The disparity between the TAAATS training and management of sector 6, the differences in coordination and management between TAAATS and sector 6 and the limited opportunities to use radar vectoring, all contributed to limit the controller's ability to successfully resolve the conflict.

The ready provision of direct tracking to Mudgee for aircraft that had planned via H29 increased the controller workload. While this factor was minor in comparison to the others previously mentioned, it nevertheless resulted in some additional action by the controller. Had aircraft been required to intercept and rejoin air route H29 prior to the majority of the intersections with other routes it is likely that the complexity of the controller's task would have been reduced.

Prior to the crew requesting the availability of alternative separation methods the controller had formulated a traffic management plan that would ensure separation was maintained between the aircraft. After the crew's query, the controller adjusted his plan to compensate for the changed circumstances but was inadequately prepared to ensure maintenance of separation using the radar.

VH-CZU a Boeing 737 (B737), was en route from Adelaide to Sydney at flight level (FL) 370 on air route H31. VH-CZS a B737 was tracking north on H29 en route from Melbourne to Brisbane at FL370. Their respective air routes intersected at a position approximately 25 NM north-east of Wagga and their relative positions and groundspeeds indicated that the radar separation standard of 5 NM would not be maintained.

The Melbourne Sector 6 controller coordinated with the Canty Sector controller for the crew of CZU to be issued with a requirement to descend to FL350 by 110 NM from Culin, a position approximately 34 NM north of Canberra. The intent of the instruction was to ensure that the vertical separation standard of 2,000 ft was established between the aircraft prior to the lateral distance between them reducing to less than the standard. Following the acknowledgment and read back of the requirement, the crew of CZU queried whether radar vectors would be available, as they preferred to maintain FL370 due to cloud and possible turbulence below that level. The Canty controller advised the crew to stand by and after conferring with the sector 6 controller instructed them to transfer to the sector 6 frequency. Once established on the sector 6 radio frequency the crew was instructed by the controller to turn right heading 130 degrees. The controller issued further instructions to the crew of CZU to turn onto 140 degrees and 150 degrees.

The controller then instructed the crew of CZS to turn right onto 060.

CZU passed 4 miles behind CZS while they were at the same level. There was an infringement of separation standards. The incident occurred during the period when Melbourne air traffic controllers were transitioning from the old centre that used the Australian Computer Air Traffic Control System radar and procedural flight strip bay facilities to new facilities using the Advanced Australian Air Traffic Control System (TAAATS). Sector 6 was in the old centre while Canty sector was a TAAATS position. TAAATS has a number of alarms to alert controllers of potential separation infringements. During the occurrence the short-term conflict alert operated at the Canty position. The sector 6 controller was busy at the time with a moderate level of traffic. The complexity of the management of sector 6 was compounded by weather that was causing flight crews to request advice of weather on various routes and also for diversions to avoid developing weather cells. Sector 6 had two control positions, radar and procedural and was normally operated in the combined configuration. The controller was managing both positions at the time. Another controller was available to assist at the position. This controller was not utilised until after the occurrence.

When CZS entered sector 6 airspace it was approximately 7 NM west of air route H29. This was normal practice as departure controllers were approved to instruct crews to track from their present position, within the terminal area (within 45 NM of Melbourne), direct to Mudgee. This required the sector 6 controller to calculate a specific solution for each potential crossing conflict with aircraft nominally tracking on H29 and aircraft on all intersecting routes. Sector controllers can use lateral separation diagrams to assist in the application of separation. However, the use of such diagrams was dependent upon aircraft operating within the navigational tracking tolerance of the air route being flown. Sector 6 did not have or use lateral separation diagrams.

Sector 6 was a joint radar/procedural sector with a majority of radar coverage. However, the size of the sector and the disposition of air routes within the sector meant that generally conflicts were resolved using procedural control methods. Radar vectoring was used to sequence aircraft for arrival into Sydney but was not generally used to establish separation between aircraft. Consequently, controllers had limited opportunities to practice vectoring techniques.

The controller had returned to the sector 6 staff roster approximately two weeks prior to the occurrence after being rostered for familiarisation training on 30 September and 1 October 1999. The controller had agreed to return to sector 6, following his TAAATS transition training, to enable other controllers to be released for transition training. The sector 6 area of responsibility within TAAATS had been divided into two sectors, Parkes and Bourke. The management of traffic and coordination requirements for these sectors differed considerably from those required for sector 6. The controller had undergone radar vectoring exercises during the transition training but these had focused primarily on developing human-machine interface skills and not traffic management skills. Also, some exercises used nil-wind conditions and thus were not reflective of conditions likely to be experienced on the job. The controller was rostered for two familiarisation shifts on the return to sector 6. However, after five hours during the first period of familiarisation, the controller felt comfortable and believed he was capable of operating at a satisfactory level and was subsequently endorsed to operate the sector.

The crew reported that they believed that the requirement, to descend to FL350 by 110 NM Culin, had been cancelled when the Canty controller advised them to stand by. The sector 6 controller did not instruct the crew to maintain FL370 once he had decided to vector the aircraft. Neither the crew of CZS nor the controller queried or clarified the status of the level requirement until after the occurrence.

Entries in the pilot's logbook indicated that in the past, the pilot had been prepared to abandon flights due to poor weather. This provided some support for the contention by those who knew the pilot that he was cautious with respect to weather. The weather forecasts obtained by the pilot did not indicate that conditions were unsuitable for the flight, and the decision to proceed at that stage was probably appropriate. However, the pilot had reported that the weather conditions while overhead Goondiwindi, approximately one hour before the accident, were not good. It should have become apparent to him as he continued towards the coast that the weather conditions were deteriorating to the point where they were unsuitable to continue the flight.

The investigation was not able to determine why the pilot made a decision to continue with the flight when confronted with weather conditions that were obviously worse than those forecast, and that appeared to be unsuitable for VFR flight.

The pilot's initial handling of the aircraft when in IMC appeared reasonable under the circumstances. The left turn to intercept the track from Toowoomba to Caloundra was performed with a degree of accuracy and was indicative that the pilot was probably using the GPS for navigation. The steady heading and slow but constant rate of descent which were evident after the aircraft was established on track to Caloundra suggested that the aircraft was probably being flown on autopilot.

The subsequent failure of the pilot to fly the assigned heading, the increased ground speed and rate of descent, and the consequent loss of control are consistent with the pilot becoming spatially disoriented during the right turn onto 130 degrees and having disconnected the autopilot. The aircraft impacted the ground in close proximity to the last radar-observed position, less than 90 seconds after the pilot's last radio transmission was received by ATS. Based on witness reports and evidence at the accident site, the aircraft was in a left spiral dive before impacting the ground.

