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

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

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

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

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

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

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

Factors

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

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

Safety action

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

FACTUAL INFORMATION

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

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

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

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

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

ANALYSIS

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

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

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

SIGNIFICANT FACTORS

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

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

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

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

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

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

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

SIGNIFICANT FACTORS

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

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

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

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

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

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

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

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

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

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

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

On entering the circuit at Moruya the pilot obtained an unsafe indication of the nose landing gear, after selecting the landing gear down. Ground observers reported that the nose landing gear was not in the full down position, however both main landing gears appeared to be down. The pilot recycled the landing gear, but this was unsuccessful and resulted in an unsafe indication for both the nose and right main landing gears. Ground observers reported the nose landing gear was still not fully extended.

The pilot requested emergency services to standby and tried the emergency extension system, but this was also unsuccessful. When the emergency services were in position the pilot carried out a landing, but the nose and right main landing gears collapsed during the landing roll.

Ground inspection revealed a failed hydraulic line in the landing gear extend system. This resulted in the loss of most of the hydraulic fluid, rendering the landing gear system inoperative. The right main landing gear unlocked when the pilot cycled the system, but there was insufficient fluid remaining to retract the landing gear. The emergency system is only effective if used when the landing gear is in the fully retracted position.

FACTUAL INFORMATION

History of the flight

A Boeing 737 (B737) aircraft was tracking via the 320 degree radial of the Hobart VHF omnidirectional radio range (VOR) beacon, on a flight from Melbourne to Hobart. In accordance with standard procedures, Air Traffic Control had transferred the aircraft from Melbourne Sector control to Hobart Tower control.

The Hobart Aerodrome Controller (ADC) cleared the B737 crew to descend to 6,000 ft. This altitude assignment was a restriction due to opposite direction IFR traffic, an Aero Commander (AC500) aircraft which was to track outbound on the Hobart VOR 320 radial.

The AC500 departed Cambridge for Devonport and was on climb to an initial altitude of 4,000 ft for a planned cruise altitude of 8,000 ft. The pilot was advised that there were two B737 aircraft inbound to Hobart on the 320 radial (the second B737 was approximately 20 NM behind the first). He was subsequently instructed by the ADC to climb to 5,000 ft.

At 0916, the ADC carried out a distance measuring equipment (DME) check between the B737 and the AC500 which established that the AC500 was 6 DME and the B737 40 DME from Hobart. The ADC then provided traffic information to both pilots which included a request that each report sighting the other aircraft. While providing the traffic information to the B737 crew the ADC advised that they "should pass [him/in] round about 15 to 16 miles".

At 0918 the B737 crew reported at 24 DME and were advised by the ADC that the AC500 should be in their 1 o'clock to 2 o'clock position and low. Immediately following this transmission, the AC500 pilot reported at 10 DME and maintaining 5,000 ft.

Thirty seconds later, the ADC authorised the B737 crew to track towards a right base for runway 30. He did not specify the time at which they should commence the left turn.

At 0919 the ADC informed the B737 crew that he had the two aircraft in sight, and that as the B737 had turned and was diverging, instructed them to descend to 3,000 ft. He then immediately instructed the AC500 pilot to climb to 6,000ft. The pilots of both aircraft acknowledged their instructions.

The AC500 pilot then reported sighting the B737. This was acknowledged by the ADC but no new instruction was issued other than a request to report sighting the second B737.

The crew of the B737 had not sighted the AC500, but accepted the ADC's judgement that they were clear of that aircraft and commenced a descent from 6,000 ft. At 0919.54 they declared an emergency with a 'PAN' broadcast indicating that the AC500 had passed directly overhead and within 400 ft.

Information later provided by the pilots of both aircraft and a passenger seated on the left side of the AC500 indicated that the AC500 had passed approximately 400 ft above and marginally to the left of the B737 such that their wing tips probably overlapped.

At the time of the confliction, the aircraft were approximately 14 NM from Hobart on the VOR 320 radial, with the AC500 maintaining 6,000 ft. The B737 had just left 6,000 ft in a shallow descent of approximately 600 to 800 ft/min and had commenced the left turn.

Aerodrome controller

The ADC was controlling five aircraft and could not constantly monitor the B737 and the AC500. In accordance with the required standards he initially applied vertical separation of 1,000 ft by maintaining the AC500 at 5,000 ft and the B737 at 6,000 ft. Using binoculars he observed both aircraft and considered that the AC500 was tracking left of the radial. He therefore expected to see the B737 to the right of that aircraft and subsequently assessed that they were just to the right of each other and issued traffic information to that effect.

About 25 seconds after advising the B737 crew that they could turn left off the 320 radial, the ADC assessed that the aircraft had begun the turn and was therefore diverging and providing azimuth separation. He believed that he saw a change in the aircraft profile with only one landing light visible, caused by the nose of the aircraft shielding the other light as the aircraft commenced its anticipated turn. However, the aircraft did not begin the turn until almost a minute later.

