A foreign registered Boeing 747 was proceeding from Brisbane Qld to Cairns Qld, via airway H106. The flight was being conducted as a check flight. As the aircraft was being processed for arrival, the crew were cleared to descend to 6,500 ft, which the crew confirmed in their first contact with Cairns Approach. The aircraft's progress was being monitored by Air Traffic Control (ATC) on radar.

ATC instructed the aircraft to expect a left circuit for runway 15 with further descent in 14 track miles. The crew read back "...14 track miles". Shortly after, the controller observed the aircraft's Mode C SSR readout indicating 5,300 ft at 19 NM from Cairns. The radar lowest safe altitude in this sector was 4,400 ft. The crew were instructed to maintain 5,500 ft. Subsequently, the crew reported that the aircraft was clear of cloud and that they had sight of the surrounding terrain.

ATC processed the aircraft via a left circuit for runway 15 at Cairns without further incident.

During the investigation the crew reported that they understood the ATC instruction "further descent in 14 track miles" to mean that they were cleared to descend to 4,500 ft at 14 DME Cairns on a DME arrival. The crew also stated that ATC "was a little bit difficult to understand". Regardless of this perceived difficulty, the crew did not seek confirmation of the ATC instruction.

The recording of the communication between ATC and the aircraft confirmed that prior to this incident no further descent instructions were passed to the aircraft.

SIGNIFICANT FACTORS

1. The crew misunderstood the ATC instruction "further descent in 14 track miles".
2. The crew did not question the ATC instruction before descending below the last assigned level.

The pilot reported that when he landed, the nosewheel was cocked sideways, and collapsed when it contacted the runway. The pilot said the nosewheel steering link was probably broken before the aircraft departed Innisfail. He believes the nosewheel steering may have been inadvertently forced past the steering limit, while being towed.

The failed nosewheel fork was examined by a CASA airworthiness inspector, and in his opinion the nosewheel strut failure was caused by overload after the tyre and wheel failed. He said the possible causes of the tyre and wheel failure could be a heavy landing in crosswind, or the nosewheel impacting with something on the runway.

The strut failed rearwards and substantially damaged the fuselage structure back as far as the wing strut attachments. The cause of the tyre and wheel failure could not be positively determined.

The pilot stated that the purpose of the flight was to visit an engineering workshop in Charleville, and to demonstrate the aircraft which was for sale. Because he wanted to return from Charleville on the same day, and the flight time each way was approximately 4 hours 30 minutes, he had planned for an early departure. When he arrived at the airport, the aircraft was covered in a thick frost, and it took him over an hour to defrost the aircraft and complete a daily inspection. He departed Orange at 0620, and climbed to 6,500 ft. The weather was fine and sunny, but very cold so he pulled the heater control to full on. After passing Bollon, 120 NM southeast of Charleville, the pilot tuned to the Charleville NDB and noted that the needle rotated to indicate straight ahead. He recalled passing a strip about 25-30 miles from Charleville and made a mental note that he could land there if the weather deteriorated. He said that he then started thinking about the descent and recalled thinking about turning the heater down. It appears that the pilot then lost consciousness as the next thing he remembered was that the aircraft was descending through 1,000 ft at about 1,000 ft a minute.

The pilot said he pulled back on the control yoke and saw the horizon come into view. He banked hard left, and the engine coughed. The pilot then noticed what looked like a very long airstrip ahead and landed. After landing the pilot noticed the time was 1230 and realised that his ETA for Charleville had been about 1100. The pilot said his head was aching and he felt cold and nauseous.

The pilot eventually fixed his position roughly 150 NM northwest of Charleville, and after repairing the aircraft radio, he was able make contact with an overflying jet late the next day and was rescued.

Examination of the cabin heat system revealed a large amount of exhaust build-up in the scat hose leading to the cabin heat selector valve. The muffler was badly cracked around the outlet port and had a white soot stain around it. It was concluded that the pilot may have been effected by carbon monoxide which entered the cabin via the cracked outlet port of the muffler.

