1. FACTUAL INFORMATION

1.1 The incident

The Airbus A300-B4 aircraft departed Sydney on a scheduled service to Brisbane. At about 700 ft after take-off the left engine fire warning activated. The crew carried out the appropriate procedures and shut down the left engine. With the engine shut down the fire warning indications ceased, therefore the fire bottle was not discharged. The aircraft was vectored for a priority landing back onto the departure runway and, after ground inspections confirmed the absence of fire, the aircraft was taxied to the terminal for a normal disembarkation.

Inspection of the engine disclosed a rupture of the 14th stage lower bleed air duct. Secondary thermal damage had occurred to the reverser cowl and minor mechanical damage was evident to the reverser mechanism.

1.2. Duct cracking

The engine manufacturer, General Electric (GE), advised that cracking can occur in the lower bleed air duct due to differences in thermal gradients. This occurs because the duct is made from a nickel alloy Inconel 625, and the support link assemblies are made of 321 stainless steel. Thermal stresses occur when the bleed air valve is closed resulting in the lower duct being cooler than the engine case. Installation stresses can also result in cracking.

1.3. Duct examination

The duct is a 90 mm pipe spanning approximately one-third of the circumference of the engine core. Three mounting lugs are welded to the outside surface of the pipe. The duct had ruptured around the toe of the weld at the lap joint of an end lug. Cracking was also present along the toe weld of the other end lug.

The fracture surfaces were subjected to both low power and scanning electron beam microscopy which revealed that the failure was typical of that due to fatigue. The fatigue had multiple initiations along both the outside and inside surfaces of the duct; however, the majority of the fracture had propagated from the outside surface. The fatigue fracture consisted of very fine evenly spaced fatigue striations typical of a constant amplitude load from the stresses associated with thermal cycles.

The fatigue extended around the end of the weld lap joint and approximately 30 mm each side of the lap joint before rapid tearing commenced. The fatigue fracture was stained indicating that hot air had been escaping for some time.

1.4 Propagation rate

The fatigue striation spacing was measured on a small area of fatigue fracture at various distances across the duct section from an origin on the outside surface to the boundary line between two areas of fatigue. From these measurements it was estimated that approximately 2,000 fatigue striations were present on this small area of fatigue fracture. Assuming that a thermal cycle is equivalent to an engine cycle, it would appear that this small area of fatigue had been propagating for 2,000 engine cycles. However, the entire fatigue fracture consisted of many fatigue cracks initiating at different stages during the life of the duct. This indicates that the fatigue cracking had been propagating for in excess of 2,000 engine cycles.

1.5 Recent inspections

The last maintenance inspection was during a Check "A" inspection carried out at 199 hours and 180 cycles prior to failure of the duct.  The last shop visit was 922 hours and 816 cycles prior to failure. The fatigue cracks were present, but not detected, when these inspections were carried out.

1.6 Operator's inspection requirements

The operator's inspection requirement was detailed on Task Card AB3-723300-0801-TN-L and R.  This task card is called up at each Check "A" inspection which at the time of the incident was on a rotating 320/480 hour schedule. The task was originally created on 29 October 1987. The task card in use during the last inspection of the duct was issued with an amendment dated 6 September 1990 which required:

"Visual inspection of high-pressure compressor emphasising......14th stage bleed air manifold for cracks".

This visual inspection was carried out at the last inspection but failed to detect the cracking.

1.7 Manufacturer’s requirement

GE issued Service Bulletin CF6-50-75-064 (SB 064) on 3 August 1990 to institute a recurring inspection aimed at detecting cracks in the 14th stage bleed air ducts.

On Page 4 of SB 064, at item 2.B was a requirement that a Spot Fluorescent Penetrant Inspection (SFPI) technique be used to detect cracks, with a requirement that the SFPI be carried out every 500 flight hours or 150 engine cycles whichever occurs last.

The operator's maintenance system is detailed in the Maintenance Instruction Manual (MIM). This manual sets out the procedures to be used to ensure compliance with the statutory requirements pertaining to engineering and maintenance activities.

Revisions to the MIM are accomplished by entering the necessary details onto a Manual Revision Authority form. The form is then processed in accordance with flow charts contained in the MIM. Some procedures are also contained within instructions raised within specific sections.

