The captain reported that during the landing roll, while decelerating through approximately 40 knots, the nosewheel entered a soft patch on the dirt strip. The aircraft slewed slightly to the right and the nosewheel broke through the rolled crusted surface of the strip. This resulted in the left side of the aircraft being sprayed with large stones, causing damage to the engine, left flap and left wing. The crew (captain and co-pilot) inspected the damage, and the captain elected to fly the aircraft back to Essendon for repairs.

After arrival at Essendon, it became evident that the damage was more extensive than it appeared when the aircraft was inspected by the crew immediately after the occurrence.

Some of the communication problems appeared to be attributable to the similarity of several of the aircraft callsigns. It is probable that the use of HF communications with some aircraft also contributed to the controllers' communication difficulties.

The pilot of VH-PJM was enroute Forbes to Brewarrina at 6,000 ft initially estimating Nyngan at 0941 EST but later revised the estimate to 0931. The pilot of VH-XMM was enroute Walgett to Hamilton at 6,000 ft initially estimating Tottenham at 0910 but revised the estimate twice, the last being 0921. Based on the original flight plan/ flight progress strip estimates for both aircraft, the time of passing in the Tottenham area would have been 0905 with PJM approximately 45 NM south-south-east of XMM.

The pilots revised their estimates enroute because XMM encountered a headwind component whereas PJM encountered a tailwind component. However, by the time the Flight Service operator had passed traffic information to both pilots, both aircraft had passed within 5 NM of each other at 6,000 ft.

The Flight Service operator advised that at the time of the breakdown in separation his traffic workload was fairly high. He failed to realise that the revised estimates placed both aircraft in the Tottenham area at approximately the same time.

The pilot of VH-NPD, operating IFR and tracking from Port Augusta to Adelaide at 7,000ft, requested Adelaide Flight Service for a change of altitude to 9,000ft. Adelaide Flight Service arranged the altitude change and advised there was no other IFR traffic in the area.

VH-JVN, another IFR aircraft, had been cleared direct from Adelaide to Leigh Creek at 9,000ft, and therefore not assessed by air traffic control as traffic for NPD. The flight route was later changed to via Ardrossan, which put it on a reciprocal heading to NPD. The possibility of a conflict was not recognised by the sector controller before the two pilots had become concerned about the situation and arranged their own separation.

The aircraft passed each other within 1km at the same altitude.

Following touchdown, the aircraft bounced twice and veered to the right, before the left main gear collapsed. The aircraft came to rest on its left wingtip. The wind conditions during the landing were not favourable for the tail-wheeled aircraft.

The wind strength was 10 kts and all crosswind from the right. The pilot lost directional control of the aircraft, probably due to weather cocking.

Factual information

Description of the airspace layout near Brisbane

Controllers are each responsible for pieces of airspace, called sectors. In general, aircraft within each sector were required to have radio communications with the controller responsible for that sector. Airspace involving coastal airways to the north of Brisbane was in sector 3B. Airspace in a similar area to the south of Brisbane was in sector 2G. The boundary between these two sectors was a line between Amberley, Archerfield, Brisbane and the 091 VHF Omni-directional Radio Range (VOR) radial from Brisbane. Sector 4M controlled airspace beyond 30 NM to the east and west of Brisbane, including the Amberley control zone and airspace above. The area up to and including FL200 within 30 NM of Brisbane, excluding the Amberley control zone, lay in the Brisbane Approach area.

History of the flights

Kiwi 185, a Royal New Zealand Air Force C-130, was tracking from the west of Brisbane to overhead Brisbane and then eastbound along the 089 Brisbane VOR radial at FL290. Its estimated time of arrival overhead Brisbane was 1345 hours local time. When near Brisbane, the aircraft should have been handled by sector 4M until about 20 NM west, then sector 3B until 30 NM east of Brisbane, before being handed back to the sector 4M controller. Because the aircraft would be in sector 3B airspace for only about 50 NM, that controller elected to leave the aircraft on sector 4M's frequency. Due to crossing traffic in a sector to the east of 4M, east of Brisbane, FL290 would not have been available. The aircraft was given a requirement to descend to FL270 before 1400. The sector 4M controller passed this instruction to the aircraft at 1335, after checking with the sector 3B controller and confirming that there were no other requirements for the aircraft. Some time later the sector 4M controller also informed sector 2G that Kiwi 185 had been assigned FL270, with a requirement to reach that level by 1400.

