International

FACTUAL INFORMATION

History of the flight

The Boeing 747 aircraft was operating from Cairns to Narita, cruising at flight level (FL)310. The flight is normally a daylight service but because the departure was delayed for 3 hours, the latter part of the flight, including this incident, was in darkness. Shortly after the aircraft passed Vasko, a position reporting point located at 25 degrees N and 142 degrees 02 minutes E, it encountered severe turbulence which lasted for a period of approximately 12 seconds. The encounter resulted in injuries to some unrestrained passengers and cabin crew and disruption of the rear cabin due to unsecured meal trolleys. The encounter occurred approximately 650 miles south of the destination. The pilot in command was in the crew rest section of the aircraft and the co-pilot was the pilot on watch, supported by the third pilot and flight engineer.

The co-pilot said that the first indication he noted was when the aircraft pitched up and climbed about 300 ft. He immediately switched the seat belt signs on and the flight engineer switched on the ignition and nacelle anti-ice. The aircraft then encountered the turbulence which the crew thought lasted for about 5 seconds. The autopilot remained engaged throughout the encounter. After the encounter, the co-pilot was informed by a cabin crew member of the situation in the rear cabin. As there were no radar returns in the immediate vicinity of the aircraft that may have indicated the possibility of further turbulence, the co-pilot turned off the seat belt signs and the pilot in command returned to the flight deck.

Approximately 20 minutes before the occurrence, at the direction of air traffic control, the aircraft descended from FL350 to FL310 for traffic separation. The co-pilot said that at that level the aircraft was in and out of cloud but there were no radar returns indicating any weather on the aircraft's track. The consensus of opinion from the crew was that the aircraft was in clear air at the time of the encounter and that there was a complete overcast about 500 ft above their cruising level. However, a few minutes before the encounter, there were returns indicating isolated buildups approximately 40 NM ahead and 15 NM to the right of track.

The co-pilot believed the wind velocity at FL310 at the time of the occurrence was north-westerly at 4-10 kts. This was consistent with the forecast wind velocity. After the encounter, the aircraft continued to its destination where the more seriously injured passengers and crew received medical attention.

Injuries to persons

At the time of the encounter, the cabin staff were just commencing a meal service. Injuries were sustained by six cabin staff and 24 passengers, most of whom did not have their seat belts fastened. The severity of the encounter was such that some passengers, cabin crew and meal trolleys hit the cabin ceiling and then landed heavily back on the floor. This resulted in some serious injuries being sustained, including bone fractures, lacerations, neck and back strains, a dislocated shoulder and shattered teeth. On arrival at the destination, three passengers and one flight attendant were admitted to hospital.

Damage to aircraft

A severe turbulence conditional check, completed in accordance with the maintenance manual, revealed no structural damage was sustained by the aircraft. There was minor superficial damage to the cabin interior including three damaged passenger service units, three damaged oxygen masks and damaged meal trolleys. The aircraft was returned to Sydney the following day where it was subjected to further inspection and minor maintenance, and then returned to service.

Meteorological information

Flying conditions both before and after the encounter were smooth. Examination of Bureau of Meteorology satellite imagery indicated there was a typhoon (Tropical Storm Dan) centred to the east of the aircraft's track. The aircraft traversed the western flank of that system and encountered an isolated area of vertical development that was not showing on aircraft radar. Information on the storm was included in the pre-flight meteorological briefing material received by the crew.

An analysis of the encounter was completed by the Bureau of Meteorology Research Centre (BMRC). A report of their investigation was published as BMRC Research Report No 58. In summary, the BMRC report concludes that the incident was associated with a developing squall line within an outer spiral band or "feeder band" of a developing typhoon. Rather than being "clear air turbulence" as such, the incident is categorised as turbulence near thunderstorm tops (TNTT). The report goes on to say that based on current knowledge and operational procedures, meteorologists cannot predict the specific location for this type of turbulence.

However, from present knowledge of tropical convection, it seems likely that typhoon or tropical storm outer spiral bands would be a preferred location for such turbulence. Such bands are evident on satellite imagery but are not detectable on current aircraft radar systems. The squall line being in a stage of rapid development was probably a contributing factor in this case, as likely locations for such rapid development of turbulence are the intersections of cloud arcs with squall lines.

