On 30 April 2005, the pilot of a Beech Aircraft Corporation V35A Bonanza aircraft, registered VH-FWE, was conducting a private flight from Lilydale, Vic. to Temora, NSW. The pilot reported that while cruising at 7,500 ft, there was a loss of aileron control. Initially the aircraft tended to drift to the right, which he corrected by rolling the aircraft to the left. He then felt something break and the right wing dropped. He turned the aileron control yoke to the left, until it was almost upside down, but the aircraft continued rolling to the right and entered a progressively steeper descent. The pilot broadcast a PAN¹advising air traffic control that he had an aileron control problem and that he would attempt to land the aircraft on a local glider field. He reported that he arrested the roll by extending the landing gear, adjusting engine power and applying full left rudder. The pilot subsequently landed the aircraft without the use of wing flaps.

Aircraft

The aircraft was manufactured in 1969 and had recorded 6,154.8 hours in service at the time of the incident. It was maintained in accordance with the applicable maintenance requirements and had a valid Maintenance Release. It had flown approximately 22.9 hours since the last periodic inspection completed in March 2005.

Aileron control examination

When examined, the aircraft's left aileron was found deflected to the fully down position and the right aileron fully up. To return the ailerons to their neutral position, a force was required to overcome the tension of the rudder interconnect bungee spring. Once the force was removed, both ailerons returned to the fully deflected positions. The examination of the aileron control cables revealed that the right aileron 'up' cable terminal, located in the rear spar carry through structure, had failed.

The aircraft manufacturer advised that since the aileron control cables are connected to the rudder interconnect bungee spring, the separation of the right aileron up cable would result in that spring forcing the left aileron down and the right aileron up (Figure 1).

Figure 1: Aileron control system

Terminal examination

The failed control cable terminal was sent to the Australian Transport Safety Bureau (ATSB) for examination. The terminal shaft that is screwed into the turnbuckle had fractured close to the locking wire attachment point (Figure 2). The examination revealed that the fracture was initiated by stress corrosion cracking² that had propagated under the surface of the shaft and weakened it to the point of failure.

Figure 2: Failed control cable terminal

The cable terminal was a standard swaged fitting designated AN669. Chemical analysis of the material showed that its composition closely matched that of SAE-AISI 303 stainless steel. A recent US National Transportation Safety Board (NTSB) Safety Recommendation³ identified SAE-AISI 303 stainless steel as being susceptible to stress corrosion cracking when used in a corrosive environment. The Safety Recommendation mentioned that cracking propagates as a function of the time a component is exposed to the corrosive environment rather than its actual time in service and that 'about 18 to 20 years is required for terminals exposed to the most damaging environment to reach their fracture point'.

Terminal inspection

During routine aircraft maintenance inspection of control system cables, corrosion pits on the surface of the cable terminal shaft may be the only visual indication of a potential problem. With the shaft area being typically wrapped with safety wire, the shaft can be difficult to inspect.

In August 2001, The Civil Aviation Safety Authority (CASA) issued Airworthiness Bulletin 27-1 Issue 1, Control Cable Terminal Inspection that was also published on the CASA web site www.casa.gov.au. The Airworthiness Bulletin provided information regarding the susceptibility of control cable terminals made of SAE-AISI 303 stainless steel to failure due to stress corrosion and highlighted the 'importance of meticulous inspection of the terminals'. It recommended that aircraft older than 15 years, and using terminals constructed of SAE-AISI 303 stainless steel, should have their control cable terminals visually inspected on an annual basis.

A review of the aircraft's logbooks found no evidence of the aileron controls having been subjected to any specific inspections to detect corrosion, including the removal of lock wire, within the previous 15 years. Routine maintenance inspections had been conducted during that period.

Both the ATSB and CASA databases contained four reports of similar control cable terminal failures in the period between 1995 and 2004. The NTSB Safety Recommendation mentioned 10 instances of aircraft that were found having fractured or cracked control cable terminals.