VH-TAF was to track from Maroochydore via TRIKI (32 NM on the 010 radial from Brisbane VOR) to Brisbane and then towards Sydney. The aircraft departed Maroochydore at 1337, on climb to FL350. Initially the aircraft would pass from Maroochydore airspace to sector 3B airspace, however the sector 3B controller had the aircraft call Brisbane Approach instead. After leaving Maroochydore the aircraft should have been handled by sector 3B until 30 NM from Brisbane, when it should have been handed off to Brisbane Approach. If the aircraft then climbed above FL200 before reaching overhead Brisbane it should have been handled again by sector 3B until overhead Brisbane, at which time it would have come under the control of sector 2G. At 1340 the aircraft was at TRIKI, and passing FL130, when the crew called Brisbane Approach. After this time the sector 3B controller discarded the flight strip for this aircraft. The climb performance of the aircraft was such that it was above FL200 before reaching Brisbane, in which case the aircraft should have again been under the control of the sector 3B controller. At 1342 the approach controller noticed the track of Kiwi 185 at FL290 and imposed a climb restriction of FL280 on VH-TAF because of the approach of Kiwi 185. The controller informed the sector 2G controller that the aircraft was being held at FL280 until a stable return was received on Kiwi 185. As the sector 2G controller assumed that the sector 3B controller was separating the two aircraft, and that descent clearance for Kiwi 185 would not be issued until that aircraft was east of Brisbane, the approach controller was not informed that Kiwi 185 was actually assigned FL270.

Kiwi 185 entered the cone of silence overhead Brisbane radar at 1344. The cone of silence is an area above the radar transmitter in which the radar is unable to receive signals from the aircraft. Aircraft in the cone of silence are lost from the radar screen until they are detected on the other side of the cone of silence. VH-TAF entered the cone of silence some 30 seconds after Kiwi 185, shortly before the crew reported approaching FL280. The approach controller held the aircraft at that level until both aircraft had emerged from the cone of silence. Around this time the controller in sector 3B changed. VH-TAF was cleared to climb to FL350 just before 1348, when lateral separation with Kiwi 185 had been achieved. Kiwi 185 commenced descent and reported to the sector 4M controller some 12 seconds after VH-TAF was cleared to climb to FL350.

Analysis

Sector 3B controllers were trained to be aware that some aircraft climbing from Maroochydore can be above approach airspace before passing Brisbane. Their need to check for possible conflictions with traffic overflying Brisbane was, therefore, regular but infrequent. As the controller's attention was normally focussed on the 99% of traffic outside of 30 NM from Brisbane, a positive action to consider traffic inside that distance was required. The two aircraft were the responsibility of this controller overhead Brisbane, but the controller did not recognise the confliction. After VH-TAF had entered Brisbane Approach's airspace, the sector 3B controller discarded the flight strip for that aircraft. It was evident that the controller had not considered the possibility of VH-TAF re-entering sector 3B airspace before reaching Brisbane, nor had the possibility of a confliction with Kiwi 185 been considered. In addition, the controller had not identified Kiwi 185 to sector 2G, nor informed the sector 2G controller of the descent requirement for Kiwi 185. That information was ultimately relayed by the sector 4M controller.

The Approach controller had noticed that VH-TAF and Kiwi 185 would conflict, so took steps to ensure vertical separation between the two aircraft. Both aircraft were outside the Approach controller's area of responsibility. Co-ordination was conducted with the sector 2G controller after this action was taken, but that controller did not mention the descent requirement for Kiwi 185. As a result, the Approach controller was not aware that Kiwi 185 could have initiated a descent at any time. Such a descent would have caused a breakdown in separation standards between the two aircraft. Fortunately, the descent did not take place until other separation standards had been obtained.