Approaching Adelaide, the aircraft made numerous diversions from track to avoid weather. On first contact with Adelaide approach, the pilot reported "....taking up a heading of 205 to intercept the localiser for runway 23, descending to 5000” The pilot was instructed to "...maintain 5000 make pilot intercept of the localiser, at this stage expect one holding pattern at Modbury".  The holding pattern was required for separation with other traffic.

The controller stated that the aircraft intercepted the runway 23 localiser beyond 20 NM from Adelaide.  When the aircraft was approximately 17 NM from Adelaide, the controller advised the pilot "...cancel the holding and expect ILS approach, descend to 3000". The pilot then requested confirmation they were cleared for an ILS approach.  The controller instructed the aircraft to "...descend to 2000 on the ILS" and a readback of that instruction was obtained.

A short time later the pilot reported maintaining 2000 ft. The pilot was instructed to maintain 2000 ft and was then asked if they were visual.  The pilot confirmed that they were visual, and the aircraft was then cleared to continue on a visual approach to runway 23.

Recorded radar data showed that the aircraft made a continuous descent from 5000 ft to 2000 ft and passed through

3000 ft at approximately 13 miles from Adelaide.  The aircraft reached 2000 ft at approximately 10 miles from Adelaide. The Adelaide control zone extends to 11 miles from Adelaide on the runway 23 localiser and from 11 miles to 20 miles the lower limit of controlled airspace is 2500 ft.  The descent profile depicted in the recorded radar data suggests that the aircraft was probably below the 2500 lower limit of controlled airspace for a few seconds prior to entering the control zone.

The captain advised that they were using Jeppesen charts and the runway 23 ILS chart has a note which says that aircraft arriving from the northwest may be radar vectored to intercept the localiser at 2000 ft.  The captain said that when they were cleared to descend to 2000 ft they were established on the localiser and both flight crew members thought they were cleared down to 2000 ft at that time.  They had obviously misinterpreted the intent of the instruction. He also pointed out that it is not normal to have a descent restriction imposed once cleared for an ILS approach.

The captain said that cockpit workload was high at the time in that the aircraft was being controlled by the flight management system for an automatic ILS approach.  Both glide slope and localiser had been captured and when the holding requirement was imposed, this created a potential extra workload in reprogramming the flight management system to get out of the approach mode and set up for a holding pattern. Fortunately, the holding requirement was later cancelled.

Factors

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

1. The flight crew misinterpreted an instruction from air traffic control.
2. There was a high workload in the cockpit at the time.
3. The air traffic controller did not notice the aircraft continue its descent below 3000 ft and in fact did not become aware the aircraft had reached 2000 ft until the pilot reported at 2000 ft.
4. The instruction given by the air traffic controller to "... descend to 2000 on the ILS", although correctly read back by the pilot, was open to misinterpretation.

Safety action

The controller was counselled concerning the phraseology of the instruction he gave to the aircraft.  The captain was apprised of the situation from the air traffic controller's viewpoint and a cassette tape of recorded communications relevant to the incident was sent to him for review.

FACTUAL INFORMATION

A British Aerospace 146 (BA146) had departed Brisbane for Proserpine on climb to FL260. Four minutes later a Boeing 747-Special Performance (B747SP) departed Brisbane en route to Taipei on climb to FL350. The initial departure track was the same for both aircraft and was to the northwest of Brisbane. The Brisbane Sector 3B controller believed from past experience, that the rate of climb of the B747SP would far exceed that of the BA146. Consequently, he decided to monitor the horizontal separation on the radar display until vertical separation was achieved.

Approximately ten minutes after departure, the crew of the B747SP observed on the aircraft collision avoidance system (ACAS) display an aircraft ahead and at the same level. From the high rate of closure, the crew estimated that there would be a breakdown in separation very shortly unless action was taken to avoid the aircraft. They requested the Sector 3B controller advise them of the traffic. At the time, the horizontal separation between the aircraft was just over 5 NM and the groundspeed of the B747SP was 100 kts faster than that of the BA146.