Flight recorders

The aircraft was equipped with a Lockheed 209E digital flight data recorder (DFDR). The recorded data showed that the aircraft left FL350 on descent to FL310 at 1045 UTC. At 1104 UTC, vertical acceleration values of +1.58g and -0.43g were recorded. Pressure altitude variations during this period were +400 ft to -100 ft from the cruising level. At the time of the encounter, the aircraft was cruising at Mach 0.84 with the B autopilot engaged in the command mode. The duration of the encounter was approximately 12 seconds with smooth flight conditions prevailing for several minutes both before and after the event.

ANALYSIS

The turbulence encounter

Because the type of turbulence encounter was one not detectable by aircraft equipment, the crew had no warning of the impending encounter and were therefore unable to take any avoiding action. 

Injuries

The injuries occurred because there was no warning of the turbulence and hence no specific measures had been taken to protect against it. The activation of the seat belt signs, albeit as soon as there was evidence of unusual aircraft behaviour, came too late to allow passengers and crew time to fasten their seat belts.

SIGNIFICANT FACTORS

1. The aircraft was experiencing smooth flying conditions and there was no indication of an impending severe turbulence encounter.

2. There had been no preparation in the cabin for a severe turbulence encounter.

3. The turbulence encountered (TNTT) was of a type that was not detectable on aircraft radar systems and could only be identified on satellite imagery.

SAFETY ACTION

Safety action by the operator

As a result of this investigation, the operator's safety department made a number of recommendations.

1. Medical matters

Three recommendations made in respect of medical equipment and procedures. When cabin staff were trying to assist injured passengers, they encountered some difficulties locating appropriate medical supplies and opening first aid kits. In addition, the operator's investigation revealed that some crew were not aware that a company duty doctor was available at all times to provide advice to the crews of aircraft in flight. Company safety department recommendations in respect of these matters were:

i. [The company's] Medical Department should ensure the first aid kits are easy to open. The tape should have a tab on it so it can be opened easily.

ii. The medical amenities should be easy to locate. The drawer that contains such items should be placarded.

iii. Crew should be made aware that a [company] duty doctor is available at all time to help them and to provide any advice whilst they are in flight.

2. Technical matters

During this investigation it was noted that the cabin floor was not fitted with "mushroom" devices which are used to secure the meal trolleys to the floor when meals and/or refreshments are being served. When the aircraft encountered the turbulence, some unsecured trolleys hit the roof. In such circumstances the trolleys become a potential source of injury. Some [company] aircraft did have these fittings but they were removed some time previously. In this particular incident, "mushroom" devices would not have prevented the trolleys lifting off the floor because they were being moved at the time of the occurrence. 

The [company's] Safety Department recommended that the Engineering and Maintenance Department provide a costing for fitting the entire fleet with cabin floor mushrooms. Upon receipt of that information the company will carry out an analysis on the feasibility of retrofitting this equipment.

The operator's report also recommended that the Safety and Flight Operations Departments form a Turbulence Committee to:

i. review past occurrences and data,

ii. assist internal customers with implementing emergency plans, and

iii. review reporting procedures to ensure all injuries are reported via air safety incident reports so as to allow correlation with workers compensation and human resources records.

Safety action by the Bureau of Meteorology Research Centre (BMRC)

The BMRC Research Report No. 58 suggested that the BMRC take the following steps to improve its understanding of gravity-wave type turbulence associated with tropical convection:

(i) develop an infrastructure to collect and process both meteorological and flight recorder data for all turbulence incidents on air routes used by international regular public transport operators servicing Australia. This would facilitate statistical analyses of frequency and location of incidents and case studies to identify key large-scale conditions leading to severe turbulence;

(ii) initiate correspondence with several international research institutions (with expertise in aviation meteorology, tropical convection, typhoons and diagnosis of clear air turbulence operational numerical models) with which the BMRC has long-term working relationships, as part of further investigation of the incident;

(iii) present a report on the meteorological conditions leading to the incident to the American Meteorological Conference on Aviation, Range and Aerospace Technology;

(iv) improve BMRC staff knowledge of flight instrumentation and data recorders, through interaction with aircraft operators and overseas meteorologists and engineers who work with these data; and

(v) investigate the development of numerical algorithms to diagnose the conditions conducive to both spiral band development and upper tropospheric propagation of gravity waves, based upon the current Bureau of Meteorology's operational numerical analysis and prediction models.