1. PAN is a radio code indicating uncertainty or alert.
2. A cracking process that requires the simultaneous action of a corrosive environment, such as a chlorine-rich atmosphere in moist coastal areas, and sustained tensile stress.
3. US National Transportation Safety Board Safety Recommendation A-01-6 through -8 of April 16, 2001.

The Australian Transport Safety Bureau did not conduct an on-site investigation of this occurrence.

A Beech V35A Bonanza sustained a loss of aileron control while cruising at 7,500 ft. The pilot reported turning the aileron control yoke to the left, but the aircraft continued rolling to the right and entered into a progressively steeper descent. He arrested the roll by extending the landing gear, adjusting engine power and applying full rudder.

At 0803 Western Standard Time on 24 April 2005, an Airbus Industrie A340-212 (Airbus) aircraft, registered ZS-SLA, with a crew of 11 and 219 passengers, landed short of the displaced threshold on runway 21 at Perth Airport, Western Australia. The aircraft was on a scheduled flight from Johannesburg, South Africa. The pilot in command was the handling pilot for the approach and landing at Perth.

ANALYSIS

The final minutes of the recorded Air Traffic Services radar data indicated that the pilot performed a series of turns in a constant descent that was consistent with a forced landing. Given the pilot's history of performing many practice forced landings, it is likely that immediately prior to the accident, the pilot was conducting a practice forced landing.

When radar contact was lost, the aircraft was already below the minimum altitude for a practiced forced landing and there was no indication that the pilot had decreased the rate of descent. That was confirmed by witnesses that indicated that the aircraft was well below 500 ft above ground level.

Based on the pilot's training records and interviews with flight instructors, it is probable that the pilot was fixated on the chosen landing area and descended below the minimum height for a go-around. During the latter stages of the approach recorded by the radar, the pilot performed a tight 360º turn. That may have been intentional to allow the aircraft to lose height and still be positioned for the selected landing area. During the turn, the aircraft lost approximately 25 kts, which reduced the margin above the aircraft's stall speed.

A person near the accident site reported seeing the aircraft at a very low altitude and flying quietly before hearing power applied. However, the atmospheric conditions around the time of the accident were conducive to the formation of serious carburettor ice at descent power and the engine may not have been capable of producing full power when it was applied. Because the person's attention returned to their duties, it was not known if the application of power that they reported was sustained for any length of time. The evidence in the wreckage indicated that there was little or no power applied at impact. The pilot may have removed power as part of the stall recovery procedure. The use of carburettor heat could not be determined and the formation of carburettor ice was a possibility.

The attitude at which the aircraft impacted the ground and the damage to the tail section indicated that the aircraft had stalled before it impacted the ground. The combination of the loss of airspeed during the turn and the pilot's documented difficulty with stall recognition and response, may have led to an inadvertent stall, either during the go-around or in the subsequent climb out. The height at which the aircraft stalled was not sufficient to permit a recovery. It was not possible to determine if carburettor icing had reduced the power available for the go-around and aggravated the situation.

Fatigue

Based on the pilot's activities and sleep patterns prior to the occurrence, it was apparent that the pilot probably obtained only 5 to 6 hours of interrupted sleep on the night before the accident. Even though this was consistent with his normal sleeping patterns, in all likelihood, the pilot may have started the day with a degree of fatigue as a result of insufficient quantity and quality of sleep the previous night. The pilot may have also been experiencing the effects of chronic fatigue given his recurring pattern of interrupted and relatively low quantity of sleep. Consequently, fatigue may have reduced the pilot's ability to fly the aircraft accurately and to develop and maintain awareness of, and make timely decisions in response to, a degraded aircraft state, such as a stall.

Pilot's training history

The pilot had required a significant amount of flying training to meet the General Flying Progress Test standard. The pilot's training was regular, but spread over a considerable period of time. The training records indicated that the pilot had difficulty in acquiring, maintaining and consolidating the skills required to safely operate a light aircraft. Many lessons were repeated to bring the pilot up to the required competency standard. Of particular note is that the pilot consistently demonstrated poor airspeed control during practice forced landings, indecision, a poor awareness of an impending stall, a lack of response to the stall warning horn, and incorrect stall recovery technique. These factors are consistent with the circumstances surrounding the accident.