Having assumed that the aircraft were diverging, the ADC elected to cancel the vertical separation and issued descent instructions to the crew of the B737. He then instructed the AC500 pilot to climb and was advised by the pilot that he had sighted the B737. The ADC later said that he then automatically transferred the responsibility for separation of the two aircraft to the AC500 pilot and did not continue to monitor their separation. In fact, the ADC did not assign separation responsibility to the AC500 pilot.

Shortly after the occurrence the ADC asserted that the automatic transfer of separation responsibility to the AC500 pilot was valid once the pilot had reported sighting the B737. This was not in accordance with the Australian Manual of Air Traffic Services (MATS) and the ADC subsequently accepted that his position had been incorrect.

MATS provides instructions on the controller's responsibilities when applying visual separation. These instructions include:

- when providing visual separation, controllers shall rely primarily on azimuth;

- corroborative evidence from the pilot of one aircraft on the relative position of another aircraft shall be obtained whenever possible before providing visual separation; and

- visual separation may be achieved when a pilot reports sighting another aircraft and is instructed to maintain separation from that aircraft.

During the period surrounding the occurrence, some phraseologies used by the ADC were not in accordance with the MATS. There were non-standard and/or inappropriate phrases transmitted which led to confusion and added to the airtime taken by the ADC. These included:

- The ADC's advice to the B737 crew, of the opposite direction traffic, was not clear in that he had intended to indicate that the aircraft would pass at about 15 to 16 DME from Hobart, but the crew understood it to mean in 15 to 16 NM from their present position (therefore at about 24 DME). The use, by the ADC, of the non-standard word "him", which the B737 crew heard as "in", in the statement referring to the distance at which the AC500 should pass, contributed to the confusion.

- The ADC, when issuing the instruction for the B737 to divert from the Hobart VOR 320 radial was not specific, in that he said only "CZH you can track towards right base", and did not include a time requirement.

- The ADC's later remark concerning the B737 making a turn and thereby diverging, was not recognised by the crew.

The controller stated that visual separation is a subjective judgement, and, in this case, he was satisfied with the separation provided. He did not enter the details of the PAN radio transmission into the tower log because he did not consider that an incident had occurred. MATS states that such an entry must be recorded, even though subsequent transmissions indicated that the B737 had resumed normal operations within a few seconds of the PAN broadcast.

B737 Crew

As the B737 approached 6,000 ft, it was maintaining approximately 250 kts, and the crew had not yet sighted the AC500. The aircraft was being levelled at 6,000 ft when the ADC informed the crew that he had both aircraft in sight and issued instructions for a further descent to 3,000 ft. They believed that they could descend and turn at their discretion. Consequently, the crew elected to maintain 6,000 ft for a short time while continuing to look for the AC500 in their 1 to 2 o'clock low position as advised by the ADC.

The crew could not recall hearing the ADC's reference to their aircraft having turned left, nor the clearance for the AC500 to climb to 6,000 ft. They considered that transmissions by the ADC had been generally vague and had contained unnecessary chatter.

At approximately 15 DME, and within one minute of the instruction to descend, they decided to continue descent. Earlier in the flight they had expected that the point of passing would be at about 24 DME. However, this was reassessed when at 24 DME the AC500 reported at 10 DME. Confident that the ADC was maintaining separation and that the AC500 must by then have passed, they commenced the descent and the left turn towards the runway 30 base leg. The AC500 then passed close over their aircraft.

AC500 pilot

Although the flight was a single pilot operation, a second pilot (travelling as a passenger) was seated in the right front seat. During the period of the occurrence, the passenger assisted the pilot to monitor the proximity of the other aircraft and to assess possible responses to the situation.

The pilot advised that the aircraft was established on the 320 radial and climbed to 6,000 ft in accordance with the ADC's instructions. At about one minute prior to passing he sighted the B737 and was expecting the ADC to transfer the responsibility for separation to him. This did not occur and the pilot assumed that the ADC continued to provide separation. As the two aircraft came closer (about 20 seconds prior to passing), both he and the passenger observed that the B737 was at about their height. They considered that avoiding action was not necessary as the aircraft was descending and would pass beneath. They assessed that the B737 passed about 400 ft below and slightly to the left.

Although the AC500 pilot said that he was used to seeing other aircraft pass within about 500 ft, he had not seen a jet at that distance before. He commented on the unexpectedly high closing speed of the aircraft.

The aircraft were closing at approximately 7 NM/min.

"See-and-avoid"

Previous BASI reports have described in detail the limitations of the "see-and-avoid" principle in circumstances such as those applying to this occurrence. The time required to detect the traffic, decide upon and execute evasive action, combined with the delay of the aircraft in taking up the commands, can require approximately 8-12 seconds. However, "see-and-avoid" without accurate traffic position alerting is likely to be ineffective.

ANALYSIS

Separation

The controller initially applied vertical separation procedures but reverted to visual procedures when he assumed that the B737 had begun to turn from the 320 radial. Having earlier assessed that the aircraft were to the right of each other, he was satisfied that the left turn he believed had been commenced would provide azimuth separation. However, the required separation did not exist, as the aircraft were being flown on track and the B737 had not commenced the turn until immediately prior to the time of passing.