The pilot of a VFR aircraft is solely responsible for ensuring that the flight is operated with due regard for changing weather conditions. In this particular instance, for reasons that were not established, the pilot placed himself in a situation where weather conditions were unsuitable for VFR flight; a situation for which he was not trained or qualified. Having placed himself in that situation, the ATS response became a matter of primary importance. ATS staff play a vital role in assisting pilots in an in-flight emergency situation. The timeliness and effectiveness of that assistance is particularly important when dealing with VFR pilots as they are subject to unique emergency situations and often have limited skills and experience. In addition, as VFR pilots generally operate as a single crew, they rely heavily on external assistance when faced with emergency situations such as inadvertent flight into IMC.

The ATS response to this in-flight emergency would have been enhanced through a greater understanding and application of the strategies and techniques suggested in the Manual of Air Traffic Services, the IFER training manual and the IFER checklist. Controller actions suggested that they did not have the background knowledge to effectively manage the in-flight emergency situation. In particular, the controllers did not appear to be aware of the potential consequences and therefore the priority that needed to be afforded to the pilot.

The strategy adopted by the controller in responding to the in-flight emergency situation was not consistent with the guidance provided in chapter 17 of the Manual of Air Traffic Services, the IFER training manual or the IFER checklist in use. In particular, the pilot was placed in a situation where he was turning and descending the aircraft at the same time. In addition, the pilot was also required to respond to questions from ATS while performing these manoeuvres. It was unlikely that the pilot had the skills or experience that were required to enable him to cope with these demands. Although the controller's communication style was in accordance with standard phraseology, the authoritative and interrogative style was inappropriate in the circumstances and was unlikely to have instilled confidence in or reassured the pilot.

Although the Manual of Air Traffic Services provided basic guidance on the strategy needed to deal with a VFR pilot operating in IMC and although the IFER checklist served as an aide-memoire, neither provided the level of detail contained in the IFER training manual. It is significant that this, or an ADF equivalent, manual was not available to ADF ATS units.

The circumstances of this accident are consistent with an uncontrolled collision with terrain following the pilot's loss of adequate external visual reference. It is likely that he became spatially disoriented and lost control of the aircraft soon after descending through 3,200 ft. The aircraft subsequently entered a left spiral dive before impacting the ground. As a result of concerns regarding military air traffic control officers' awareness of in-flight emergency response practices and procedures for civil aircraft, the Australian Transport Safety Bureau issued interim recommendation IR19990190 to the ADF on 16 December 1999.

The pilot of a Cessna 182J was conducting a private visual flight rules (VFR) flight, with one passenger, from Lightning Ridge to Caloundra. The passenger was also a qualified private pilot.

Prior to departure at about 0845 EST, the pilot obtained an Airservices Australia location briefing containing weather and notice to airmen (NOTAM) information relevant to the flight. At about 1000, the pilot used a mobile phone to contact an associate in Lightning Ridge. The pilot indicated that he was over Goondiwindi, tracking via Toowoomba for Caloundra, and that the weather was not good.

At approximately 1100, the Australian Defence Force (ADF) Amberley approach controller observed an unidentified code 1200 secondary surveillance radar (SSR) return in close proximity to the boundary of military airspace, about 10-12 NM north-east of Toowoomba. Code 1200 is allocated to VFR flights operating outside controlled airspace and not participating in a radar information service. The SSR return provided unverified mode "C" altitude information that indicated the aircraft was at 5,700 ft above mean sea level. The controller soon became concerned that the aircraft was going to enter controlled airspace, and that it might conflict with a General Dynamics F111 that was inbound to Amberley from the north with an in-flight emergency.

The controller attempted to contact the pilot of the unidentified aircraft by making a number of general broadcasts on the Amberley approach frequency. The controller also requested that the Airservices Australia Downs radar advisory service controller make a general broadcast for the pilot to contact Amberley approach, which he did at 1106:37. The Amberley approach controller informed the pilot at 1107:57 that his aircraft was identified on radar. At that time the aircraft was inside Amberley controlled airspace bearing 310 degrees M and 30 NM from Amberley. The pilot was immediately instructed to conduct a left orbit to provide separation with the F111.

During the orbit, the pilot advised the controller that the aircraft was "caught in cloud" and that he was "in trouble". A number of broadcasts between the controller and the pilot subsequently took place as the controller attempted to clarify the situation. During that time, the pilot asked whether he could use the automatic pilot. The quality of the radio transmissions from the aircraft was poor and the controller had difficulty in comprehending the full extent of the problem and the pilot's request to use the autopilot. The controller reported that these difficulties were exacerbated by the pilot's accent.

By the time the controller established that the pilot wanted to track to Caloundra and was rated only for VFR flight, but was in instrument meteorological conditions (IMC), the pilot had commenced a second left orbit. The aircraft was approximately half-way through the second orbit, passing a heading of approximately 240 degrees when the controller instructed the pilot to turn right and take up a northerly heading for Caloundra. While the aircraft was in the right turn, the controller asked the pilot if he wanted descent, to which the pilot replied in the affirmative. The controller then cleared the pilot to leave control area on descent.

Changes in the aircraft's altitude during the right turn were erratic. Radar recordings indicate that the aircraft descended to 4,400 ft in less than a minute, then climbed back to 4,800 ft. The pilot maintained the right turn onto a heading of about 130 degrees before making a left turn to intercept the track from Toowoomba to Caloundra. During that time, the controller advised the pilot that he could descend to 3,000 ft safely in the aircraft's current location. Once established on track to Caloundra, the aircraft maintained a steady heading, with a rate of descent of about 300 ft/min.

After the aircraft was established on track for Caloundra and was still in IMC, the controller became concerned that the aircraft was heading for an area of higher terrain, where the radar lowest safe altitude, as specified on the radar terrain clearance chart, was 3,800 ft. As a result, the controller instructed the pilot to turn right heading 130 degrees (a turn of about 90 degrees). The aircraft was passing 3,700 ft when the pilot commenced the right turn. Recorded radar data indicated that the aircraft continued the right turn through the assigned heading and that the aircraft ground speed and rate of descent increased during the turn.

The aircraft SSR return disappeared from the radar display at approximately 1116 as the aircraft was passing 3,200 ft on a heading of about 210 degrees. Controllers at Amberley reported that that was consistent with known radar coverage in the area. The pilot responded to a question from the controller regarding the aircraft's in-flight conditions at approximately 1116:00. Radio contact with the pilot was lost after that time. The Amberley approach supervisor subsequently contacted the emergency services number to find out if there had been any reports of accidents. The supervisor was switched through to Ipswich police, who advised that they had received a report of an accident in the Esk area.