The Sector 3B controller had been operating the position for the previous two and a half hours. He had been busy, but the number of aircraft had reduced in the last 15 minutes. During the last 30 minutes he had answered a number of radio calls from the pilot of a Visual Flight Rules (VFR) flight which was operating outside controlled airspace but in his area of responsibility for a radar advisory service (RAS). RAS had been introduced one month previously, and the sector had almost full radar coverage in non-controlled airspace. Consequently, the sector controllers often had pilots operating on the frequency using RAS procedures. The pilot of the VFR aircraft was incorrectly pre-fixing his radio transmissions with "Brisbane Centre" which required an acknowledgement from the Sector 3B controller. This had been annoying and was frustrating the controller. He had felt relieved when the pilot of the VFR aircraft transferred to an adjacent control position; Sector 3L.

When the crew of the B747SP transmitted to the controller requesting advice of the traffic ahead, the Sector 3B controller had been discussing aspects of the VFR flight with the Sector 3L controller. The Sector 3L controller was providing a RAS in his sector and had queried the Sector 3B controller with respect to the previous transmissions from the pilot of the VFR aircraft. The controllers had not utilised the intercom communications system to discuss the flight but had talked between the two consoles. Consequently, the Sector 3B controller's attention was diverted from his display as the horizontal separation between the B747SP and BA146 approached the minimum required.

After returning his attention to the display, the controller observed that the 5 NM radar separation standard was about to be infringed as the B747SP approached the BA146. The crew of the BA146 were unaware that the B747SP was approaching their aircraft from behind. The Sector 3B controller immediately instructed the crew of the B747SP to turn right in an endeavour to maintain separation between the two aircraft and then advised the crew that the traffic was a BA146. The crew of the B747SP complied with the Sector controller's instructions. The Sector 3B controller instructed the crew of the BA146 to maintain FL230 and then requested the crew of the B747SP to expedite climb until passing FL240. The horizontal separation reduced to 2.7 NM before vertical separation of 1,000 ft was established. There was a breakdown of separation.

ANALYSIS

The Sector 3B controller was relying on maintaining horizontal separation until vertical separation was achieved. The maintenance of adequate horizontal separation was conditional upon the regular scanning of the radar display by the controller. This was especially so because of the significant overtaking groundspeed of the B747SP.

Once the controller elected to monitor the situation instead of using a method of separation assurance, he needed to concentrate more on the radar display. However, he allowed himself to be distracted, firstly by the radio transmissions from the pilot of the VFR aircraft and secondly, by conversing with the adjacent sector controller. His concentration may also have lapsed to some degree because of the reduction in the number of aircraft on frequency in the previous 15 minutes.

Had the aircraft not been fitted with an ACAS, or had the crew not queried the controller, there was the possibility of a collision. Without an ACAS the crew may have observed the BA146 through the aircraft's windscreen; however, this would have been subject to the crew's cockpit workload. Their attention may have been inside the aircraft and consequently they would not have seen the BA146. The operation of the ACAS in the B747SP and the crew's request for traffic information to the controller were active defences in the situation.

SIGNIFICANT FACTORS

1. The Sector 3B controller did not utilise separation assurance techniques.
2. The Sector 3B controller's attention was diverted from monitoring the radar display during a critical phase.
3. The B747SP crew's use of the ACAS and subsequent request for traffic information alerted the controller to the possibility of a breakdown in separation.

A military Hercules (C130) aircraft had departed Richmond, NSW for Canberra, ACT and was initially assigned climb to 6,000 ft by Departures South control (DepS). The intention of the controller was to climb the C130 to be at a level above that required for arriving aircraft to have vacated on descent, by the crossing point of the tracks. Such a climb would have required the C130 to reach 9,000 ft before the respective tracks came into conflict.

A Boeing 747 (B747) was inbound to Sydney, NSW on a flight from Melbourne, Vic. and had been assigned descent to 6,000 ft, via an appropriate standard arrival route, by Approach South control (AppS).

As the two controllers radar vectored their respective aircraft, the Departures North controller (DepN) observed that the aircraft were coming into conflict and alerted both the AppS and DepS controllers. Radar vectors and traffic information were given to the crews of both aircraft, and they passed within 2 NM of each other at the same height. The separation standard is 3 NM in this situation and, therefore, a breakdown of separation occurred.

