The thrust reverser fault light on the pilot' overhead panel illuminated when the aircraft was approaching top of climb out of Darwin. The crew completed the required check list items and elected to return to land at Darwin. Maintenance locked out the thrust reverser and the aircraft flew to Adelaide where the engine accessory unit (EAU) was replaced.

Thrust reverse control system

The thrust reverser control consists of a thrust reverser isolation valve and a directional control valve for each reverser. Each isolation valve is opened by switches. These switches sense motion of the control stand quadrant to command reverse thrust, and low altitude or compression of the right main gear for normal operation. Also, if a reverser sleeve is sensed to be not fully stowed, the isolation valve is opened and the directional control valve is commanded to the stow position.

Illumination of the reverser light in flight indicates that the reverser isolation valve is open and the directional control valve is in the stow position or vice versa. The light will also illuminate if the stow enabling relays for each sleeve disagree for more than two seconds.  The reverser light illuminates during normal stow and trips the master caution after approximately 12 seconds.

An open thrust reverser isolation valve will not, by itself, permit the reverser to be deployed in flight: the directional control valve requires ground logic and movement of the reverse thrust lever to move to the deploy position.

Similarly, a directional control valve in the deploy position will not, by itself, permit the reverser to be deployed in flight; the isolation valve also requires ground logic and movement of the reverse thrust lever to open.

System serviceability

The thrust reverse indication system has had a history of intermittent illumination of the overhead panel thrust reverser fault light. The manufacturer has addressed many of the causes through design changes such as the introduction of a spring-loaded proximity sensor, improved thrust reverser control switches located in the isle stand as well as introduction of a six-light engine accessory unit which facilitates trouble shooting.

However, many operators still report problems with troubleshooting the system. These problems have led to a high rate of removal of the EAU, testing of which was unable to confirm any unserviceability within the units. In 1993 the manufacturer introduced a sixteen light EAU capable of monitoring the individual state of each of the thrust reverser indication proximity sensors.

Continuing erroneous fault light illumination was traced to a certain batch of relays fitted to the EAUs. These were failing because of chemical/thermal corrosion of the coil wire, or insufficient clearance between the case and the armature, or cold welding of the relay contacts.

Operators engineering action

The operator is removing the suspect relays on a campaign basis and is having the improved EAU fitted to current delivery aircraft. However, the improved EAU will not be retrofitted to the existing fleet.

A modification that introduces an independent method of locking the stowed thrust reverser is being progressively introduced. So far, the operator has modified 9 out of its fleet of 30 aircraft.

Manufacturers advice

The manufacturer advised that the overhead panel reverser fault light has only one purpose: to inform the crew that the reverser may deploy if another fault develops. No immediate action by the flight crew is required. The manufacturer recommends that the flight should continue to its destination.

The manufacturer is currently assessing whether, with the independent method of locking the stowed thrust reverser installed, it is possible to suppress the reverser light in flight.

During the return leg of a standard joy flight at 500ft, an Osprey struck and penetrated the left windscreen. The front seat passenger was slightly injured by impact and suffered cuts from Perspex shards. Control of the helicopter was not affected, and the pilot was able to land safely.

During short final approach to land at the completion of a local scenic flight, the aircraft encountered excessive sink and a sudden increase in crosswind. As a result, the aircraft bounced heavily on the runway threshold. The pilot then elected to go around and immediately applied full power.

During the climb out he noticed that the wings appeared to be damaged inboard of the tip tanks. Both tanks were full at the time. A decision was then taken to divert to Archerfield where the runway direction would better suit the prevailing wind. An uneventful landing followed.

Post flight examination of the aircraft confirmed significant damage to both wings.

FACTUAL INFORMATION

An instrument flight rules (IFR) flight plan had been submitted for a training flight in a Cessna 172 aircraft departing from Kempsey to Port Macquarie and various other points before returning to Kempsey. The flight was a navigation exercise with a student pilot accompanied by an instructor. The flight plan had been received by the relevant flight information centre. The student pilot broadcast a taxi call on very high frequency (VHF) radio while on the ground at Kempsey,, but he did not receive a response from flight service. The taxi call was in accordance with radio transmissions required for IFR flights and the pilot included the term "IFR" in his transmission. The Cessna was not fitted with a high frequency (HF) radio and the pilot continued the flight using the VHF radio. The Cessna became airborne at Kempsey without the pilot nominating an estimated time of departure for search and rescue ("ETD for SAR") with flight service. The first contact with flight service was after becoming airborne at Kempsey. The pilot then reported departure but did not advise the flight service officer that the flight was operating under the IFR category.