The wreckage of the aircraft was located approximately 6.5 km north of Esk on flat pastoral land. A nearby resident caught a glimpse of the aircraft just before impact and then observed a plume of fuel and debris. He immediately notified emergency services, who recorded the call at 1117:30. Impact evidence indicated that the aircraft was in a left turn in a nose-low attitude and that the aircraft was not in a stalled condition. This is consistent with witness reports that indicate the aircraft was descending in a left turn. The impact destroyed the aircraft and both occupants were fatally injured.

Pilot in command

The pilot held a private licence, together with a valid class two medical certificate, and was appropriately endorsed. However, he did not hold a rating for flight in IMC, nor was the aircraft approved for flight in IMC. The pilot had logged a total flight time of 220 hours, comprising 90 hours dual and 130 hours as pilot in command by day. No evidence was found that the pilot was suffering from any medical condition that could have contributed to the accident.

The pilot was reported as being cautious and conscientious in his approach to flight preparation and in-flight procedures. In particular, flying instructors who had flown with the pilot reported that he was wary of flying in poor weather. The pilot's logbook indicated that on at least three previous unrelated occasions, the pilot had abandoned flights and returned to Lightning Ridge due to adverse weather. An associate of the pilot reported that he spoke to him prior to his departure on the day of the accident and that the pilot had expressed reservations about making the flight to Caloundra. He had stated that he intended assessing the weather at Goondiwindi before proceeding further.

Aircraft information

A periodic maintenance inspection was due approximately 10 hours after the commencement of the accident flight and there were no known outstanding maintenance defects. Evidence indicated that the engine was operating at impact and examination of the wreckage did not reveal any deficiencies that were likely to have contributed to the accident. The aircraft was fitted with an emergency locator transmitter (ELT), which was destroyed on impact. A global positioning system (GPS) unit was fitted to the aircraft and the pilot was also carrying a hand-held unit.

Meteorological information

On the morning of the flight, the pilot obtained area forecasts (ARFORs) 22, 40 and 41, which covered his route. He also received terminal area forecasts (TAFs) for relevant en-route airfields and for Maroochydore and Archerfield, but there was no evidence that he received a TAF for Caloundra. ARFOR 40 covers a large part of south-east Queensland, including the eastern Darling Downs and the Amberley area.

The Area 40 forecast was valid from 0717 to 2100 EST. The forecast overview indicated cloudy conditions with rain areas and isolated thunderstorms, clearing from the west after 1800. Forecast cloud consisted of isolated cumulo-nimbus with a base of 6,000 ft and scattered stratus between 1,200 ft and 6,000 ft in rain, broken near thunderstorms. Also forecast was scattered cumulus and strato-cumulus with a base of 3,000 ft between the coast and the ranges and 4,500 ft inland, with broken alto-cumulus and alto-stratus layers above 16,000 ft. The predicted visibility was 5,000 m in rain and smoke and 2,000 m in the vicinity of thunderstorms.

The TAFs for Archerfield and Maroochydore were current from 0600 to 1800 EST. They predicted visibility in excess of 10 km, light rain and scattered cloud at 2,500 ft, and also forecast intermittent periods of reduced visibility down to 4,000 m, rain and broken cloud at 1,000 ft.

The pilot of the F111 reported that the area was dominated by large cumulus cloud with associated stratus. He reported that there were occasional gaps between the cumulus and stratus cloud levels, which resulted in small pockets of airspace where visual flight was possible. However, these pockets were only present above 5,000ft and were totally surrounded by cumulus and stratus cloud. The crew of the F111 reported that the cloud during their approach to Amberley, approximately 30 NM to the south-east of the accident site, was consistent broken low cumulus and stratus with a base of 650 ft above mean sea level.

A Bureau of Meteorology observer at Amberley stated that on the day of the accident, the weather was influenced by an easterly moving trough lying north-south through central Queensland and a north-easterly breeze off the ocean. The observer stated that these two influences were known to produce a build-up of low cloud against the ranges. Witnesses on the ground in the vicinity of the accident site described the weather as showery, with cloud covering the tops of the hills.

Air traffic services inflight emergency response

Air traffic services (ATS) emergency procedures were outlined in chapter 17 of the Manual of Air Traffic Services, a joint military/civil document. Section 3 of chapter 17 provided guidance on emergency phase declaration. Paragraph 1 stated that "[t]he appropriate emergency phase shall be declared to show the degree of apprehension felt for the safety of an aircraft and an indication of the scope of the SAR [search and rescue] action to be provided." Paragraph 6 stated that "[a]n Alert Phase exists when there is apprehension as to the safety of an aircraft and its occupants", and specifically noted that an Alert Phase existed when a flight restricted to visual meteorological conditions (VMC) was operating in IMC.

Section 4 of chapter 17 referred specifically to procedures for the handling of in-flight emergencies by ATS staff. Paragraph 1 of section 4 stated:

"While it is impracticable to set out a detailed response to every emergency situation, it is possible to identify broad groups of incident types and to generalise appropriate courses of action".

Paragraph 2 stated:

"In resolving inflight emergencies, units should use the Inflight Emergency Response Checklists as a basis for the provision of assistance to pilots".

Information and guidance specific to "Flight confined to VMC but operating in IMC" was contained in paragraphs 48 to 53 of section 4. Paragraph 48 highlighted the fact that "[t]his type of inflight emergency is potentially a very serious situation which has often led to fatal consequences".

The section also provided general guidance to ATS staff on issues about which they needed to be aware, and strategies to be employed in responding to this type of in-flight emergency. In particular, it stated that ATS staff should be aware that a pilot in this situation would have difficulty with the following:

1. maintaining headings;
2. maintaining altitude; and
3. perceiving aircraft attitude.

Furthermore, the section stated that ATS should endeavour to provide reassurance to the pilot in the initial communications and limit communication so as not to divert the pilot's attention from flying the aircraft.

More detailed guidance on handling in-flight emergency response situations was provided in Airservices Australia's Inflight Emergency Response (IFER) Training Manual. The IFER training manual expands on specific issues listed in the Inflight Emergency Response Checklists.