The sector 2G controller was aware of both aircraft and the conflict but assumed that the sector 3B controller was providing the separation. This aspect was not positively checked with the other controller, nor did the sector 2G controller warn the Approach controller that Kiwi 185 might descend at any time.

Both aircraft were on different radio frequencies so the crews would not have been aware of each other through radio transmissions.

Significant factors

1. Controllers did not ensure that aircraft were operating on radio frequencies relevant to the airspace in which the were flying.
2. The sector 3B controller did not ensure separation for all aircraft in the sector.
3. The sector 3B controller did not maintain a flight strip to cover the full period for which VH-TAF was in the sector.
4. The sector 2G controller assumed that the sector 3B controller was ensuring separation for traffic near the boundary of both sectors.
5. Co-ordination between controllers was inadequate.

Safety action

As a result of this incident, Airservices Australia Northern District management have recommended the following actions:

1. That aircraft contact the responsible sector for clearance to levels above approach airspace. Such aircraft would be held in approach airspace (maximum FL200) until handed off to the responsible sector. This would provide positive separation to overflying traffic.
2. A review of the terminal area altitude cap (FL200).
3. That the need to retain flight progress strips until an aircraft is clear of a sector's responsibility be reiterated.

The pilot of the Pawnee Brave was conducting a procedure turn to the right, at the end of a spray run. At a height of about 150 ft he heard a loud bang, felt the aircraft shudder, and saw flames passing down the left side of the engine cowling. From the apex of the turn, at a height of about 250 ft, the pilot elected to land in an open field adjacent to the wheat crop he had been spraying. He kept the engine running, as it was still developing some power, until the landing was assured Before he had crossed the boundary fence, the cockpit had started to fill with smoke.

Once the landing was assured, the pilot completed the emergency shut down checks and landed. His vision was obscured by engine oil on the windscreen, smoke in the cockpit and flames and smoke outside the aircraft. After landing, the pilot found that directional control and braking were hampered due to the left brake failing. Once the aircraft had stopped the pilot was able to escape safely but was unable to extinguish the fire with the portable fire extinguisher. The aircraft was totally burnt out within 30 minutes.

A subsequent examination of the wreckage found that a cylinder had separated on the left side of the engine, fracturing a fuel injector line. Fuel had sprayed onto an adjacent high tension ignition lead conductor, which was shorting to the sparkplug body. The left brake failed due to the airborne fire burning through a flexible hydraulic brake line.

FACTUAL INFORMATION

A Piper PA23 aircraft, VH-MBU, on a right base leg for runway 15 conflicted with a Boeing 737 on left base leg as a result of a co-ordination breakdown.

VH-MBU was inbound from Stoney Creek and the Approach 2 controller co-ordinated with the Tower Controller to process the aircraft via right base leg behind a Boeing 747 on final approach for runway 15. The pilot was asked to sight the B747, which he did. The pilot was then told to contact the Tower. There was no co-ordination with Approach 1. The Approach 1 controller had transferred a Boeing 737 VH-TAK, to the Tower and asked Approach 2 what he was doing with MBU and should TAK be following MBU, to which he replied in the affirmative. TAK was turning left base on Tower frequency by this time. Co-ordination with the Tower Controller alerted him to the confliction. The Tower Controller advised MBU to orbit right base and TAK was allowed to continue with the visual approach.

Radar data confirmed that the two aircraft conflicted with a separation of 1.5 NM at the closest point of approach.

ANALYSIS

The Approach 2 controller failed to co-ordinate the landing sequence with the Approach 1 controller. The reason for this lapse in performance was not positively established but the controller's supervisor thought that a desire to provide an expeditious service may have been a contributing factor.