FACTUAL INFORMATION¹

History of the flight

At about 0945 Eastern Standard Time² on Saturday 23 April 2005, a Cessna Aircraft Company A150L Aerobat aircraft, registered VH-UPS, departed Coldstream Airfield, Vic. for a private flight in the Coldstream General Flying Training Area, with the pilot as the only occupant (Figure 1).

The aircraft was first tracked by the Air Traffic Services (ATS) radar at 0949 heading in a northerly direction consistent with a departure from Coldstream runway 35. Over the next 6 to 7 minutes, the aircraft made a series of right turns that brought the aircraft into an area to the southeast of Steel Hill. The radar track shows the aircraft performing some aerial manoeuvres in this area before heading north-northeast towards Healesville for several minutes, then turning left for another series of aerial manoeuvres.

The final minutes of recorded radar data (Figure 2) show that the aircraft performed a descending orbit into the Yarra Valley before losing radar contact. The aircraft did not reappear on radar. At about that time, a passenger in a vehicle travelling along the Healesville - Koo Wee Rup Road observed the aircraft flying at low level. Shortly after, the aircraft was seen in a steep dive before it disappeared behind an embankment. The occupants of the vehicle located the wreckage of the aircraft in an open field about 1 km west of the Healesville - Koo Wee Rup Road. The aircraft was destroyed by impact forces and the pilot was fatally injured. There was no fire.

Figure1 : Accident location

Figure 2 : Recorded radar track

Recorded radar data showed that the aircraft maintained a fairly constant rate of descent of about 660 ft/min from an altitude of about 2,400 ft Above Mean Sea Level (AMSL), down to about 700 ft AMSL. That placed the aircraft at about 430 ft above ground level (AGL) when radar contact was lost. There was no indication in the radar data that the aircraft had ceased its descent when contact was lost. The accident site was located about 0.7 NM to the north of the last radar return.

At about 1,000 feet AMSL and heading in a north-easterly direction, the aircraft performed a tight 360º turn³ whilst maintaining the descent. During this turn, the radar recorded a decrease in speed of about 25 kts.

An employee working on the property where the accident occurred observed the aircraft pass at a very low level (estimated between 100 and 200 ft AGL) and flying quietly. The aircraft passed within several hundred metres of the employee and was headed in a northerly direction. The employee reported hearing the engine sound increase before returning their attention to their duties. Having worked on the property for some years, and observed many aircraft training in the area, the employee did not notice anything unusual about the aircraft, other than it being very low. Although located only 900 m from the accident site, the employee did not observe the final moments of the flight or the collision with the ground.

Wreckage information

Ground marks and crushing of the left-wing tip indicated that the aircraft had impacted the ground in a left wing-low and approximately 30º nose-down attitude. The direction of flight was approximately 320º (magnetic). The wing flaps were found in the fully retracted position.

The aircraft came to rest about 10 m from the impact point (Figure 3). The fuselage lay on its roof with the left wing wrapped over the cabin and the right wing in a near vertical position. The rear fuselage was bent downward and to the left. The tailplane had separated from the fuselage and the fin, which was lying on the right tailplane, had broken away from its mounting brackets. There were no indications of any pre-existing defects in the aircraft structure.

Figure 3 : Aircraft wreckage

Examination of the propeller, throttle lever position and engine instruments indicated that the engine was operating at low RPM and developing little or no significant engine power at impact. Examination of the engine found no evidence of a mechanical or system failure that would have prevented the production of power prior to impact. Due to the impact damage, the status of the carburettor heat control at impact could not be reliably determined.

Examination of the stall warning system, airspeed indicator and altimeter indicated that they were capable of normal operation during the flight prior to impact.
 