The ATS strategy for an aircraft in a "VFR in IMC" situation was detailed in the IFER training manual and stated that it "should reflect the absolute pilot priority to control the aircraft ahead of navigation or communications". The following advice to assist pilots in such a situation was provided in the training manual:

"

1. Provide the pilot with some reminders on aircraft handling. While [the controller] is not expected to "fly" the aircraft for the pilot, the following handling actions are universally recognised as appropriate basic advice to an inexperienced pilot in distress:

   1. concentrate on aircraft attitude ie.:

      - maintain steady heading;
      - keep wings level;
      - keep speed constant

   2. trust instrumentation;

   3. when manoeuvring commences:

      - no abrupt manoeuvres;
      - shallow/climbs/descents/turns;
      - turns first, establish straight and level then climb/descend,

2. Provide navigation information to the pilot that will allow the aircraft to be re-established in VMC.
3. Communicate with the pilot using the following techniques:
   1. keep instructions simple and distractions to a minimum;
   2. keep regular radio contact without overloading;
   3. instil confidence and reassure the pilot; and
   4. pass only one item at a time

The IFER training manual also provided guidance on the communications style which should be adopted by controllers when dealing with this type of emergency. Specifically, the manual noted that a VFR pilot in an IMC situation is under considerable stress and there was a need for ATS staff to convey empathy, patience and confidence. This required ATS staff to adopt a markedly different technique to the customary delivery of ATS information, where precision and economy of words are appropriate to communications between confident professionals. Furthermore, in establishing the necessary background information, it was vital that questions not be put in an interrogative manner.

The IFER checklists, a document separate from the IFER training manual, contained items that should be considered when responding to specific situations. However, checklists serve primarily as an aide-memoire. A high level of background knowledge and situational awareness by the controller is required to expeditiously provide assistance to the pilot. In this regard, while the checklists are a useful tool, they need to be considered in conjunction with more detailed guidance, such as that contained in the IFER training manual.

A review of the audio voice recording revealed that the controller's manner while communicating with the pilot was authoritative, with questions being posed in an interrogative style. The controller used the IFER checklist during communications with the pilot. However, the unit was unaware of the existence of the IFER training manual.

The register of copy holders in the front of the IFER training manual indicated that ADF was a registered holder of three copies. However, the ADF was unable to locate these copies and the manual was not held by any ADF ATS unit. Airservices Australia records did not provide any receipt confirmation advice relating to the document copy numbers listed against the ADF.

On 9 October 1999, a Fokker F28-100 aircraft, on a direct service from Brisbane with 84 persons on board, experienced severe vibration through the airframe during landing at Norfolk Island. The crew stopped the aircraft on the runway and, after a preliminary examination, taxied the aircraft to the terminal where the passengers disembarked normally. There were no injuries.

Investigation revealed that the left main landing gear upper torque link attachment lugs had broken. The upper torque link attachment point on the landing gear main fitting was an integrally forged double lug with a stiffening web between the two lugs. The maintenance documentation showed that the main landing gear had completed 16,579 cycles since new and 658 cycles since last overhaul.

The Australian Transport Safety Bureau (ATSB) conducted specialist fracture analysis of all the broken landing gear components. The specialist report concluded that the failure of the torque link attachment lugs was associated with the extension of pre-existing cracking in the lug-stiffening web while torque was transmitting through the torque links. The initial cracking in the web was caused by stress corrosion. The propagation of the fatigue crack was consistent with a loading regime that involved the sideways flexing of the wheel rim. This will occur when a turning moment (torque) is applied to the main landing gear while the wheels are rotating, such as during ground turning or crosswind landings.

The evidence showed that the region of the pivot pin bore and locating pinhole had been reworked during overhaul. At that time material had been removed by localised surface grinding to remove corrosion. The pivot bore surface was then shot peened and repainted with a chromate based paint primer. However, the paint primer exhibited poor adhesion, and the shot peening coverage was haphazard. Consequently, these measures had been ineffective in preventing stress corrosion.

The final failure of the torque link attachment lugs occurred during the initial stage of the landing and occurred while the landing gear was being subjected to significant torque loads. It is likely that the torque loads were associated with crosswind conditions. The crew report for a previous landing incident with this aircraft at Norfolk Island, indicated that crosswind components of 15 knots or higher are regularly experienced during operations at Norfolk Island.

The operator's maintenance facility reported that part of the left main gear shimmy damper was found to have been wrongly re-assembled during last overhaul. The fracture analysis evidence indicates this would have had minimal if any influence on the start or development of the fatigue cracks that led to the failure of the torque link attachment lugs.

A previous incident occurred on 4 July 1999, involving the left main landing gear of this aircraft, also while landing at Norfolk Island. In that incident, ATSB occurrence number 199903327, the outboard main landing gear wheel broke away from the wheel hub during the landing roll. The ATSB specialist fracture analysis report (see below) found the wheel failure had started and progressed in similar circumstances to those for the torque link attachment lugs.

At the time of the occurrence the environmental wind was strong, and the investigation concluded that it was likely that the downdrafts and associated surface outflows from the entrained convective activity were distorted in the direction of the prevailing airstream, and that this accounted for the gusting conditions that were present at the time of the occurrence.

The flight data recorder fitted to EBS was not equipped to record the aircraft's groundspeed, and the investigation was unable to determine the actual external winds that affected it during the approach and landing. However, from the meteorological data that was available, it was probable that the roll rate encountered by EBS as it commenced the landing flare resulted from an encounter with low-level windshear. It is likely that this was produced by a downdraft from one of the convective storm cells passing through the terminal area at the time.

Although the pilot in command responded in a timely manner with appropriate control input, under the dynamic conditions that were encountered, it is unlikely there was sufficient available aileron/spoiler authority to counteract the high rate of roll that had suddenly been experienced. This resulted in the number 1 engine pod momentarily striking the ground as the aircraft touched down.

Low-level windshear may occur as a result of thunderstorms, land/sea breezes, low-level jet streams, mountain waves and frontal systems. There have been accidents and incidents associated with low-level wind shear in Australia. Pilots should be aware that it is a phenomena that may occur at any location, is difficult to predict, and can present a hazard to aircraft on approach and departure.

History of the Flight

On arrival at Perth, the crew of a Boeing 747-238B, VH-EBS, were cleared to conduct an instrument approach for landing on runway 03. The pilot in command was the handling pilot for the sector, and the crew subsequently reported that although they were in visual meteorological conditions during the approach, turbulence was encountered. Information "Whisky" was being broadcast on the automatic terminal information service (ATIS), and provided information to the crew that the wind speed and direction at the aerodrome was 330 degrees magnetic at 20 knots. The ATIS included information that the wind speed and direction at 200 ft above ground level was 330 degrees magnetic at 30 knots, and advised crews to expect moderate turbulence below 4,000 ft.

During the approach the co-pilot requested a wind check from the aerodrome controller. The controller advised the crew that the runway 03 threshold wind was 300 degrees at 12 kts, giving a crosswind of 12 kts. The controller requested the crew to advise the spot wind at 1,000 ft, and the co-pilot reported that the 1,000 ft spot wind was 280 degrees at 35 kts.

On short final, at approximately 500 ft above ground level, the pilot in command discontinued the approach when the aircraft experienced turbulence rendering the approach unstable. The co-pilot notified air traffic control (ATC) that EBS was conducting a missed approach, and the controller issued an instruction to the crew to climb to 1,500 ft. The controller then issued further instructions for EBS to climb to 3,000 ft and instructed the crew to take up an easterly heading to intercept the 9 mile arc, from the Perth distance measuring equipment beacon, to position the aircraft for another approach onto runway 03.