The helicopter was on a scenic flight over the Bungle Bungle National Park. As it passed an outcrop it appeared to be rocked by turbulence. The helicopter yawed to the right and commenced an uncommanded descent. The pilot stopped the descent and checked the engine indications. Although no warning lights were illuminated the rotor and N2 RPM were still increasing. The pilot was able to stop the N2 overspeed at 104 per cent. He turned the helicopter towards the airfield and commenced a cruise descent. As the helicopter descended through 150 ft, on final approach, the engine-out alarm sounded, and the pilot heard the turbine RPM decreasing. He turned the helicopter into wind and completed an autorotational approach, landing short of the airfield. After landing, the pilot observed the engine was still operating at idle RPM.

Post-landing inspection disclosed damage to the tail boom, probably as a result of a heavier-than-normal touchdown.

It was reported the rotor and N2 RPM problems were the result of a sheared engine governor drive shaft.

FACTUAL INFORMATION

The controller started acting as the Aerodrome Controller (ADC) at 1100 local time. Up until 1120, the workload was described as being light. At 1120 the ADC was responsible for one helicopter under the final approach path of runway 32, at three miles from the field and operating not above 500 ft. Another helicopter was flying from the north of the aerodrome towards the same area and had been directed to track to the west of the aerodrome. A third helicopter was waiting at Burleigh for a clearance to enter the zone. A Piper PA28 was about two miles from the runway, on final for runway 32. Two jet aircraft were also approaching final for runway 32, and were about 15 and 22 NM from the airport. An Airbus A320 reported ready at the holding point for runway 32. That aircraft was given a clearance to line up.

Because of the short distance from the parking area to the holding point, the controller was aware that airline aircraft sometimes take a long time to actually line up at the threshold. The cabin crews on the aircraft often need a considerable period of time to complete their briefings and the pilots taxi slowly to avoid stopping the aircraft. The taxiway for runway 32 was situated about 400 m from the threshold of runway 32, with the result that the time taken for aircraft to be ready for take-off could vary. On this occasion the Airbus was reported to have been slow to line up.

The ADC asked the pilot of the Piper if he would accept a landing on runway 35, a 552 m long strip which crossed the main runway about 850 m from the threshold of runway 32. The change was accepted and the pilot was asked to report on final approach. The helicopter under the final approach path was asked how long he wanted to remain there, and was then told to report on completion of his activities. The ADC then cleared the Piper to land on runway 35. Another aircraft reported ready to line up, and the ADC instructed that pilot to hold at the holding point. A helicopter previously cleared to track northbound east of the coast from Point Danger to Burleigh was asked to make an orbit or hold due to a jet aircraft about to take off and turn right.

Departure instructions for the Airbus were obtained from the Approach Controller and the ADC cleared the aircraft for take-off, followed by a right turn to a heading of 120 degrees. During this process he reported checking the radar screen and runway 32. He did not check the flight strips. The controller then devoted his attention to the helicopter under the final approach path for runway 32. He initially asked the pilot to fly to the west of the final path for about three miles. In response the pilot informed the ADC that he was finished in the area and requested a clearance to track to Surfers Gardens.

When a break in this interchange occurred, the pilot of the Airbus informed the controller that the other aircraft was now clear of his path, and asked to confirm whether he was clear to take off. This was re-affirmed. The pilots of the Piper had heard the Airbus being given a take-off clearance and had been prepared to go around if that aircraft began to roll. The pilots of the Airbus had seen the Piper during their pre-take-off scan and had waited until the aircraft had crossed their runway.

As the Piper was originally to land on runway 32, the ADC had that runway marked on the flight progress strip. When the runway was changed the new runway should have been marked. This was not done. In addition, when the second runway was activated he should have notified the Surface Movement Controller. This was not done, reportedly because the aircraft was close to landing and the second runway would only have been active for a short period of time. The controller workload at Coolangatta was described as becoming busy irregularly. During a normal working week controllers were often on duty in the various positions when activity was low.