Copies of BMRC Research Report No. 58 can be obtained from: BMRC GPO Box 1289K MELBOURNE, Vic. 3001

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.

Report not released due to no IP comment from the Indonesian agency on this joint investigation report.

ASOR hard copy held on occurrence file.

Report not to be released without the approval of the Director or a DD.

Signed

Alan L Stray

Deputy Director Investigations

6 July 1998

FACTUAL INFORMATION

An international B747 flight was proceeding at flight level (FL) 350 from Melbourne to Singapore via Curtin and air route A576, exiting the Australian Flight Information Region (FIR) at ATMAP. Prior to reaching Curtin, the crew were advised by Brisbane air traffic control (ATC) that, due to another aircraft on the same route and level three minutes ahead, FL 350 would not be available. The pilot in command was absent from the flight deck on an authorised rest break leaving the first and second officers controlling the aircraft.  The crew's intention was to eventually cruise at FL 390 but the operational performance of the aircraft at this stage of the flight precluded such climb. Several alternatives were discussed with ATC and eventually an option to climb to a non-standard level (FL 370) was accepted, with an understanding that the aircraft would have to climb to FL 390 by the FIR boundary.  At this point ATC issued a climb instruction to FL 370 only, thus ensuring separation with the preceding B747. The aircraft climbed to, and maintained, FL 370 prior to Curtin.

Approaching Curtin, the crew rotated positions as the pilot in command returned from a rest period and the first officer vacated the flight deck. The second officer remained on the flight deck and continued to operate the radios while the pilot in command assumed the duties of the flying pilot. The crew carried out an information brief at the changeover but could not remember the exact details regarding the level change proposals.

Shortly after the crew had reported the Curtin position with an estimate for ATMAP, the Brisbane sector controller notified the position report and estimate to the Perth flight service operator on international HF radio and coordinated a change of level to FL 390 with Bali Control. The controller then issued a clearance to the crew, advising: "When ready climb to FL 390, requirement reach FL 390 by ATMAP". The second officer correctly read back the level and requirement.

On transfer from Brisbane Control to the Perth HF operator, the crew reiterated the requirement to be at FL 390 by ATMAP. However, the aircraft maintained the current level of FL 370 and subsequently entered the Indonesian FIR at the wrong level. The crew reported maintaining FL 370 at ATMAP to Bali HF and again on first contact with Bali Control on VHF (approximately 15 minutes later).  It was at this point, when the aircraft was identified on radar, that the level was first queried by ATC.  The Bali controller then requested confirmation of the original coordination message from the Australian controller, who confirmed that the aircraft had been required to reach FL 390 by ATMAP.

ANALYSIS

The crew remarked that there was nothing exceptional with respect to the conduct of the flight apart from some problems experienced maintaining situational awareness.  The crew thought the traffic with which they were conflicting at FL 350 was a British Airways aircraft when in fact it was Thai International.  The British Airways aircraft was on a parallel route which would eventually converge with A576 but, at this stage, was well clear of the incident aircraft. The Thai aircraft had reported at Curtin three minutes earlier than the Qantas B747, but this report was not remembered by the crew.  This aspect was not considered to be a significant factor in the incident. 

However, during the investigation it became evident that a lack of situational awareness could ultimately affect pilot actions and that in the future, the introduction of new technology such as automatic dependent surveillance (ADS) might further reduce the ability of aircrew to develop and maintain an air picture. Should separation break down under such circumstances, one of the secondary methods of minimising the likelihood of a collision or near miss would be removed.

The second officer believed he noted the level requirement in the aircraft deck log, but he did not remember referring to the log to confirm the requirement. As a result of his understanding of ATC requirements given at the crew information brief following his return to the flight deck, the pilot in command believed the requirement was to reach FL 390 by ILDAM (a position reporting point in Indonesian airspace) and was thus unconcerned that the aircraft was maintaining FL 370 on entering the adjacent FIR. However, he was the flying pilot at the time that the ATC clearance requiring climb to FL 390 by ATMAP was issued.