As EBS proceeded towards the south to intercept the 9 mile arc for the second approach to runway 03, the controller reassessed the prevailing wind conditions. The wind had been steadily backing to a more southerly direction, and the controller considered that the wind had begun to favour operations on runway 24. The controller notified the crew of EBS that runway 24 was available for landing, and the crew advised that they would accept an approach for that runway. The controller then issued radar vectors to the crew to position EBS onto the approach for runway 24. As EBS was on final approach the controller advised the crew that the threshold wind for runway 24 was 290 degrees at 23 kts, and that the wind at 200 ft was 290 degrees at 35 kts.

The crew reported that the approach to runway 24 was conducted normally and with the autopilot engaged. However, turbulence had prevailed throughout the approach. Flaps 30 was the landing flap setting, and as the aircraft flared for touchdown it suddenly experienced an unexpected roll to the right and the pilot in command applied a control wheel input to the left to counter the roll. The aircraft then suddenly experienced a severe roll to the left. Although the pilot in command applied an immediate control wheel input to the right to arrest the roll, the aircraft touched down in a left wing down attitude, and the number 1 engine pod briefly struck the runway surface.

The crew reported that the touchdown was smooth, and appeared to be on the centreline of runway 24. They also reported being unaware that the number 1 engine pod had struck the ground during the touchdown. As the aircraft taxied in to the international apron a flight attendant advised the crew that a passenger had reported seeing brown fluid leaking from the number 1 engine. After the aircraft had parked the number 1 engine was inspected for damage. The casing of the high speed external gearbox fitted to the engine was fractured adjacent to the gearbox mount position, and the number 1 engine thrust reverser was damaged. The pilot in command then notified the controller that EBS had sustained a podstrike during the landing on runway 24.

The subsequent inspection of runway 24 revealed a scrape mark on the runway approximately 490 metres from the threshold of runway 24. The scrape mark was approximately 30 metres in length and was located approximately 18 metres left of the runway centreline just outside the outer edge of the runway touchdown zone markings. Examination of the manufacturer's data for the B747-200 series showed engine number 1 to be 21.2 metres outboard from the aircraft centreline. This was consistent with position of the scrape mark on runway 24.

Flight Data

Air traffic control radar plots and the flight path derived from EBS's flight data recorder (FDR) were examined during the investigation. They revealed that the pilot in command discontinued the first approach onto runway 03 at 04:07 co-ordinated universal time when EBS was at approximately 500 ft above ground level. Following the discontinued approach onto runway 03, EBS was vectored to the southeast of the airport, then back towards the northeast when ATC reconfigured the terminal airspace for operations onto runway 24. EBS commenced the approach onto runway 24 at 04:23, and the approach concluded at 04:28 when the aircraft landed.

The FDR roll angle plot revealed that as EBS was 35 ft above ground level it commenced an uncommanded roll to the right. The pilot in command immediately applied 29.5 degrees of left control wheel to counteract the roll. However, the roll continued to increase, and EBS was in an 8.0 degrees right wing down attitude as it reached 2 ft above ground level. The roll then suddenly reversed, and within 2 seconds EBS was in an 8.4 degrees left wing down attitude. Although the pilot in command immediately responded with 40.7 degrees of right control wheel to counteract the roll, the aircraft touched down still in an 8.4 degrees left wing down attitude.

Groundspeed was not a recorded parameter on the Lockheed LAS209F FDR that was fitted to EBS, and the investigation was therefore unable to determine the actual wind conditions that it encountered throughout the approach. However, variations in the FDR computed airspeed plot throughout the occurrence sequence were consistent with the reported turbulent conditions.

Aircraft Data

Roll control of the Boeing 747 aircraft is provided by inboard and outboard ailerons and spoilers. The manufacturer advised that a control wheel deflection of 40.7 degrees to roll the aircraft to the right would result in outboard aileron deflections of left outboard +13.8 degrees and right outboard -22.2 degrees. The maximum outboard aileron deflection is +15 and -25 degrees, with +ve signifying trailing edge down and -ve signifying trailing edge up. With the same control wheel deflection of 40.7 degrees to roll the aircraft to the right, the resultant inboard aileron deflections would be left inboard +18.2 degrees and right inboard -17.9 degrees. Normally the maximum inboard aileron deflection is +/- 20 degrees.

The spoilers consist of 12 panels on both wings starting with no 1 on the left outboard wing and extending to no 12 on the right outboard wing. For a control wheel deflection of 40.7 degrees to roll the aircraft to the right, spoilers 1-7 would be deflected 0 degrees (faired with wing), spoiler 8 would be deflected 9.7 degrees, and spoilers 9-12 would be deflected 15.3 degrees. Aileron and spoiler deflection would be reversed for a control wheel deflection of 40.7 degrees to roll the aircraft to the left.

Data for Boeing 747-200 series aircraft fitted with Rolls Royce RB211-524 engines showed that the ground clearance of the number one engine pod was 188 cm at an operating empty weight of 164,610 kgs. This clearance was reduced to 158 cm when the aircraft was at its maximum taxi weight of 352,894 kgs. The plan view of the Boeing 747-200 series aircraft showed the number 1 engine to be 21.2 metres outboard of the aircraft centreline, and 15.2 metres outboard of the outboard wheel of the wing landing gear assembly. Under static conditions and with 0 degrees nose pitch, a body roll of 7.05 degrees at the operating empty weight would cause the number one engine pod to contact the ground. A body roll of 5.93 degrees at the maximum taxi weight would also result in ground contact of the number one engine pod.

The weight of EBS at the time of the occurrence was approximately 230,000 kgs.

Meteorological Information

At the time of the occurrence, Perth was under the influence of an unstable air flow as a result of a complex low-pressure system situated to the south of Western Australia. A series of fast moving cold fronts were embedded in the strong to gale force westerly airstream, and the unstable atmosphere resulted in widespread rain showers, squalls and occasional thunderstorm activity.

The trend type forecasts (TTF's) for Perth from 00:33 leading up to the time of the occurrence indicated that gusty wind conditions could be expected in the terminal area. Additionally, the TTF's from 01:31 indicated that thunderstorms were also likely to be present in the area. The aerodrome forecast current for Perth at the time of the occurrence also indicated the likely presence of gusty conditions and rain showers. At 01:00 an airport warning was issued for Perth containing information that a series of squall lines were expected to cause wind gusts to 45 knots during the day, and that thunderstorms were predicted. At 01:13 information concerning en route weather phenomenon with the potential to affect the safety of aircraft operations (SIGMET) was issued. The SIGMET, valid from 02:00 until 08:00, forecast the presence of severe turbulence below 4,000 ft for the Perth region, and was passed to the operator by the Bureau of Meteorology.