Personnel information

The pilot's flying experience was estimated as:

The pilot commenced part-time flying training on 23 May 2003 and was issued a Student Pilot Licence on 15 November 2003. The pilot's first solo flight on 23 November 2003 was made after receiving 43.7 hours of dual training. A pre-licence check flight was conducted by a senior instructor on 6 January 2004 when the pilot had 77.3 hours of experience. However, it was not until 24 July 2004 that the pilot achieved the General Flying Progress Test (GFPT) after a further 51 hours of flying training. At that time, the pilot had accumulated a total flying time of 128.4 hours, of which 104.9 hours were dual instruction. All of the pilot's flying training was undertaken at the same organisation.

The flying training organisation's pre-GFPT syllabus indicated that the minimum flying training required to the end of the GFPT phase was 23 hours dual and 6 hours solo, a total of 29 hours. The regulatory minimum total flight time required before attempting the GFPT was 20 hours of flight time.

After completing the GFPT, the pilot commenced cross-country navigation training as part of the Private Pilot (Aeroplane) Licence training syllabus. He had also completed 9.7 hours of aerobatic flight training but had not received an aerobatics endorsement. Entries in the pilot's logbook suggested that the pilot had previously engaged in solo aerobatics with a passenger on board the aircraft.

The pilot held a current Class 2 medical certificate that was endorsed with the restriction 'Renew by CASA only'. The results of the post-mortem examination and toxicology screening found no evidence of any physiological factor that may have impaired the pilot's performance during the accident flight.

In the days leading up to the accident flight, the pilot averaged 5 to 6 hours of sleep per night. These sleep periods were interrupted by waking periods late at night and was reported as the pilot's typical sleep pattern.

A review of the pilot's training records indicated that many lessons were repeated before the minimum competency standards were met. The pilot had recurring difficulties in airspeed management, steep and tight turns, identification of impending stall, response to the stall warning horn, recovery from the stall and go-around decision and technique. The pilot's instructors noted that constant reminders to monitor airspeed and altitude and to perform the appropriate recovery technique were required. The training records included several entries relating to inattention, tunnel vision and trouble attending to all parameters. Annotations of these difficulties were associated with many aspects of the pilot's training, but were particularly apparent for practiced forced landings.

The pilot had recorded a large number of practice forced landings during training, the majority of which were with an instructor.

Practice forced landing

The practice forced landing manoeuvre, as used in the flying training organisation's syllabus, typically involved simulating an engine failure by closing the throttle and gliding the aircraft toward a selected landing area.

The main objective of the manoeuvre was to develop judgement and skill in positioning the aircraft for a gliding approach to the selected field. When the manoeuvre is practiced on to an airfield, a landing is made off the approach. However, when the manoeuvre is practiced in the training area, the student is required to demonstrate a go-around from a safe height, usually not below 500 ft AGL. The go-around manoeuvre requires the pilot to apply full power and select the carburettor heat off, raise the flaps (if used) and establish the normal climb. If, for any reason, engine power is not available, the aircraft is ideally positioned for an emergency landing into the selected field.

To prevent the formation of carburettor ice during the practice forced landing, full carburettor heat is applied. A short application of engine power is normally made every 1,000 ft of descent to maintain engine temperatures. If carburettor heat is not selected off during the go-around, full power will not be available. When the normal climb attitude is maintained with less than full power, the aircraft will climb at a slower airspeed and rate of climb.

Aircraft information

The Cessna A150L aircraft was a two-place, high-wing, light aircraft designed for general flying training, but was also capable of aerobatic flight. The aircraft was powered by a Teledyne-Continental Motors O-200-A normally-aspirated piston engine through a fixed-pitch two-bladed propeller.

VH-UPS was imported into Australia in 1990 and had been operated and maintained by the same flying club since that time. It was utilised for both initial flying training and aerobatic training.