The preparation of the Manual Revision Authority form, the routeing through actioning sections, and the subsequent approval and incorporation of an amendment is accomplished by individuals actioning computer-based commands.

1.8 Operator's action

The operator received information, known generically as service literature, regarding introduction of the SFPI technique from both GE and Airbus Industrie (AI), the aircraft manufacturer.

Within the operator's maintenance organisation there are two sections which are required to process changes to maintenance requirements for engines. These are the Power Plant Engineering (PPE) section and the Maintenance Development (MD) section. There were at least four occasions when either or both sections assessed or reviewed the requirements of the SB.

These were:

(a) at initial issue of SB 064,

(b) on receipt of GE Commercial Engine Service Memorandum 76 (CESM 76)

(c) on receipt of an amendment to Airbus Industrie Maintenance Planning Document (MPD) dated October 1991.

(d) on receipt of an MPD amendment dated October 1992

1.9 Initial assessment of SB 064

GE issued SB 064 on 30 August 1990. Contrary to MIM requirements there were no entries made into the computer system that would have allowed the investigation to accurately track the initial routeing of SB 064.

The SB should have been received by PPE and passed to MD for assessment. The PPE engineer involved was no longer employed by the operator at the time of this investigation and was unable to be interviewed regarding his memory of his handling of the SB.

Available records do show that on 28 August 1990 an engineer in MD raised a Manual Revision Authority, numbered AB3100190, requesting the following change to the Maintenance Instruction Manual (MIM):

"Revise tasks AB3-723300-0801-TN-L & R to add visual inspections of the 8th and 14th stage bleed air manifolds". (BASI note - the terms manifold and duct are interchangeable).

The Purpose/Justification part of the Authority stated:

"New General Electric requirement as per SB 75-064".

This request for an MIM change was presented to, and authorised by, the Engineering Manager who did not identify that the assessing engineer in MD had made an incorrect assessment of the inspection process called up in the SB. As a result of the Engineering Manager's authorisation, the task card was amended on 6 September 1990.

MD also raised a Engineering Instruction (EI) numbered EI AB3-075-0102R00. The purpose of the EI is to notify other action sections of any change that may require their attention. This EI was not actioned because the assessing engineer, having raised the Manual Revision Authority, annotated on the EI that the SB was actioned by stating that the EI was "Terminated.... Covered By Maintenance A Checks".  There was no evidence of any communication taking place between PPE and MD prior to the decision to terminate the EI. However, anecdotal evidence suggests that there was often verbal communication between the sections regarding the processing of service literature.

The MIM did not require that a comparison between the SB inspection requirements and those contained in the Maintenance Check A been carried out prior to terminating the EI.

The MIM requires that PPE issue an Action Advice to notify MD that the intent of the SB is to be included in the applicable aircraft checks. An Action Advice covering the initial assessment of SB 064 could not be located.

1.10 General Electric Service Memorandum

On 10 September 1990 GE issued Revision 6 to Commercial Engine Service Memorandum (CESM) No. 76 which contained a consolidated listing of all scheduled inspection and servicing intervals for engines. This was received by PPE on 18 October 1990. PPE raised Action Advice number 9043002 on 1 November 1990 to notify MD of receipt of the CESM. MD assessed and cleared this Action Advice stating it was "Covered by AB3 MPD Revision".

While the statement is correct in that the task cards had been revised, the incorrect assessment and subsequent incorrect procedure were not identified by the person in MD responsible for carrying out the assessment of CESM No. 76.

1.11 AI MPD amendment dated October 1991

Airbus Industrie first introduced the requirement to comply with GE SB 064 via an amendment to the MPD issued in October 1991. The revised MPD was received by MD and assessed. The assessing/action engineer, while noting that GE SB 064 had been incorporated into the MIM via the task cards, did not identify that the original assessment had resulted in an incorrect procedure being called up.

1.12 AI MPD amendment dated October 1992

AI introduced a revision to the inspection intervals for GE SB 064 via a revision to the MPD issued on 30 October 1992.  Again, the MD assessing/action engineer while amending the inspection period did not identify that an incorrect procedure had been called up.