The Perth aerodrome ATIS was changed to information "Whiskey" at 03:03. It provided information that the wind speed and direction was 330 degrees magnetic at 20 kts, and warned pilots to expect moderate turbulence below 4,000 ft. A windshear alert was also provided, with the wind speed and direction at 200 ft being 330 degrees magnetic at 30 kts. The windshear alert was included on the ATIS because there was a 10 kts difference between the wind speed on the ground and the wind speed at 200 ft. The ATIS was amended to information "X-Ray" at 04:27, providing information that the wind speed and direction were 290 degrees magnetic at 25 kts. The revised ATIS continued to provide a warning of moderate turbulence below 4,000 ft and also a windshear alert.

Wind shear is defined as a sudden change in wind direction and/or speed with height or horizontal distance. In most cases wind shear does not present a hazard to aircraft and the majority of pilots will be familiar with changes in wind direction and speed as they ascend or descend. However, at low altitudes (below 1000 ft) during critical stages of landing and takeoff, wind shear can present a significant hazard to aircraft because there is a limited ability to undertake a recovery manoeuvre if the aircraft configuration changes. Low altitude windshear events are small scale and short lived and only affect the approach / departure flight path for a short period of time. The ability to identify such events based on traditional airport observations is limited, although systems which can detect wind shear and provide alerts in a timely manner are available.

The Bureau of Meteorology

anemometer at Perth airport was the source of wind data transmitted on the ATIS. The anemometer sampled the wind at 1-second intervals, and a display of the anemometer wind data was located in the control tower. Controllers were able to select the display for instantaneous, 2-minute average wind speed and direction, or 10-minute peak wind speed. Data from the Bureau of Meteorology anemometer was recorded and archived. The control tower also had displays of threshold wind data obtained from anemometers located adjacent to the threshold of each runway. A display also provided wind data from an anemometer located on the control tower cabin. The controllers could select the threshold anemometer and tower cab displays to provide instantaneous, 2-minute average wind speed and direction, or 10-minute peak wind speed. The controllers reported that their usual practice was to leave the tower cab displays selected to the instantaneous setting, with selection to the 2-minute average wind speed and direction or the 10-minute peak wind speed settings being made to determine the development of any significant trends. Data from the threshold and tower cab anemometers was not recorded and archived.

Radar imagery taken at 20 minute intervals during the occurrence period showed a significant line of enhanced rain echoes passing through Perth at 03:20 in a generally easterly direction at approximately 35 to 40 kts. Scattered convective showers were present behind the line of precipitation, with rain echoes being randomly spaced and largely unorganised. The radar imagery also revealed showers in the vicinity of Perth aerodrome at the time of the occurrence.

The 1-minute data recorded by the Bureau of Meterorology anemometer at Perth aerodrome showed that a fast moving front passed across Perth aerodrome at 04:12, shortly after the pilot in command discontinued EBS's approach onto runway 03. The front was associated with a change in wind direction and a significant increase in windspeed for a period of approximately 3 minutes. At 04:26 the 1-minute anemometer data revealed a marked increase in wind speed which persisted until approximately 04:30. The wind speeds increased to 23 - 25 kts during this period, with maximum wind speeds being recorded at 27 - 35 kt. At 04:28, the time of the occurrence, the maximum wind speed was approximately 29 kts. However, during the period 04:26 to 04:30 there was little variation in the recorded wind direction, and it remained relatively constant from the west. The duration of the increase in wind speed was considered characteristic of an outflow from a convective rainshower.

1. The right-wing landing light wiring cable tie stand-offs were not installed.
2. The right-wing landing light wiring was in contact with the surface of one or more fuel lines in the right-wing equipment bay.
3. The wiring had electrically arced on the surface of one or both of the fuel lines resulting in holes being made in the fuel line walls with resultant fuel leaks from each line.
4. The fuel had ignited resulting in fire damage to the adjacent aircraft structure.
5. The fuel leaks were unable to be stopped by the flight crew.

The investigation was unable to determine with any certainty at what time during the flight the fire began. Indications are that the fire was probably not an in-flight fire. The damage to the surrounding structure of the wheel well appeared to indicate plastic deformation and some melting of the aluminium structure, and a probable maximum fire temperature of around 700 ^o C. The crew had reported good illumination from the landing lights for landing. This indicated that all lights were still operating, and that at that time the mechanical indicating fuse was intact. The pilot's actions in not selecting the standby boost pump to on, following the R FUEL PRESS LOW indication, may have inadvertently been a mitigating factor in the fire. The pump could have supplied the fire with extra fuel under pressure at a critical time.

Several years prior to the incident the right wing de-ice boots had been removed and the wing repaired as a result of hail damage. This repair entailed some disconnection and disturbance of the pneumatic lines and electrical wiring running through the forward area of the wing bay. It is possible that the missing landing light electrical wiring cable tie stand-off had been removed and not replaced at this time. The fact that the cable tie impressions on the pneumatic line fire sleeving were covered with soot from the fire, also suggests that the tie was not in place. The area immediately surrounding the landing light cable tie stand-off was also less severely heat affected than other areas in the zone where the remains of cable ties still existed. For example, in an adjacent area there was still considerable evidence of the cable tie that secured and positioned the standby pump electrical wiring. Had the landing light cable tie been in place at the time of the incident, some remains of it should still have been evident.

As there was no visible evidence of chafing between the landing light wiring and the fuel lines, it is possible that the electric arcing may have been the result of the plastic deformation and subsequent breakdown of the wire's ETFE insulation. This could have occurred while the wiring was in contact with the fuel lines, following the generation of excessive heat in the landing light wiring due to the excessive 'contact bounce' in the K11 relay.

The fuel ignition source may have initiated from one of several sources. For example: the electrical arcing between the electrical wiring and the fuel tubing, arcing of a fuel drenched electrical aircraft component, the main gear up position indicator switch, and/or possible static electricity generated by the fuel escaping from the damaged fuel lines. The fuel 'washing' marks against the upper panel suggests that the fire was not burning in that area. Further, the area immediately surrounding the motive flow line leak only exhibited evidence of heat damage and sooting.

The suitability of the ampere rating of the enclosed link, current limiting fuse was also discussed with the aircraft's manufacturer, due to the fact that the fuse delay had allowed the wiring to arc through the fuel lines. Following a review of the wiring system and the current limiter's rating, the aircraft's manufacturer decided that it was appropriate for the task.