The flying club maintained the aircraft in accordance with a CASA approved maintenance system. The last periodic maintenance inspection was carried out on 23 March 2005. The aircraft's maintenance release, recovered from the wreckage, did not list any defects, and the documentation indicated that all required maintenance was completed. The maintenance release was endorsed by a licensed pilot certifying that the daily inspection had been satisfactorily completed on the morning of the accident. The accident flight was the first flight of the day for the aircraft.

Prior to importation into Australia, the aircraft had been fitted with a carburettor ice detection system in accordance with a United States Federal Aviation Administration approved kit. The system consisted of an optical sensor in the carburettor, a control box and a warning light mounted on the instrument panel. The operating instructions indicated that the pilot was required to adjust the sensitivity of the system to suit the local conditions prior to operation. The operational status of the system at the time of the accident could not be determined.

The aircraft had sufficient fuel and was within the weight and centre of gravity limitations for the duration of the flight.

Meteorological information

The Bureau of Meteorology automatic weather station for Coldstream recorded the environmental conditions for Saturday 23 April 2005 as:

The skies were overcast with high level cloud, there was a degree of haze; however, the horizon in the valley was clearly distinguishable. People in the area reported that winds were very light.

Carburettor icing

On the day of the accident, the atmospheric conditions were conducive to the formation of serious carburettor icing at descent power. Refer to Appendix A for a Flight Safety Australia magazine ⁵ article on carburettor icing.

1. Only those investigation areas identified by the headings and subheadings were considered to be relevant to the circumstances of the occurrence.
2. Eastern Standard Time was Coordinated Universal Time (UTC) + 10 hours.
3. The large changes in the aircraft position in this region are likely due to limitations in the radar system at low altitude, however the general pattern of a tight turn is indicated by the data points at 1106, 1006, 906 and 806 ft.
4. Total time in service.
5. Flight Safety Australia magazine is a publication of the Australian Civil Aviation Safety Authority.

At about 0945 Eastern Standard Time on Saturday 23 April 2005, a Cessna Aircraft Company A150L Aerobat aircraft, registered VH-UPS, departed Coldstream Airfield, Vic, for a private flight in the Coldstream General Flying Training Area, with the pilot as the only occupant.

The aircraft was tracked by the Air Traffic Services radar after its departure from Coldstream Airfield. The radar track showed that the aircraft performed some aerial manoeuvres to the east of the airfield before a descending orbit into the Yarra Valley when radar contact was lost. At about that time a passenger in a vehicle travelling along the Healesville - Koo Wee Rup Road observed the aircraft flying at low level. Shortly after, the aircraft was seen in a steep dive before they lost sight of it. The occupants of the vehicle located the wreckage of the aircraft in an open field about 1 km west of the Healesville - Koo Wee Rup Road. The aircraft was destroyed by impact forces and the pilot was fatally injured.

The aircraft had impacted the ground in a left wing-low and nose-down attitude. The fuselage lay on its roof with the left wing wrapped over the cabin and the right wing in a near vertical position. The rear fuselage was bent downward and to the left. The tailplane had separated from the fuselage and the fin had broken away from its mounting brackets. There were no indications of a pre-existing defect in the structure.

The investigation found that it was likely that the pilot was performing a practice forced landing and had descended below the safe altitude when the accident occurred. The airspeed was reduced to a point that the aircraft stalled and the altitude was not sufficient to affect a recovery before impact with the ground. It is possible that carburettor ice was present during the descent.

Related link: 

In this occurrence, the controller did not perceive the potential conflict between the aircraft, despite previous refresher training that should have assisted in the task.

Although the presence of the supervisor in the operations room created an opportunity to discuss an operational issue, it was not a priority. The controller should have discussed the issue at some other time when he was not responsible for an operational position. The supervisor was also in a position to defer the discussion with the controller, until a more suitable time or location, which would have reduced the likelihood of compromising operations.

While distraction could not be discounted as a contributing factor, the circumstances of the occurrence are consistent with the findings of the Airservices Australia June 2003 review, particularly with respect to low levels of situational awareness by controllers. Over time, the benefits of the implementation of the review recommendations in helping to develop controller awareness of potential performance limitations should become apparent.