1.13 Operator’s review

When the MIM listing of an incorrect maintenance procedure became apparent the operator immediately established a review of the MIM amendment system. That review examined the procedures in use and checked that all mandatory inspections were correctly specified in the MIM.

The review found that:

(a) action Advice procedures were not being used consistently across all engineering groups;

(b) applicable service literature requirements had not been inserted into the system of maintenance;

(c) there was possible reliance on verbal communication in the service literature decision process;

(d) there was limited review of the service literature assessment by supervisors;

(e) there was a lack of discipline in checking that action data includes all necessary requirements;

(f) there was a breakdown of communication between and within PPE and MD sections;

(g) the review of the acquitted Action Advices appeared to be on an ad hoc basis; and

(h) there was no documented receipt, assessment and maintenance system revision procedure for introducing MPD amendments;

The review recommended that:

(a) members of engineering groups receive training in service literature handling.

(b) in regard to Action Advices:

(1) Ensure that the addressing reflects the current organisational structure.

(2) Ensure actions required to be taken by the addressee are detailed.

(3) Any response must be in a form that provides an audit trail.

(c) The decision process must not use verbal communication that may by-pass the computer-based recording procedure.

(d) A system of cross checking be introduced to ensure that service literature has been correctly interpreted and subsequent action is accurately presented.

(e) A formal procedure should be introduced to control receipt, assessment and revision certification for MPD amendments.

(f) Introduce a standalone listing of outstanding maintenance related Action Advices.

(g) Carry out a follow-up audit to establish that the recommendations are effective.

2. ANALYSIS

The system employed to receive, assess and incorporate service literature that requires an amendment to the MIM was basically sound. However, the system relied on each person correctly accomplishing a task, but did not specifically require the approving authority to check that the assessment was correct.

The operator’s review of handling of service literature found areas of non-conformance other than those which led to the development of the incident.

3. CONCLUSIONS

3.1 Findings

3.1.1 The manufacturer's requirement for an SFPI inspection of the duct was not included in the operator’s maintenance system.

3.1.2 Personnel who were required to action the documentation received from manufacturers did not follow established procedures.

3.1.3 There were inadequate safeguards in the system of maintenance to detect that established procedures had not been followed.

3.2 Significant factors

3.2.1 Visual inspections of the high-pressure duct did not disclose any evidence of cracking.

3.2.2 An SFPI inspection was not carried out because it was not called up on the relevant check sheet.

3.2.3 The check sheet had not been amended to include an SFPI inspection because of errors in transcribing the manufacturers requirement.

3.2.4 The errors in transcribing were not detected.

3.2.5 The high-pressure duct cracked and ejected hot air into the cowl area which activated the fire warning system.

4. SAFETY ACTION

4.1 The operator has instituted revised procedures that require the approving authority to check that the assessment details are correct.

4.2 The operator carried out a total review of the MPD to ensure that mandatory requirements were correctly assessed and that amendments to the MIM were correct.

4.3 The operator introduced a formal certification system that assures an audit trail of all service literature actions.

4.4 After the amendments to the system had been implemented the operator carried out an audit to ensure that the revised procedures were effective and were being complied with. This audit identified the need for a formal procedure covering the handling of Action Advices. This procedure is to be prepared and introduced on a priority basis.

The crew were carrying out a goat eradication program at the time of the accident. The aircraft was transiting from the hover to forward flight, at approximately 50 feet above ground level, when the engine suddenly stopped.

The pilot immediately entered autorotation and attempted to cushion the landing by increasing the collective pitch. The aircraft touched down heavily, tail first, before colliding with trees.

An inspection of the aircraft failed to disclose any reason for the sudden engine stoppage.

Weather conditions were conducive to the formation of carburettor ice however, the pilot had carburettor heat selected at the time of the accident.

The reason for the sudden stoppage could not be determined.

FACTUAL INFORMATION

Approaching FL190 on descent, Sydney Control requested VH-EAJ to maintain maximum speed and track direct from its position north of Mt McQuoid to the West Pymble locator.