The pilot in command and the second officer agreed that the clearance had been correctly issued and read back. They could offer no explanation for their failure to comply with the conditions of the clearance.

Currently, there is no specific company procedure, other than good crew resource management practices, for flight crews to record and action amended clearances or those containing a future requirement. However, the crew members believe there are a number of means available to aircrew to record clearances. Generally, these are used at the discretion of the individuals concerned.

Indonesia had issued NOTAM A 0008/96 on 3 January 1996 which required crews to report their boundary position for the Bali FIR to Control on VHF radio.  However, this NOTAM had not been received in Australia by the date of the occurrence.  Therefore, the crew (and Perth HF) had no reason to change previous standing instructions to contact Bali on HF at the boundary.  This factor had the potential to remove a safety net in that the Bali controller had a delay in receiving the ATMAP position report which required relaying through the Bali HF operator. The investigation was unable to determine why the NOTAM was not received in Australia.

SIGNIFICANT FACTORS

1. Crew resource management proved to be ineffective in that the crew did not climb the aircraft to FL 390 by ATMAP.
2. The lack of a standard operating procedure to record and act on clearances did not provide a means of alerting the crew when a future action was required.

SAFETY ACTION

As a result of the investigation the company has:

1. Implemented a flight standing order (FSO) which will:

• initiate the use of the flight management computer as a reminder tool for clearances;
• highlight the requirement for flight crew personnel to ensure conditional clearances are brought to the attention of other crew members; and
• instruct crew members to notate all enroute clearances.

2. Initiated an educational program, via the check-and-training system, highlighting aspects outlined in the FSO.

3. Proposed the publishing of a safety magazine article detailing the crew's perspective of the incident.

As an additional result of the investigation, the safety deficiencies in regard to crew situational awareness and the potential problems of introducing Automatic Dependent Surveillance have been referred to the Bureau's Safety Deficiency Section for further analysis. Any resulting safety output made by the Bureau will be published in the Quarterly Safety Deficiency Report.

Factual Information

GIA829 was maintaining flight level (FL) 350 on air route G326 and was estimating the flight information region boundary at ONOXA at 0330 UTC.  This information was correctly coordinated by Brisbane sector control to Bali control.

GIA899 was maintaining FL 330 on air route A576 and had passed CURTIN at 0245 with an estimate for the boundary at ATMAP of 0347.  This information was also correctly coordinated with Bali control and included the specific indication of a non-standard flight level.

During the coordination process, Bali control advised that they could not accept GIA899 at the non-standard level (FL 330) and required that aircraft at FL 350.  Brisbane sector accepted this requirement and after checking his flight progress strips, the controller calculated that there would be 13 minutes between the two aircraft at Bali (Den Pasar).  As the required standard is 10 minutes, he then instructed the crew of GIA899 to climb to FL 350.

At 0329 the Brisbane controller was checking his flight strips and realised that the flight plan time interval for GIA899 between ATMAP and Bali was approximately 10 minutes in error and the separation between the two aircraft was in fact only 2-3 minutes at Bali.

When the flight times were corrected, it was realised that GIA899 and GIA829 were already within the zone of conflict and that a breakdown in separation standards had occurred.

The Brisbane controller immediately initiated coordination with Bali control, but it was some minutes before contact was made.  When coordination was completed the Bali controller accepted responsibility for re-establishing separation and commenced distance checks from the two aircraft.

It is not known exactly which separation standard was affected by Bali control.

Analysis

When Bali control made the request for both aircraft to be at FL 350 it was based on the previous reported positions of the aircraft and the flight planned times from those positions to Bali.  In the case of GIA899 this time interval was incorrect and contained an approximate 10 minute error.

As both Brisbane and Bali control were using the same flight plan details, it is likely that both controllers considered that a 10 minute separation standard existed.  It was only when the Brisbane controller checked his time intervals against those being commonly used by other aircraft during the period, that the error was noticed.

The computer aided strip printing system only provided a proportional breakdown of the block times notified on the flight plan.  In this case, the first block times were correct and there was no trend to alert control to any time interval error.