The controller estimated that he was only able to achieve about two hours per week when the activity was moderate to busy. As a result, he found it difficult to maintain a system which catered for the busy periods. Most of the time he was able to remember the complete aircraft activity picture without reference to the various systems to aid memory, such as the flight progress strips. The investigation was also informed that tower controllers often did not maintain current information on the flight strips when activity became high. There was a need to retain the activity picture in their mind as well as maintaining the information on flight strips, and this latter aspect often lost priority.

Prior to issuing a take-off clearance the controller reported that he should have scanned the runway, the circuit area, the apron and taxiway, the flight progress strips, the active bay, and the radar. On this occasion he did not do all of these actions. He attributed this to the irregular activity pattern which was not conducive to a regular scan.

No deficiencies in workstation layout or visibility from the control tower were found. Ranges to the west of Coolangatta could have made the Piper difficult to see when it was on final approach and close to the runway. The radar display was "gated" so that aircraft within one mile of the runway were not displayed. This was done to avoid the display becoming crowded with returns of aircraft on the ground. Depending on the position of the Piper aircraft, it may have not been displayed on the radar.

During the four days prior to this incident the controller had been suffering from the effects of a virus. Although he had initially started the day not feeling like going to work, by the time he had arrived he was keen to be working.

ANALYSIS

The term 'mental workload' refers to the difference between the amount of information processing resources required by a situation and the amount of such resources available to the person at that time. The controller was probably experiencing a significant mental workload around the time of the incident. The control situation at the time involved a significant number of different aircraft, producing an unusual task load. Although the controller rated the workload as moderate, there were periods of radio communication without significant breaks. The controller's ability to cope with the situation may have been degraded by a lack of proficiency and his recent health, although the influence of these factors could not be established.

The controller was in the habit of retaining all the relevant information and the operational picture in his memory. This meant that he was not in the habit of conducting a full sequence of checks prior to issuing a take-off or landing clearance. One of these checks involved a scan of the flight progress strips. When his workload became high, he was in the habit of allowing activity on the flight progress strips to lapse, in favour of retaining his mental picture. That was the situation on this occasion. He probably developed a "loop", whereby he did not scan the strips because he knew they were not accurate.

When the pilot of the Piper was asked to use runway 35, the aircraft was not far from landing. As far as the controller was concerned it would not be long before that runway was no longer in use. He did not comply with the procedure to notify the SMC of the runway's activation because of the short time the runway would be in use. This action created another gap in the separation assurance of the two aircraft involved. It also excluded the other controller from any cross-checking capability.

The ADC's workload had become high very quickly and he had some problems, other than the aircraft landing on runway 35, that needed his attention promptly. The evidence indicates that he omitted the Piper from his thinking as soon as it had been cleared to land. When runway 32 was scanned prior to giving the Airbus a take-off clearance, the Piper was not seen as it was not near this runway. When the radar was scanned, the Piper was probably inside the area which was not displayed on the screen. The only other prompts which could have reminded the controller about the Piper were a scan of the strips and a strip indicating that runway 35 was active. It is likely that he would have been reminded about the presence of the Piper if he had scanned the strips, even though he had not kept them up to date.

The potential for a more serious incident was averted by the crews of the two aircraft. Both crews were aware of the other aircraft and were prepared to take avoiding action. The crew of the Airbus did not commence take-off until the other aircraft was clear of their runway. They also checked again with the controller to ensure that everything was in order for their departure. The crew of the Piper were prepared to go around and take other avoiding action if the Airbus began its take-off roll. For these reasons, a serious incident involving an inadvertent breakdown of separation was not likely.

FACTORS

1. The controller was experiencing a high level of mental workload.

2. The controller was not maintaining accurate flight progress strip information.

3. The controller did not take the appropriate steps to activate runway 35.

4. The controller forgot about the Piper after issuing a landing clearance.

5. The controller did not scan all the available information prior to issuing the Airbus a take-off clearance.

6. The pilots of both aircraft maintained sufficient situational awareness to avoid each other.

SAFETY ACTION

The use of the team concept by Airservices Australia is being examined by the Bureau as a result of previous incidents. The details of this incident will also be considered during that research.