Further descent clearances were issued and approaching 7,000 ft about 35 NM from Sydney the aircraft was transferred to the Sydney Approach controller who then cleared the aircraft to descend to 3,000 ft. The lower limit of controlled airspace on the cleared route between 35 and 22 NM Sydney is 4,000 ft. Two minutes later the controller asked EAJ to report present altitude. After being told that the aircraft was approaching 3,000 ft the controller advised the crew that they had descended below controlled airspace and that there were unidentified radar returns in the vicinity of their aircraft. The altitudes of the unidentified aircraft were not known. The crew initiated a climb and subsequently re-entered controlled airspace 22 NM from Sydney. A review of recorded radar data revealed that during the excursion of EAJ into un-controlled airspace there was no confliction with other traffic.

During the descent the co-pilot was handling the aircraft and the pilot in command was monitoring the altitude of the aircraft in relation to published lowest safe altitudes to ensure that the aircraft remained clear of terrain. Neither pilot was monitoring the position of the aircraft in relation to the control area step lower limit. They believed that air traffic clearances not only provided separation from other aircraft but also ensured that the aircraft remained within controlled airspace.

The Approach controller in issuing a clearance for EAJ to descend from 7,000 to 3,000 ft, did not consider the relationship of the descent path to the control area step lower limit as he considered this to be a pilot responsibility.

The Aeronautical Information Publication, Operations CLT-2, para 14.9 indicated that it is a pilot responsibility to ensure that the aircraft remains in controlled airspace during descent. Although ATC clearances are aimed at keeping aircraft within controlled airspace there is no specific requirement for a controller to do so.

CONCLUSION

Significant Factors

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

1. The flight crew did not monitor the position of the aircraft in relation to the lower limit of the controlled area.
2. The airways clearance did not ensure that the aircraft remained in controlled airspace.
3. The flight crew had an expectation that the airways clearance would ensure the aircraft remained in controlled airspace.
4. The controller was not required to issue a clearance which ensured the aircraft remained in controlled airspace.
5. Instructions regarding the issue of airways clearances contained in the Manual of Air Traffic Services are deficient in that the clearance was not required to ensure that in complying with the clearance, aircraft remain within controlled airspace.

SAFETY ACTION

As a result of this investigation and a similar occurrence (9401495) the Bureau issued interim recommendation IR940164 to the Civil Aviation Authority on 6 July 1994. It stated:

The Bureau of Air Safety Investigation recommends that the Civil Aviation Authority develop procedures that will ensure that where an aircraft has planned flight in CTA, ATC shall issue instructions that maintain that aircraft in CTA, unless the pilot specifically requests alternative processing.

The CAA response received on 9 September 1994 stated:

I refer to Air Safety Interim Recommendation IR940164 regarding aircraft in controlled airspace.

Following ATS advice of the two incidents on 4 June 1994 when a Qantas aircraft descended OCTA en route to Sydney, ATS and DASR specialists agreed that new procedures, which require ATC to issue clearances providing CTA protection for flights planning to remain in controlled airspace, would be introduced.

On 17 June, Regional ATS AIC, Descent Clearances and Control Area Protection, implemented the following amended procedures:

MATS 8-3-2 Level Assignment in Approach Sequence. Except where the provision of "Visual Approach

Procedures" or "Instrument Approaches" apply, unless otherwise requested by the pilot, level assignment an arriving aircraft shall provide the appropriate vertical buffer with the base of the control area.

MATS 9-1-2 Level Assignment in an Arrival Sequence. Unless otherwise requested by the pilot, level assignment for an arriving aircraft shall provide the appropriate vertical buffer with the base of control area.

These amendments were incorporated into MATS via Amendment List No 10, dated 18 August 1994.

The AIP references will remain unaltered as, although there are new ATC procedures, it is the ultimate responsibility of the pilot in command to ensure that the aircraft is operated in accordance with safety requirements. A general issue AIC will be issued shortly to advise all pilots of the amendments and reiterate their responsibilities.

The bureau has classified this response as CLOSED/ACCEPTED

The pilot of VH-TJL reported ready at the holding point for runway 23 and was cleared for take-off. He had noticed the landing lights of Singapore Airlines SIA227 on a 7-mile final and queried the clearance. The air traffic controller confirmed that he was cleared for an immediate take-off.