The fire may have started following the holing of the engine supply line in the rear of the wing zone, and spread from there. There was evidence of a well-established fire in this area, with some of the ethylene-tetrafluoroethylene copolymer (ETFE) wiring insulation completely burnt away. It is also possible that the holed fuel lines allowed the fuel to run down onto the landing light gear up position indicator switch. This switch initiating the fire when it was momentarily powered during the landing gear extension cycle.

It is probable that the electrical arcing and fire occurred either immediately prior to, or just following landing. Had this fire been burning in flight it is likely that a more serious outcome would have resulted. The inability of the flight crew to isolate the fuel leaks, together with the extreme heat of an inflight fire, could have resulted in the wing spar losing structural integrity, and a possible in-flight loss of the right wing.

After landing, and while taxying to the terminal, the co-pilot of the Beechcraft 1900D aircraft turned the landing lights off. He then contacted Air Traffic Control, cancelling SARWATCH. During this radio transmission, the MASTER WARNING and right AC bus (R AC BUS) warning captions illuminated, closely followed by illumination of the right fuel low pressure (R FUEL PRESS LOW) warning.

The crew immediately carried out the company check list actions for the right AC bus failure, but decided not to implement the actions for the right fuel low pressure warning as the aircraft was close to the terminal. The checklist actions for the right low fuel pressure indication required the standby boost pump to be switched on. The co-pilot then detected an acrid smell in the cockpit and alerted the pilot to flames he had observed coming from the underside of the right engine nacelle. The pilot in command immediately brought the aircraft to a stop, shutting down both engines.

Although there was no engine fire warning indication, the crew operated both engine fire handles, making several unsuccessful attempts to discharge the right engine fire bottle. The co-pilot then evacuated the passengers through the forward cabin door, directing them to the flood lit terminal apron area. The pilot in command alerted the RAAF fire personnel by radio of the fire, before turning off the aircraft power and vacating the aircraft.

Two of the operator's maintenance engineers, awaiting the aircraft's arrival, had noticed the flames emanating from the wheel well area as the aircraft approached. They had immediately picked up two dry chemical powder fire extinguishers and approached the aircraft. Following the feathering of the right propeller, they discharged the contents of both fire extinguishers into the right main landing gear wheel well area, extinguishing the fire. The military fire tender arrived soon after to assist.

Investigation

The investigation found that there had been a fuel-fed fire in the area to the rear of the right main landing gear wheel well, and in the right wing equipment bay area positioned immediately outboard of the right engine nacelle. The fire had severely damaged the airframe structure, wiring and components in both areas. The greatest damage was evident in the rear of the wheel well. The aluminium inner fender panel assembly, positioned at the rear of the right wheel well, had partially melted during the fire, leaving a trail of molten aluminium that extended back along the taxiway.

Fuel to the fire had been supplied from two damaged aluminium alloy fuel tank lines in the right wing equipment bay. One line was positioned toward the front of the enclosed equipment bay area, and the other toward the rear. Examination of the surfaces of both fuel lines indicated that they had been in contact with powered electrical wiring. This contact had resulted in electrical arcing, with holes being burnt completely through the walls of both fuel lines. The wiring supplied power to the right, wing mounted, 450 watt landing light.

The damaged fuel line, positioned in the forward area of the bay, was the fuel transfer motive flow line that supplied the operating pressure to the forward fuel transfer jet pump (See Fig 1). The jet pump transferred the fuel from the main wing tanks to the wing mounted collector tank, ensuring a constant fuel supply for the engine driven pump. This line was pressurised with fuel from the engine driven fuel pump, or by the electric standby boost pump when that pump was turned on.

The damaged fuel line in the rear of the bay was part of the main fuel supply from the wing mounted collector tank to the engine driven pump. The line was positioned between the fuel filter shut-off valve, just forward of the wing main spar and the fuel filter assembly.

The standby electric pump, located in the bottom of the collector tank, served as a backup to the engine driven pump in the event of a failure of that pump, and could be manually selected on by the flight crew. The pump also activated automatically during a normal engine start sequence.

Low fuel pressure from either the engine driven pump or the standby pump was indicated by the illumination of the left or right fuel pressure low (L or R FUEL PRESS LOW) warning annunciator.

The fuel leak in the engine driven pump supply line was stopped by maintenance personnel soon after the incident, by manually closing the fuel shut-off valve positioned on the front of the fuel collector tank. There was no mechanical method of isolating the leak from the motive flow line. The fuel flow from this line was temporarily stemmed by the fitting of a rubberised electrical wiring loom clamp over the hole in the line.

The electrically activated right engine firewall shut-off valve was found to be in the open position.

Electrical

The landing light system operating voltage was 28 volts DC. The 450 watt landing light receives its power from the K11 relay, positioned in the rear of the right engine nacelle area. The relay contactor switching wiring was protected by a 10 amp circuit breaker positioned in the aircraft underfloor area. The electrical wiring leading to and from the K11 relay to power the landing light, was protected from a prolonged overcurrent situation by a 35 amp mechanical indicating, enclosed link, current limiting fuse. This device was utilised to allow a transient high current draw that would occur during the landing light initial illumination. Examination of the fuse revealed that the mechanical indicating pin had triggered. This indicated that the internal fusible link had melted.

The landing lights were normally switched on during descent at the transition altitude of 10,000 ft. This was done as a part of the operator's transition checklist actions. In this instance, the crew advised that the lights were turned as the aircraft descended through 11,300 ft. No abnormal operation of the lights was noticed at any time, with good illumination of the runway for landing.

The electrical wiring was examined and found to be of the correct specification as detailed by the manufacturer. The wiring had a copper core with the insulation surrounding the wire manufactured from white extruded ethylene-tetrafluoroethylene copolymer (ETFE). The surface of the wiring and aluminium fuel line tubing was microscopically examined, with no evidence found of any rubbing on or around the arcing points.

The aircraft manufacturer indicated that the normal method for the positioning and securing of the electric wiring, in areas such as the right-wing equipment bay, was by utilising plastic cable ties (See Fig 3). The ties would be routed through lengths of plastic tubing that acted as cable stand-offs. These were to used to securely position the electrical wiring, and ensure that it did not come into contact with the adjacent fuel lines.

An inspection of other Beechcraft 1900 aircraft in the operator's fleet revealed cable tie and tubing stand-offs securing the landing light wires. These were attached around the fire sleeving on the wing de-ice boot pneumatic lines in the forward area of the bay.

The inspection of the area around the motive flow fuel line on the accident aircraft, revealed that one of the two landing light wires was in contact with the surface of the fuel line. No plastic stand-offs were fitted to space the landing light wiring away from the fuel line. There was however, evidence of a soot-covered imprint of a plastic cable tie on the surface of the fire sleeving (See Fig 4). This fire sleeving surrounded the adjacent wing de-ice boot pneumatic line.

The remains of another plastic stand-off, on the nearby positioned standby fuel pump power wiring, was still evident (See Fig 5).