ANALYSIS

Introduction

Although there was no specified minimum distance standard for visual separation in these circumstances, the aerodrome controller was unable to continue to apply a visual separation standard, in azimuth, between the 737 and the Aero Commander. This analysis examines the development of the occurrence and highlights the safety issues that became evident as a result of the investigation.

Noise abatement procedures

Airspace restrictions imposed by the noise abatement procedures in force at the time of the occurrence resulted in limited options available to either the aerodrome controller or the approach controller to separate the departing Aero Commander with the inbound aircraft. The approach controller determined that he would be unable to establish and maintain a separation standard between the two aircraft and comply with noise abatement procedures, and so relied on the aerodrome controller to separate the two aircraft using visual separation.

The requirement for pilots to request a start clearance would normally provide the aerodrome controller with an opportunity to assess the traffic situation, in light of airspace limitations associated with noise abatement procedures, so that any delays can be absorbed prior to the aircraft's engines being started. A heading of 360 degrees was an appropriate heading in the circumstances. It would also have complied with noise abatement procedures and facilitated the application of visual separation in azimuth.

Controllers cannot be held responsible for delays to departing aircraft as a result of noise abatement procedures. Controllers are required to take such restrictions into account in their normal decision-making processes. The noise abatement procedures themselves were not considered to have contributed significantly to this occurrence.

Air traffic control separation standards and procedures

The converging tracks of the two aircraft precluded the aerodrome controller from ensuring that visual separation, in azimuth, was not infringed.

The low light conditions at that time of day and the cloud cover, may have made it difficult for the aerodrome controller to visually determine the departure track of the Aero Commander. Reference to the tower radar display was authorised by the Manual of Air Traffic Services (MATS) and would have clearly indicated the Aero Commander's track. Had the aerodrome controller referred to the tower radar display earlier, he may have been able to take action in sufficient time to ensure that separation was not infringed.

The situation which arose, where the aerodrome controller was separating the aircraft while the aircraft were not on the aerodrome control frequency, was not consistent with the letter of agreement. However, it did enable the approach controller to provide mutual traffic information to the pilots of both aircraft. That increased the awareness of the 737 crew of the presence of the Aero Commander and assisted the pilot of the Aero Commander to see the 737.

Although it would have been difficult for the aerodrome controller to separate the departing Aero Commander on a heading of 090 degrees, with arriving aircraft on the final approach path for runway 19, the aerodrome controller accepted those instructions and confirmed that he could separate in those circumstances. On that basis, the approach controller authorised the departure. The approach controller coordinated the departure instructions with the aerodrome controller in accordance with the letter of agreement. The approach controller confirmed, on a number of occasions, that the aerodrome controller had accepted responsibility for separating the Aero Commander on a heading of 090 degrees. The approach controller had no way of knowing that the aerodrome controller had misunderstood the instruction.

From the aerodrome controller's perspective, a heading of 360 degrees off runway 32 was appropriate given the disposition of the arriving aircraft. It would also have complied with the noise abatement procedures and enabled him to visually separate the Aero Commander in azimuth with the 737, once the 737 was established on the final approach path.

The aerodrome controller's subsequent request for a 20 degree left turn for the Aero Commander is difficult to reconcile. The resultant heading of 070 degrees turned the Aero Commander towards the 737 and does not appear to be consistent with a resolution of the developing confliction. By that time the aerodrome controller could not have been certain from visual observation that the aircraft were not in close proximity.

The investigation was unable to determine why the aerodrome controller had a 'mindset' that the Aero Commander was departing on a heading of 360 degrees, when that option was never discussed or coordinated with the approach controller. The higher workload that was reported to have resulted from The Australian Advanced Air Traffic System data upgrade may have had an adverse effect on the aerodrome controller's cognitive processes towards the end of the night shift. The possibility that fatigue contributed to the occurrence could not be discounted.