As VH-TJL commenced to roll, SIA227, which was now on a 2.5 mile final at approximately 600 feet, was cleared to land, but the pilot elected to make a missed approach and commenced a go-around. In the air traffic controller's opinion, an unsafe situation could develop if VH-TJL climbed up towards the overflying Boeing 747, so cancelled its take-off clearance. The take-off was rejected from below V1 speed, and after completing checklist procedures the aircraft taxied from the runway. Garuda Airlines GIA227 on a 3-mile final was cleared to land but also went around.

Pre-dawn conditions existed at the airport with light and variable winds on the ground, but aircraft reported strong south-easterly winds with moderate to severe turbulence above 500 feet which may have allowed a faster than normal final approach. A CAA investigation with supporting information, found that a breakdown in separation standards had not occurred, and runway separation standards would have been maintained if either aircraft had continued its approach for landing.

CIRCUMSTANCES

The aircraft was cruising at FL370, with the pilot in command as the handling pilot. At 150 DME Sydney, the crew were informed of a runway change and to expect a landing on runway 07. The aircraft commenced descent to Sydney at 137 DME, with an initial clearance to FL210. Several minutes after the aircraft left FL370, Sydney Control requested that its speed be increased to maximum to facilitate traffic sequencing.

Further descent clearances were issued to the aircraft until, approaching 7,000 ft at about 35 DME Sydney, it was transferred to Sydney Approach and cleared for further descent to 3,000 ft. The lower limit of controlled airspace on the cleared route between 35 DME Sydney and 22 DME Sydney is 4,000 ft. The aircraft continued to descend at maximum descent speed, leaving controlled airspace at 28 DME. As a result, the aircraft infringed a flying-training danger area before re-entering controlled airspace at 22 DME. A review of recorded radar data indicated that it did not conflict with any other aircraft whilst outside controlled airspace.

During the descent, the crew did not monitor the position of the aircraft in relation to the lower limit of controlled airspace. However, the pilot in command had been monitoring the altitude of the aircraft in relation to published lowest safe altitudes to ensure the aircraft remained safely above terrain. The flight crew believed air traffic clearances not only provided separation from other aircraft, but also ensured the aircraft remained within controlled airspace.

The approach controller, in issuing a clearance for the aircraft to descend from 7,000 to 3,000 ft, did not consider the relationship of the descent path to the lower limit of controlled airspace, as he considered that to be a pilot responsibility. Moreover, he did not notice that it had descended below controlled airspace until the aircraft had levelled at 3,000 ft at about 24 NM from Sydney. As there were no radar returns in the vicinity of the aircraft, and as the aircraft had only 2 NM to run before re-entry, the controller did not warn the crew of their position.

At the time of the occurrence, Aeronautical Information Publication Operations CLT-2, para. 14.9 stated that it was a pilot responsibility to ensure the aircraft remained in controlled airspace during descent. Although ATC clearances were aimed at keeping an aircraft in controlled airspace during descent, there was no definite requirement that they do so.

Significant Factors

1. Instructions regarding the issue of airways clearances contained in the Manual of Air Traffic Services were deficient in that they did not specify that a descent clearance should ensure that aircraft would remain within controlled airspace.
2. The flight crew had the false expectation that the airways clearance would ensure the aircraft remained in controlled airspace.
3. The flight crew did not monitor the position of the aircraft in relation to the lower limit of controlled airspace.

SAFETY ACTION

As a result of this investigation the Bureau issued Interim Recommendation IR940164 to the Civil Aviation Authority. It stated:

The Bureau of Air Safety Investigation recommends that the Civil Aviation Authority develop procedures that will ensure that where an aircraft has planned flight in CTA, ATC shall issue instructions that maintain that aircraft in CTA, unless the pilot specifically requests alternative processing.

The CAA response was received on 9 September 1994. It stated:

"I refer to Air Safety Interim Recommendation IR940164 regarding aircraft in controlled airspace.

Following ATS advice of the two incidents on 4 June 1994 when [...] aircraft descended OCTA en route to Sydney, ATS and DASR specialists agreed that new procedures, which require ATC to issue clearances providing CTA protection for flights planning to remain in controlled airspace, would be introduced.