The pilots were given misleading advice regarding the relative positions of the aircraft. However, having sighted the B737 about one minute before passing, the AC500 pilot did not advise either the ADC or the other crew of the positions of the aircraft. Consequently, the potential benefit of alerted "see-and-avoid" was reduced, with the B737 crew continuing to search for traffic in the 1 to 2 o'clock low position, when the AC500 was directly ahead and at about the same level.

The ADC's judgement that visual separation had been achieved was based on a very short monitoring period. Human visual acuity is degraded when anticipated tracking time and target exposure time are both short. He was providing visual monitoring at distances greater than 15 NM. Without the aid of binoculars, details such as aircraft profile and the number of lights would not be adequately distinguishable. However, using binoculars to see such detail severely restricts the field of view, to the extent that the opportunity of using distinct visual reference cues, such as the attitude of the B737 in relation to the ground or to the AC500, would have been reduced.

Expectation is a powerful influence when information detail is incomplete. In this case, it is possible that the ADC allowed his expectancy to fill in the gaps when, due to other work-related tasks, he was unable to constantly monitor the progress of both aircraft.

Radio phraseology

It is likely that the use of standard, precise phraseology by the ADC would have resulted in less confusion and a greater awareness of the situation by all involved. The ADC had, on previous occasions, been made formally aware of the need for the disciplined use of standard phraseology.

B737 crew

The B737 crew commenced their descent from 6,000 ft within the required time frame. However, the timing of their descent was slightly delayed, reflecting their uncertainty resulting from the ADC's poor application of phraseology and separation procedures. The crew's mis-understanding of the ADC's earlier estimated point of passing together with their inability to visually acquire the traffic, and the vague instruction to turn left, were all potentially distracting. The words "..you can...", used in the instruction, were the subject of some discussion by the crew and were considered by them to mean "when ready". At a time of heightened cockpit workload, these sources of ambiguity may have degraded the crew's ability to assimilate other information transmitted by either the ADC or other aircrew.

It is likely that this environment contributed to the apparent lack of recognition by the crew concerning the ADC's comment that the aircraft had turned and was now diverging. Had the crew recognised the error and corrected the ADC, he may have applied more appropriate separation procedures. However, the crew accepted the ADC's assertion that he was able to visually separate both aircraft.

The instruction to the AC500 pilot to climb to 6,000 ft probably did not appear to be significant to the B737 crew at that time as they assumed that the aircraft had already passed.

The AC500 pilot

Although the pilot was aware that the ADC's traffic advice was incorrect, he did not recognise the value of an accurate position alert to the B737 crew to help ensure their safe passing. It is likely that this was because he believed that the ADC was providing the separation. However, he did not consider questioning that the separation was adequate.

SIGNIFICANT FACTORS

1. The ADC's perception of the relative positions of the two aircraft was incorrect.

2. The ADC used poor and confusing phraseology.

3. The ADC's uncertainty of the rules relating to visual separation by pilots resulted in no positive separation being applied at the time of the occurrence.

4. The pilots of both aircraft missed opportunities to resolve confusion and errors in the ADC's management of the separation of the aircraft.

SAFETY ACTION

As a result of the investigation of this and other occurrences, the Bureau of Air Safety Investigation reviewed aspects of visual separation guidance in MATS.

Airservices Australia have advised that references in MATS to visual separation are to be consolidated into a new section titled 'Visual Separation'. A controller's guide to the application of visual separation procedures is also to be produced.

An Australian registered B767 aircraft arrived at Denpasar (Bali) aerodrome at night, and amid several active thunderstorms. The weather forecast indicated fine weather, but on arrival, Instrument Meteorological Conditions (IMC) prevailed. Inside 10NM from the aerodrome, the crew needed to avoid three thunderstorms which made instrument approaches difficult.

There was no advice to aircrew of the presence and intensity of the thunderstorms on the 'Meteorological Information to Aircraft in Flight' (VOLMET) or the Automatic Terminal Information Service (ATIS). Air traffic control did not provide any updates on such storms.

Navigation was made more difficult as the main aerodrome navigational aids were overdue for calibration and the relevant NOTAM indicated they were to be used 'with caution'. The crew made two missed approaches before successfully landing at the destination. The Bali VOR approach aid had been reported to be up to 12 degrees out of alignment, but air traffic control were able to have a ground technician ensure that it remained within ground tolerances to permit instrument approaches in IMC.

The investigation revealed that the aircraft engaged in performing the flight testing of the Bali navigational aids had been placed unserviceable the day before it was due to commence testing at Bali. The aids were to be rescheduled for testing as a priority, once the aircraft was serviceable.

Safety Action

As a result of the investigation, air traffic controllers were reminded by their local air traffic services management, of their responsibility in providing accurate weather updates to aircrew. Controllers were also reminded of the requirement to provide such weather information on the ATIS and VOLMET services.

On request from Indonesian ATS management, Australian operators were asked to report any discrepancies in the navigational aids to air traffic control by radio at the time of the occurrence, so that ground technicians can investigate the cause immediately.