Sequence of events

On 14 April 2005, an Aero Commander 500-S aircraft, registered VH-YJR, departed Brisbane aerodrome on a non-scheduled flight to Maryborough, Qld. It passed within 1 NM horizontally and 500 ft vertically of a Boeing Company 737-76Q (737) aircraft, registered VH-VBU, that was inbound from Darwin, NT, on a scheduled passenger service.

The Aero Commander became airborne off runway 32 at 0543 Eastern Standard Time, 4 minutes after the nominated first light for Brisbane aerodrome. The Brisbane aerodrome controller had instructed the pilot of the Aero Commander to turn right, once airborne, onto a heading of 090 degrees and to climb to 2,000 ft. The pilot complied with the departure instructions and contacted the approach controller on the approach frequency. The approach controller acknowledged that broadcast and asked the pilot for 'good forward speed'.

The crew of the 737 were on the approach frequency and were positioning the aircraft for final approach to runway 19. Although the pilot of the Aero Commander and the crew of the 737 were on the approach frequency, the aerodrome controller confirmed with the approach controller that he was visually separating both aircraft as had been previously agreed. The aerodrome controller later reported that he was expecting the approach controller to assign a heading of 360 degrees to the pilot of the Aero Commander.

The approach controller passed traffic information to the pilots of both aircraft and the Aero Commander pilot sighted the 737 soon after. At 0544:20 the crew of the 737 reported that they were established on the final approach path for runway 19. The approach controller advised them that the Aero Commander was going to cross the runway 19 final approach path and that the tower was providing visual separation.

The aerodrome controller became concerned about the separation between the two aircraft and at 0544:50 asked the approach controller to instruct the pilot of the Aero Commander to turn left 20 degrees. That instruction was passed and the Aero Commander pilot complied. The aerodrome controller was still concerned and asked the approach controller to instruct the pilot of the Aero Commander to make an immediate hard left turn onto a heading of 360 degrees. The approach controller advised the aerodrome controller that he was concerned about that heading and did not transmit the instruction.

By 0545:26 the aerodrome controller considered that the Aero Commander had crossed the runway 19 final approach path. In response to a request by the approach controller, the pilot of the Aero Commander confirmed that he could see the 737, but at that stage the 737 crew had not seen the Aero Commander. Not long after that, the 737 crew saw the Aero Commander and were subsequently transferred to the Brisbane tower frequency. Figure 1 shows the position of the two aircraft as the Aero Commander crossed the final approach path at 0545:30.

Figure 1: Relative flight paths of the Aero Commander and the 737 as the Aero Commander crossed the final approach path of runway 19 at 05:45:30

A review of the recorded radar data showed that separation between the aircraft reduced to a minimum of 0.95 NM horizontally, at which time vertical separation had reduced to 500 ft.

Noise abatement procedures

The noise abatement procedures applicable at Brisbane at the time of the occurrence specified that all aircraft departing runway 32 between 2200 and 0600 must be contained within a sector of airspace between 360 and 120 degrees, over water, until leaving 5,000 ft. A heading of 360 degrees for a departure from runway 32 would have complied with those requirements.

To comply with the noise abatement procedures, runway 19 was the nominated duty runway for arrivals, and runway 01 was the nominated duty runway for departures. Pilots were also advised, on the automatic terminal information service, to obtain approval from air traffic control prior to starting engines. The requirement for a start clearance in thesecircumstances was in accordance with the Manual of Air Traffic Services (MATS) and enabled any delays to be absorbed on the ground before an aircraft's engines were started.

The aerodrome controller issued a start clearance to the pilot of the Aero Commander. The aerodrome controller did not coordinate the start clearance with the approach controller, nor was he required to do so. The ADC was required to review the disposition of inbound traffic when making a decision as to the timing of a start clearance.

The approach controller reported that he instructed the aerodrome controller to assign a departure heading of 090 to the pilot of the Aero Commander to ensure compliance with the noise abatement procedures.