On 17 June, Regional ATS AIC, Descent Clearances and Control Area Protection, implemented the following amended procedures:

MATS 8-3-2 Level Assignment in Approach Sequence.

Except where the provision of Visual Approach Procedures or Instrument Approaches apply, unless otherwise requested by the pilot, level assignment an arriving aircraft shall provide the appropriate vertical buffer with the base of the control area.

MATS 9-1-2 Level Assignment in an Arrival Sequence.

Unless otherwise requested by the pilot, level assignment for an arriving aircraft shall provide the appropriate vertical buffer with the base of control area.

These amendments were incorporated into MATS via Amendment List No 10, dated 18 August 1994.

The AIP references will remain unaltered as, although there are new ATC procedures, it is the ultimate responsibility of the pilot in command to ensure that the aircraft is operated in accordance with safety requirements. A general issue AIC will be issued shortly to advise all pilots of the amendments and reiterate their responsibilities." The Bureau has accepted this response.

An RAAF C130 Hercules transport aircraft was conducting touch and go circuits using runway 05. The pilot of VH-LOB called for taxy clearance for runway 05 at 1500.22, (time in hours minutes and seconds.) After establishing the distance remaining for an intersection departure as 1190 metres the pilot requested and received approval for an intersection departure.

At 1502.20 the pilot was cleared to line up on runway 05. A clearance for take-off was given at 1502.59 and the pilot quickly applied take off power and commenced the ground roll. The lightly loaded aircraft was soon airborne. The landing gear and then the flaps were retracted. Suddenly the aircraft rolled very rapidly to the left and pitched nose down. Despite application of full opposite aileron and rudder and nose up elevator the pilot was unable to prevent the aircraft from descending left wing down into the ground to the left of the runway.

The investigation concluded that the accident was due to an encounter with wake turbulence from the C130. Under the Manual of Air Traffic Services (MATS) instructions the minimum separation between a light aircraft making an intersection take off behind a medium aircraft, was three minutes. This standard was required to be applied by the air traffic controller at Wagga.

Information provided by the RAAF indicated the C130 was making consistent circuits, with the base call given just after the base leg turn was commenced. They indicated the time from making the call until the aircraft touched down, was 80-90 seconds. After a short ground roll power was re-applied for take-off and lift off was achieved an estimated 150-180 metres beyond the taxiway intersection from which the take off in VH-LOB was commenced.

The time between base calls on the last four approaches for the C130 averaged four minutes and 28 seconds, with all being within eight seconds of this average. The last base call by the C130 crew was at 1459.42, some three minutes and 17 seconds before VH-LOB was cleared for take-off. Considering the C130 crew's estimate of 80 to 90 seconds to touchdown from this call, the indications were that the three minute separation standard was not met.

The controller said that the C130 base leg calls were given when the aircraft was halfway around base leg. He also estimated the time from these calls to touchdown was 30 seconds and to lift off was one minute. On the touch-and-go landing immediately before the accident, the controller believed that the C130 touched down 12 to 15 seconds past the hour, at about the time VH-LOB taxied. Under MATS provisions the controller is allowed to anticipate that the standard will exist at the time of lift off. In the controller's opinion he had the required three minutes separation. He did not, and was not required to, record any times so these estimates could not be verified.

The Civil Aviation Authority (CAA) published an Aeronautical Information Circular (AIC) H 11/1991, on wake turbulence hazards and characteristics. This AIC was still current at the time of the accident. It stated that wake turbulence vortices (there is one from each wing) start at rotation for lift off and end at touch down. These vortices tend to sink until close to the ground and then move sideways at about five knots.

The vortice from the right wing moves to the right, while that from the left wing moves to the left. The light wind conditions existing at the time of the accident, probably resulted in the right-wing vortice remaining above the runway. The AIC stated that in stable conditions wake vortices can exist for in excess of three minutes.

From the available evidence it has not been possible to conclusively establish whether the required separation of three minutes existed at the time VH-LOB took off.

Significant Factors

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

1. The light wind conditions that existed at the time probably resulted in the right wing vortice remaining over the runway.