The aircraft had been subjected to severe hail damage in 1995. During the repairs following this damage, the right-wing leading edge de-ice boots were removed and the pneumatic de-ice lines were disturbed.

The landing light wiring, positioned above the damaged main fuel supply line, was manufactured longer than required. This excess wiring had then been doubled back on itself and tied, with a cable tie, along the main wiring loom into this area. This wiring had also been in contact with the fuel line.

When examined the contacts on the K11 landing light relay exhibited signs of arcing due to excessive 'contact bounce'. 'Contact bounce' is an oscillation of the relay contacts. This condition can be exaggerated as a result of the effects of heat and in-service wear on the springs and latches that control and damp the relay contact movement. With excessive 'contact bounce' present, it is possible for the wiring served by the relay to heat up due to a continually higher than normal current flowing through the wiring. Following removal of the landing light wiring insulation by the ATSB, there was evidence seen of excessive heat on the wiring surface. Plastic deformation of the wiring's ETFE insulation was noted at the point of arcing on the fuel line positioned at the front of the bay.

Fire

The fire damage was most severe in the rear of the wheel well area, this was evidenced by the melted aluminium alloy panel, the distorted wheel well surrounding structure and some destroyed ETFE wiring insulation.

The fuel, from the leaking equipment bay lines, had flowed along the face of the wing spar towards the wheel well area as the amount of fuel increased. The fuel was then able to flow onto the top of the right main gear up position indicator switch, through a hole in the inner fender assembly panel immediately above. The wheel well area was open to the airflow and to the propeller wash at the rear lower end of the inner fender panel.

Air was also drawn from behind the fender panel by the inverter cooling fan positioned in the rear of the engine nacelle area. This cooling air flowed from the wheel well through the rear of the equipment bay, and was ducted along under the right side of the engine nacelle cowling. The duct exhibited signs of heavy sooting and some of the inverter cooling fan plastic blade tips had melted.

The area at the rear of the right-wing equipment bay, through which the inverter cooling air was drawn, was the most heat-affected area of the bay. Some of the ETFE wiring insulation in this area was completely burnt away. The forward end of the bay, in the area of the other fuel leak, exhibited some wiring damage and medium to heavy sooting. In this area there was also evidence of 'washing' of fuel against the upper access panel (See Fig 6). The wiring and components that were immediately adjacent to the fuel leak in the area were not as heat affected as in other parts of the zone.

View of upper surface of right wing, showing fuel 'washing' on upper access panel

A typical hydrocarbon fuelled ground fire would burn at a temperature in the range of 870 ⁰ C to 1093 ^oC. An inflight fire, with the added oxygen, would burn in excess of 1093 ^oC, often up to 1371 ^oC and higher. The aluminium alloy in aircraft becomes plastic at 454 ^o C and melts at about 677 ^oC, while the extruded ETFE insulation on the electrical wiring, melts at approximately 300 ^o C. The cable ties are made from either Teflon or nylon and have a similar melting point of 280 ^o C to 300 ^oC

Engine isolation and fire extinguishing system The aircraft was equipped with an engine isolation and fire extinguishing system that was activated by the operation of a fire emergency tee handle. The operation of the fire handle cuts fuel to the selected engine and arms the engine fire extinguisher bottle. The pilot can then discharge the fire extinguisher by depressing an instrument panel mounted switch.

During the shutdown of the aircraft prior to passenger evacuation, the flight crew had activated the engine fire handles and attempted to discharge the right engine fire bottle several times. The fire bottle, however, had not discharged and the fire wall fuel shut-off valve had not closed. An inspection of these emergency systems revealed that the components had not operated because of fire damage that had occurred to the electrical wiring to these components. The right side firewall shut-off valve circuit breaker was found to have tripped during the incident. Regardless, the operation of the system would not have had any effect in this instance, due to the fire being in an area outside the engine fire zone.

Following an inspection of the manufacturer's maintenance procedures for the aircraft type, it was discovered that there was no procedure for determining the serviceability of the fire bottle activation system that ensured there was sufficient voltage at the fire bottle electrical connection to activate the bottle. This has been brought to the attention of the aircraft manufacturer.

1. The ADC did not adequately scan the runway prior to issuing a takeoff clearance to the crew of the Saab 340 or immediately before the takeoff was commenced.
2. The ADC forgot about a conditional clearance issued to the crew of the B767 to cross the runway at taxiway Lima.

In establishing that the take-off path of an aircraft was unobstructed, controllers were required to make two separate visual observations of the take-off path; one before issuing the take-off clearance and another before take-off was commenced. In addition, controllers needed to have a high level of situational awareness about the movement of other aircraft on the airfield, particularly aircraft subject to conditional clearances to cross or enter an active runway given to aircraft under the control of the SMC. In this particular incident, the controller relied on short term memory to maintain awareness of the clearance issued to the B767.

Memory prompts can assist controllers to maintain situational awareness. Items such as pens, blank flight progress strips or the like were commonly used by controllers to act as memory prompts, but their use was inconsistent in application. Use of some form of memory prompt in this particular incident may have helped to maintain the controller's situational awareness and enhanced the effectiveness of the controller's visual scanning of the take-off path.

The aerodrome controller (ADC) had given a conditional clearance for a Saab 340 to line up on runway 16R behind a landing Boeing 737 (B737). The ADC then gave the surface movement controller (SMC) a conditional clearance for a Boeing 767 (B767) to cross runway 16R at taxiway Lima when clear of the landing B737.

The SMC issued the clearance for the B767 to cross the runway as the B737 vacated the runway at taxiway A4. The ADC observed the B737 vacate the runway at taxiway A4 and cleared the Saab 340 for take-off. The pilot of the Saab 340 rejected the take-off clearance and advised the ADC that there was a B767 crossing the runway.

The Manual of Air Traffic Services (MATS) 6-2-3 paragraph 31 stated:

"Before clearing an aircraft for take-off, and immediately before the take-off is commenced, the tower controller shall make a visual check from the control tower to determine, as far as practicable, that the take-off path is not obstructed." The ADC made a visual check of the runway, however, he only scanned between the runway 16R threshold and the point where the B737 was vacating the runway at taxiway A4. The ADC did not continue the visual check through to the upwind end of the runway. The B767 was crossing the runway at taxiway Lima, which was between taxiway A4 and the upwind end of the runway. The ADC had forgotten about the conditional clearance given to the SMC for the B767 to cross the runway.

There was no standard practice in Australia for the use of "blocking strips" or "memory prompts" by controllers to alert them of the presence of aircraft not under their direct control crossing or entering an active runway. In this particular incident, the ADC did not use, nor was he required to use, a memory prompt to remind him of the conditional clearance given to the SMC for the B767.