The flight plan had been processed in the flight service centre and a strip posted in the suspense bay on the console applicable to the Kempsey region. However, the flight service officer did not notice the flight strip and assumed the Cessna was a visual flight rules (VFR) category flight because the pilot did not notify the flight as IFR when he reported airborne at Kempsey. Consequently, the officer did not provide traffic information or activate the strip which remained in the suspense bay. During the period between the time the pilot of the Cessna 172 reported airborne and the time he reported his departure from Kempsey, the flight service officer handed over duties to a new officer. The new officer acknowledged the departure report and advised the pilot the area QNH. As there was no strip in the active bay, and the fact that the previous officer had not briefed her on the Cessna during the handover, the new officer also assumed the flight was VFR category. The new officer did not observe the flight progress strip for the Cessna in the suspense bay and did not provide traffic information.

At the same time, a DeHavilland Dash 8 aircraft conducting a regular public transport flight (RPT) from Sydney, inbound to Port Macquarie on descent, reported on the flight information area frequency. The crew of the Dash 8 received traffic information on two other IFR flights in the area but not on the Cessna. Nor did the pilot of the Cessna receive traffic information on the Dash 8 or any other IFR aircraft. The crew of the Dash 8, after making an inbound broadcast on the Port Macquarie mandatory broadcast zone (MBZ) frequency, established communications with the Cessna pilot. During the exchange of position information, the crew of the Dash 8 ascertained that the Cessna was IFR category. The Dash 8 crew then queried the flight service officer regarding traffic information on the Cessna and the officer replied that she was unaware of the Cessna. The flight service officer then contacted the pilot of the Cessna on the area frequency, obtained flight details and provided traffic information to, and about, other IFR aircraft. The pilot of the Cessna observed the Dash 8 as that aircraft descended for landing at Port Macquarie. The Cessna did not conflict with the Dash 8 or other IFR- category aircraft. The flight service officer later found the flight strip for the Cessna amongst other strips in the suspense bay.

ANALYSIS

The Aeronautical Information Publication (AIP) OPS NCTL - 3 para. 47.1 states that an "IFR aircraft operating from non-controlled aerodromes must report to ATS before taxiing. If unable to establish contact, proceed in accordance with para. 45.1." Paragraph 45.1 of the AIP indicates that if an aircraft is unable to contact air traffic services on VHF or HF while taxiing, the flight may proceed on a broadcast basis provided:

1. contact is established as soon as possible after take-off, and
2. for non-RPT flights, an estimated time of departure for search and rescue (ETD for SAR) has been established with a maximum of 30 minutes from ETD.

In this incident the pilot of the Cessna was unable to establish communications with flight service but continued the flight on a broadcast basis without establishing an ETD for SAR. The act of nominating an ETD for SAR may possibly have alerted the flight service officer to the fact that the flight was IFR. Also, the incident may not have occurred if the pilot had reported the IFR category of the flight to the flight service officer on first contact, or during the departure report. If the report had been made, the flight service officer would have been alerted that the flight was IFR category and would have provided the appropriate traffic and SAR alerting service. This would have probably been the situation whether the officer observed and used the flight strip or not.

While both flight service officers should have been alerted to the flight by the presence of the flight strip, the lack of IFR category notification in the transmissions from the pilot of the Cessna predisposed both officers to believe the flight was VFR category. Consequently, they did not re-check the suspense bay for a flight strip nor seek confirmation from the pilot. The instructor in the Cessna was aware that the flight service officer had not provided information appropriate for an IFR flight but did not query the officer. Confirmation by the instructor or the pilot of the IFR category of the flight would have ensured that the appropriate service was provided.

Both flight service officers displayed poor work technique on the handover/takeover, which was inadequate. They did not review all the information that was available to them on the console. Had either officer checked the suspense bay on an opportunity basis they may have observed the strip and recognised the flight was IFR category.

The Cessna pilot's adherence to MBZ procedures in broadcasting position information when approaching Port Macquarie was an active defence in the incident and served to break the chain of events. The pilots of the Cessna and the Dash 8 were able to ensure their own immediate separation by providing position reports using the MBZ frequency and to subsequently establish the Cessna's category with flight service. Ultimately, this enabled all IFR aircraft in the area to receive the necessary traffic information and for the Cessna to be provided with a traffic and SAR alerting service.

SIGNIFICANT FACTORS

1. The pilot of the Cessna 172 did not report "IFR" on first contact with flight service.
2. Neither flight service officer adequately scanned the console during the handover/takeover procedure.

SAFETY ACTION

Local safety action

As a result of this incident and other recent minor occurrences, the Manager Flight Service Sydney has:

1. reviewed handover/takeover procedures; and
2. formed a post-incident review committee to vet incidents for deficiencies and to recommend measures to minimise recurrences.