Air traffic control separation standards and procedures

Control of aircraft in the Brisbane aerodrome terminal area was provided by an aerodrome controller located in the control tower using visual procedures, or by an approach controller using radar information. The MATS stated that the primary role of aerodrome controllers was to maintain visual observation of aircraft operations. Coordination of responsibilities and roles was required between the aerodrome controller and the approach controller, and formal guidelines were specified in a letter of agreement. The letter of agreement stated in part that:

In visual conditions, separation is achieved by the application of a radar standard or the provision of visual separation.

It also stated that:

In the application of visual separation, BNT [Brisbane aerodrome controller] shall ensure that separation in azimuth ¹ is maintained until the establishment of a radar or procedural separation standard … In all situations where BNT is providing visual separation, traffic that will operate in close proximity will be retained on TWR [tower] frequency.

Although the aerodrome controller transferred the pilot of the Aero Commander to the departures frequency, the approach controller did not accept separation responsibility for the aircraft after the 737 was established on the runway 19 final approach path. He reported that he may not have been able to maintain the minimum radar separation standard of 3 NM horizontally, or 1,000 ft vertically.

The aerodrome controller reported that he accepted responsibility for visual separation between the two aircraft once the 737 was established on the runway 19 final approach path, because he had a 'mindset' that the Aero Commander was going to turn right onto a heading of 360 degrees once airborne. The aerodrome controller later reported that he would not have accepted responsibility for separation if he had realised that the approach controller had assigned a heading of 090 degrees, because that heading would not have enabled him to maintain visual separation between the two aircraft. Although the pilot of the Aero Commander advised the approach controller that he had the 737 in sight, the approach controller did not assign responsibility for separation to the pilot of the Aero Commander. There was an infringement of separation standards.

The information in the letter of agreement was supported by the Manual of Air Traffic Services (MATS), which contained procedures to be used by air traffic controllers. Paragraph 4.5.2.8 (effective 10 June 2004) stated that:

In providing visual separation, controllers should rely primarily on azimuth. Visual separation by judgement of relative distance or height shall be used only with such wide margins that there is no possibility of the aircraft being in close proximity.

The Brisbane tower was equipped with a radar display that provided the aerodrome controller with the same traffic display that was provided to the approach controller. The MATS addressed the use of tower radar in an aerodrome control service. It stated that the tower radar display was available for the determination of the altitude, position, or tracking of aircraft to establish or monitor separation. However, the MATS also stated that:

…the use of Tower radar should not impinge upon an aerodrome controller's primary function of maintaining a visual observation of operations on and in the vicinity of the aerodrome.

The MATS also stated that separation assurance could be achieved through planning traffic to ensure separation, executing the plan to achieve separation and monitoring the situation to ensure that the plan and the execution are effective.

Aerodrome controller

The aerodrome controller was trained and rated for the aerodrome control function at Brisbane. At the time of the occurrence he was nearing the end of a night shift which had commenced at 2200 the previous day. He reported that there had been a data upgrade to The Australian Advanced Air Traffic System during the night. The aerodrome controller considered that the data upgrade resulted in a higher workload than a standard night shift.

The aerodrome controller reported that, at the time of the occurrence, he felt fatigued. He also reported that he was feeling slightly unwell, but that he considered himself fit for duty. He was sleeping adequately and, apart from the slight illness, there were no indications of any personal, physiological or medical issues that were likely to have influenced the controller's performance.

Meteorological information

The weather information being broadcast to pilots for Brisbane Airport at the time of the occurrence advised that the visibility was greater than 10 km, that there were showers in the area and some cloud at 2,500 ft. The wind was reported as 180 degrees at 8 kts, with a maximum downwind of 10 kts on runway 01.

1. Horizontal bearing or direction.

On 14 April 2005, an Aero Commander 500-S aircraft, registered VH-YJR, departed Brisbane aerodrome on a non-scheduled flight to Maryborough, Qld. It passed within 1 NM horizontally and 500 ft vertically of a Boeing Company 737-76Q (737) aircraft, registered VH-VBU, that was inbound from Darwin, NT, on a scheduled passenger service.