great consideration to this aircraft but finally decided that it would not effect the other two and elected to pass 'no traffic' to VH-RBJ and VH-MML. He was aware of the possible conflict between these two aircraft but thought he would wait for an update on the position of VH-MML before making any decisions on the matter.

He subsequently lost an awareness of the traffic situation and convinced himself that all conflicts in his area of responsibility had been advised to the pilots. The FPS on VH-RBJ was still in the Coffs Harbour Bay of the FPB but should have been transferred to the next most southerly bay in the geographical layout. At approximately 1740 hours the crew of VH-MML contacted SEC 4 and received the advice of no traffic.

At 1751 hours they then asked SEC 4 if there was any traffic at Taree and the FSO immediately reassessed the situation and realised that the conflict existed. As he was about to inform the pilots of the confliction the pilot of VH-RBJ reported that VH-MML had passed through his level within 2 NM. Both pilots stated that they did not see each other prior to passing. No traffic on each other was passed to either crew prior to the occurrence.

Significant Factors

1. The FSO forgot that the conflict between VH-MML and VH-RBJ still existed after deciding to delay the traffic alert decision until an update position on VH-MML had been received.

2. The FSO did not transfer the FPS on VH-RBJ to the correct position on the FPB.

3. The closing speed of the aircraft made an unalerted see and avoid action unlikely.