There was also a table of estimated time intervals provided on the control console for controller reference.  This table had several erroneous time intervals included in its data and was commonly not used by controllers.

Findings

1. The flight plan for GIA899 contained an erroneous time interval.
2. The table of estimated time intervals held at the Brisbane control console contained several errors.
3. Bali control was unable to accept GIA899 at a non-standard level (FL 330).
4. Both the Brisbane and Bali controllers had information that indicated that a 10 minute separation standard existed.
5. All coordination between Brisbane and Bali was carried out in accordance with the Letter of Agreement.
6. Brisbane control issued a clearance for GIA899 to climb to FL 350 in accordance with Balis requirements.
7. The actual separation was approximately 2- 3 minutes.
8. A breakdown in separation standards occurred.

Significant Factor

The flight plan details for GIA899 were errant, in that they contained an incorrect time interval between ATMAP and Bali.

Safety Action

As a result of the investigation, Brisbane ATS management have removed the erroneous time interval table from the console.  It has been replaced with a table of average times for each type of aircraft using particular air routes.

Report not released due to no IP comment from the Indonesian agency on this joint investigation report.

ASOR hard copy held on occurrence file.

Report not to be released without the approval of the Director or a DD.

Signed

Alan L Stray

Deputy Director Investigations

6 July 1998

Two aircraft, at the same level on air route A585, lost separation standards assurance when the controller did not apply the appropriate standard. The lead aircraft was a RAAF VIP Boeing 707 carrying the Australian Prime Minister. The trailing aircraft was a scheduled Qantas passenger service.

The Brisbane Sector 12 controller applied a 10-minute separation standard instead of a 15-minute Oceanic standard when he allowed the lead aircraft to climb to the same level as the trailing aircraft. Later, the controller assured Perth Sector 1 controller that the 10-minute separation standard would be monitored and a distance standard established if necessary.

The separation was reduced to eight minutes at Port Hedland when the lead aircraft, Aussy 360 arrived one minute later than ETA and QFA10 arrived one minute earlier than ETA. The controller did not establish a distance standard (20 NM on DME or 30 NM RNAV) when the aircraft entered the CTA, 120 NM north-west of Port Hedland.

The controller applied an incorrect separation standard of 10 minutes to the aircraft at DOMOM whereas the oceanic standard was 15 minutes. He also did not establish a distance standard between the two aircraft as agreed with the Perth Sector 1. The controller could not explain the omissions. However, he was on a late-night shift with little traffic under his control. He may have been in a state of low arousal and was unaware of the errors.

Circumstances

ANA914 was northbound on route B462 and cruising at FL310.  At 0130 UTC, the Brisbane Sector 10 controller coordinated with Moresby Control ANA914 estimating position APAVO at 0221, FL330 (the aircraft was at FL310 and maintained that level throughout the period of the occurrence). The Moresby controller read back FL330. The Sector 10 Flight Progress Strip for ANA914 showed the aircraft's level as FL310. There was no reference to FL330 on the strip. The Sector 10 controller did not include the words non-standard in the coordination, as was required by standard procedures, and the Moresby controller did not query this omission.  At approximately 0200, there was a shift change at the Sector 10 control position. There was nothing to indicate to the new controller that anything other than FL310 had been coordinated to Moresby Control.

At 0210, Moresby Control coordinated the departure of ANG3 Port Moresby for Brisbane on route B462 at 0208 on climb to FL370, estimating APAVO at 0252. The controller also said that she would provide separation with ANA914. She had planned to provide this separation by maintaining ANG3 at FL310, a level she understood to be below ANA914.  She would then climb ANG3 to the planned level, FL370, after the two aircraft had passed.

Information from the Department of Civil Aviation, Papua New Guinea, indicated that, at 0221, Moresby Control contacted ANA914 advising ANG3 as opposite direction traffic passing beneath ANA914 at an estimated time of 0226, and requesting ANA914 to report sighting and passing the traffic. ANA914 requested Moresby Control to repeat the information. This was done but the response from the ANA914 pilot indicated that the message had not been understood.  Two further attempts were made by the controller to convey the information but the response from ANA914 continued to indicate that the message had not been understood.