2. Wing tip vortices generated by normal operations in the C130, persisted long enough and were of sufficient intensity to cause a control loss in VH-LOB.

During a demonstration engine failure after take-off on runway 17, the instructor closed the throttle when the aircraft was approximately 150-200 feet above the runway. He then lowered the nose and selected full flap with the airspeed in the range of 55-60 knots. The aircraft developed a higher than anticipated sink rate which could not be arrested before heavy contact with the runway. During the resulting high bounce, the instructor applied full power in an attempt to go-around. As the propeller had been damaged during the heavy landing, the climb performance of the aircraft was substantially reduced. A further two bounces ensued, during which the nose and left main landing gears collapsed.

More than usual forward trim was required during and after take-off. The autopilot trim actuator ran out of forward trim and then ran continuously to full aft. The crew were unable to adequately manually trim forward. The aircraft returned for a normal descent and landing.

The autopilot Mach trim actuator was found to be inoperative. The actuator had been fitted during overnight maintenance and the observed problem occurred on the first flight after installation. Ground test procedures after installation had not shown up any problems.

Workshop rectification found anomalies with the backlash on the jackscrew and with the actuator length. The manufacturer advised that these anomalies would not have caused the problem that was experienced.

The actuator was refitted four days after the workshop check and has since operated satisfactorily. The cause of the inflight problem was not discovered.

While VH-CZE was lining up a helicopter was cleared for take-off from the southern end of the parking areas to the west of the runway. The helicopter was instructed to remain west of the flight strip and to cruise not above 500 ft.

The helicopter pilot maintained the runway heading for about one mile past the end of the runway before slowly moving left to track around the coast to his destination adjacent to the Cairns city area. When he started to move left VH-CZE was in the latter stages of the take-off. As the crew had expected the helicopter to remain west of the centreline and it had now drifted into their path, they abandoned the take-off. The helicopter was maintaining 400 ft at that time.

The tower controller intended that the helicopter should remain west of the runway until he instructed otherwise. The helicopter pilot was new to the area and did not fully understand the intent of the instruction.

The two aircraft departed Bundaberg on flights scheduled for the same time. Both intended tracking direct to Brisbane at 9000 ft. The same flight pattern had been operated for some months. As a general rule VH-FCU departed first because of the start procedures required by VH-XFO. Because VH-XFO was faster in flight it was normal for that aircraft to overtake VH-FCU during the latter stages of the climb. Both aircraft would continue at their planned altitude with the crews knowing that the faster aircraft was in front and that the distance between the two aircraft was increasing.

On this occasion VH-XFO was overtaking VH-FCU and when about two miles behind that aircraft was turned onto a southerly heading. When the crew were satisfied that they had passed VH-FCU they turned to intercept their direct track (151 degrees). The climb was continued, and some turns were made to remain in visual flight around cloud build-ups. After reaching 9000 ft and cruise speed the crew of VH-XFO advised that their ground speed was 215 kts. The speed of VH-FCU was 200 kts in the cruise.

Some time later, after VH-FCU came out of cloud, VH-XFO was seen at the same level and about 50m to the right. The crew of VH-FCU immediately turned left and descended. The crew of VH-XFO saw the other aircraft and commenced a climb to 10000 ft. VH-FCU was subsequently returned to 9000 ft.

Examination of recorded radar data confirmed the pilots' reports. The two aircraft were less than one mile apart before VH-XFO turned right to increase their spacing. When the aircraft reached their cruising altitude, they were about 4 NM apart and VH-XFO was starting to move ahead of VH-FCU. When the crew of VH-XFO commenced their return to the planned track they conducted an intercept of about 30 degrees. This was later increased to 45 degrees when some manoeuvring around cloud was made. During this period the ground speed also reduced by up to 20 kts. As a result, when VH-XFO was turning, having intercepted the desired track, the two aircraft were in very close proximity to each other.

SIGNIFICANT FACTORS

1. Both flights scheduled to depart at the same time.

2. Both flights elected to utilise the same cruising altitude.

3. The crew of VH-XFO did not realise the implications of:

• diverting off track;
• manoeuvring around weather; and
• making a large-angle intercept of track.

4. The crews did not maintain adequate surveillance on their relative positions.