Sydney airspace is divided into various areas of jurisdiction, and, in this case, AppS had descended the B747 in accordance with this airspace management agreement. However, the controller did not notice that the C130 was at an inappropriate altitude and in his area of responsibility.

The DepS controller had a choice of methods that he could use to separate the C130 from arriving traffic. He could have instructed the C130 to maintain 5,000 ft, i.e. 1,000 ft beneath the allocated arrival altitude, or, as he chose in this case, he could have directed the C130 to climb to an altitude above that required by the arrival procedure.

The workload and complexity of the traffic situation for the DepS controller was high, and although his plan of action was sound, he forgot to instruct the C130 to climb.

SIGNIFICANT FACTORS

1. The workload and complexity of the task of the DepS controller were high.
2. The DepS controller forgot to take the action which would have guaranteed the separation between the B747 and the C130.
3. The AppS controller did not notice that the C130 was at an inappropriate altitude for its track.

During low level stock spotting, the engine of the aircraft developed a miss. The pilot suspected water in the fuel and decided on a precautionary landing. During the landing roll in a paddock, the nose gear struck a small tree stump not seen by the pilot. The aircraft nosed over and came to rest upside down. The pilot was not injured.

The pilot under check had not flown for some 13 years but had resumed flying in early 1996. Prior to the completion of an endorsement on the Piper Arrow aircraft the pilot was required to carry out a load check with another instructor. In addition to the two pilots, two passengers were carried to bring the aircraft weight to near maximum.

The instructor briefed the pilot on the sequences to be flown, which included a glide approach and landing. A number of circuits were conducted initially, including an unsuccessful glide approach. The instructor elected to change the runway direction being used, due to possible adverse effects from the setting sun on the performance of the pilot.

On the next circuit, as the aircraft passed abeam the landing threshold at a height of 1,000 ft, the instructor retarded the throttle to idle. The pilot turned onto base and lowered the landing gear, but by mid-base appeared to be getting too low. The instructor allowed the pilot to continue the approach, but lost sight of the runway due to the position of the sun on base, and the nose attitude of the aircraft. The pilot turned the aircraft onto final at between 100-200 ft, progressively raising the nose in an attempt to reach the threshold, resulting in a decreasing airspeed. The instructor reminded the pilot to monitor the airspeed, which was indicating 50-60 kt just prior to touchdown.

The aircraft touched down heavily in a left wing low attitude, scraping the left wingtip. The aircraft then bounced, before again landing heavily, collapsing the right main landing gear. The aircraft then slid a short distance before coming to rest against an adjacent boundary fence. All four occupants were able to escape without injury.

The pilot reported that the landing gear indication lights showed only two green when the gear was selected down in the circuit at Palmers Island. After checking that the third light bulb was serviceable, he slowed the aircraft on base, and the gear warning horn sounded. The pilot was able to contact the owner of the strip on a mobile phone and explain the situation. He then carried out two missed approaches, and the strip owner advised that the right gear was not locked down and was hanging at a 45-degree angle. The pilot then tried the emergency method to extend the gear, and yawing and positive g manoeuvres, without success. He then decided to return for a landing at Coolangatta where emergency services were available.

On arrival at Coolangatta several more unsuccessful attempts were made to lower the gear by normal and emergency methods. The aircraft was finally landed on runway 14 on the left main and nose gear, with emergency services in attendance.

Post flight examination of the gear actuating ram revealed that paint on the ram had caused a seal to roll up and effectively jammed the actuator.

A Boeing 727 and a Boeing 737 were both on descent to Brisbane from the north. The B727 was ahead of the B737 and was instructed to reduce speed to 230 knots for sequencing. As the speed reduction took effect the following B737 closed rapidly, and the situation was not observed until both aircraft were at flight level 255 and 3.1 nm. Minimum separation is 5 nm. The B737 was turned onto a heading of 180 degrees for avoidance, and there was no further closure.

The traffic situation at the time was light, following a relatively busy period. There was no underlying reason for the controller's failure to maintain the required separation standard. There appears to have been a lapse in concentration following a period of heavy traffic.