At 0224, the pilot of ANG3 asked ANA914 his level. ANA914 responded that he was at FL310, had traffic in sight, and was descending.  The crew of ANA914 was alerted to the confliction with ANG3 by the aircraft's TCAS equipment. ANG3 was not equipped with TCAS. However, the crew of ANG3 sighted ANA914 passing below their aircraft and estimated the vertical separation to have been less than 500 ft. The required vertical separation standard was 2000 ft.

The aircraft level (FL310) written on the flight progress strip for the aircraft had not been ticked (in accordance with normal procedures) by the Sector 10 controller to indicate that coordination had been completed. No other aircraft in the Sector 10 control area was at FL330. The basis for the controller coordinating FL330 was, therefore, not established. However, he did report what, in his view, were minor but irritating difficulties in operating the telephone link to Port Moresby to initiate the coordination. There was also some evidence of the controller suffering fatigue.

Discussion

The agreement between the air traffic control agencies of Australia and Papua New Guinea allows for non-standard levels to be used only when prior co-ordination between controllers has been carried out.  Therefore, the use of FL330 for ANA914 was contrary to this agreement as no prior co-ordination had been initiated.  The fact that the phrase non-standard was not used in the co-ordination should have provided an additional cue that an error had been made. Beyond this point, however, in the procedural environment in which the aircraft were operating, the sole remaining element in the safety net was TCAS on ANA914.

The difficulties experienced by the Port Moresby controller in communicating the opposite direction traffic to ANA914 highlight the language and comprehension problems which can arise in the control of international air traffic.  TCAS takes on added importance in such situations.

Significant Factors

1. The Sector 10 controller may have experienced some frustration operating the telephone link to Port Moresby.
2. The Sector 10 controller may have been fatigued.
3. The Sector 10 controller coordinated an incorrect level and did not use the prefix non-standard to describe that level.
4. The Port Moresby controller did not query the omission of the prefix non-standard when reading back the coordination.

Safety Action

As a result of the TCAS implications of this occurrence and as similar implications were found to be present in occurrence B9501346, the Bureau considers it is of significant safety value to reproduce interim recommendation IR950117 in this report. IR 950117 was addressed to the Civil Aviation Safety Authority on 6 June 1995.

IR 950117

The Bureau of Air Safety Investigation recommends that the Civil Aviation Authority:

1. mandate the fitment and use of an Airborne Collision Avoidance System (ACAS) in all aircraft engaged in Regular Public Transport (RPT) operations;
2. consider the requirement for the fitment and use of a suitable ACAS in other aircraft engaged in the carriage of passengers for hire or reward;
3. review the requirements for the carriage and activation of transponders with the objective of maximising the effectiveness of ACAS;
4. mandate the standard of ACAS equipment to be carried in each aircraft classification;
5. set a timetable for the introduction of ACAS equipment; and
6. ensure that air traffic services officers are given adequate and timely education and continuation training in the capabilities and operational impact of ACAS equipment.

The B767 was maintaining FL280, enroute from Denpasar to Singapore. As the aircraft approached SUMBU, at the junction of the A576 and W18 airways, the crew received a traffic alert from the aircraft's Traffic Alerting and Collision Avoidance System (TCAS). The crew checked the sector indicated by the TCAS and sighted another aircraft in their 2 o'clock position, at a range of about five miles. At the same time, the TCAS issued a resolution advisory "climb" command.

The captain climbed the aircraft as directed and the other aircraft passed about 200 feet below them. After several requests to Jakarta Control, the conflicting traffic was identified as a B737 enroute from Banjarmasin to Jakarta, also maintaining FL280.

The No. 1 hydraulic system failed soon after take off. The flaps retracted to 6 degrees and the right main landing gear warning light illuminated. The pilot declared an emergency and the aircraft was held until emergency services were in place. Emergency landing gear extension was successful, and a normal landing followed, but without nosewheel steering, requiring the pilot to use asymmetric braking.

Subsequent investigation revealed the No. 1 engine hydraulic pump pressure outlet elbow had failed, allowing a complete loss of fluid from the No. 1 system. The operator has consequently revised the inspection criteria for all hydraulic system elbows fleetwide.