Bureau of Air Safety Investigation safety action

The Bureau of Air Safety Investigation issued interim recommendation IR960096 to Airservices Australia on the 5 November 1996:

"The Bureau of Air Safety Investigation recommends Airservices Australia amend the Aeronautical Information Publication to clarify the requirement for IFR category flights to report "IFR" on first contact with ATS when operating from non-controlled aerodromes."

The pilot of VH-CVG contacted Darwin Approach for an Airways Clearance, but due to other traffic in the CTA the clearance was not issued at that time.

A short time later the pilot again contacted approach for a clearance, and the aircraft was then identified at 5,500 ft within the CTA causing a procedural breakdown in separation with the other aircraft. The pilot was not aware that he had entered the CTA steps.

FACTUAL INFORMATION

A formation of four Skyhawk A4 aircraft had been flight planned to depart from Nowra on a low-level jet route flight over central New South Wales and then return to Nowra. The flight was notified in accordance with the Manual of Air Traffic Services (MATS) procedures and included a Notice To Airmen (NOTAM) which had been issued the day prior to the flight. The initial track of the flight was from Nowra, direct to Cowra at flight level (FL) 220, after which the formation would descend to low level, outside controlled airspace. The initial segment of the flight was to be conducted in controlled airspace which was the responsibility of a Melbourne based sector controller. The Melbourne sector controller was required to coordinate the flight with Sydney arrivals and another Melbourne sector.

The formation was to be intercepted by another Skyhawk immediately after departure from Nowra. The intention was for this Skyhawk to depart prior to the formation and to hold overhead Nowra. The pilot of this fifth aircraft would then intercept the formation as it departed Nowra. The intercept was planned to be completed by the time the formation reached a point 20 NM north-west of Nowra. This was just inside the area of responsibility of the Melbourne sector controller. The limit of Nowra military controlled airspace, on the planned track, was 15 NM northwest of Nowra. After the intercept, the fifth Skyhawk would continue on the same route planned for the formation.

Notification of the flight of the fifth Skyhawk was included as a note on the flight plan for the formation. The note advised that an aircraft with a callsign "TBA" (to be advised), would operate within 20 NM of the formation and would conduct an intercept of the formation. The flight plan did not state that there would be five Skyhawks or that the intercept would be conducted in the area between Nowra and 20 NM to the north-west. One hour prior to the Skyhawks' departure, Nowra air traffic control (ATC) contacted Melbourne ATC and co-ordinated the expected use of a block level of airspace from FL180 to FL250 for all five Skyhawks during the intercept. The actual levels requested would be co-ordinated when the aircraft taxied.

This was the first time the Melbourne sector controller had experienced an intercept situation and the degree of co-ordination necessary was significantly different to that which he had previously conducted for flights from Nowra. Another controller offered to assist the sector controller, but the offer was declined. The fifth Skyhawk taxied first and was cleared in accordance with the flight plan at FL220. The Melbourne sector controller co-ordinated this clearance with Sydney arrivals.

When the fifth Skyhawk was ready to depart Nowra, ATC co-ordinated the use of a block level. The block level requested was from FL180 to FL250. Nowra ATC advised that the pilot would remain on Nowra's frequency until the intercept was completed. The Melbourne sector controller requested confirmation of the extent of the area required for the intercept and was advised by Nowra ATC that the Skyhawk may require operations between 20 NM and 30 NM from Nowra. The Melbourne sector controller concurred with the use of the block levels. The sector controller did not issue a clearance limit for the aircraft or co-ordinate the use of the block levels with Sydney arrivals.

The Skyhawk formation taxied shortly after and was cleared via the flight planned route at FL220. The Melbourne sector controller co-ordinated the clearance with Sydney arrivals. The fifth Skyhawk became airborne at Nowra and climbed overhead the airfield. Nowra ATC passed radar identification on the fifth Skyhawk to the Melbourne sector controller. Prior to the formation departing, the Melbourne sector controller twice queried Nowra ATC with respect to the actual levels to be used by the two elements of Skyhawks. On both occasions Nowra ATC confirmed that both the formation and the fifth Skyhawk would be operating in the block level from FL180 to FL250 during the intercept.

The Melbourne sector controller advised both the Sydney arrivals controller and the other sector controller that the aircraft would be conducting an intercept and operating in the block level in his sector before transferring to their sectors. The two other controllers requested confirmation that all the Skyhawks would be maintaining FL220 on entering their airspace. The Melbourne sector controller confirmed that the Skyhawks would be at FL220.

The formation of Skyhawks departed Nowra and was transferred from Nowra ATC to the Melbourne sector controller 10 NM north-west of Nowra. The fifth Skyhawk was 8 NM behind the formation and Nowra ATC requested approval to maintain the aircraft on their frequency as the pilot was taking longer than expected to intercept the formation. This was not in accordance with radar control procedures in MATS which require all aircraft being radar separated to be operating on the same frequency. The Melbourne sector controller approved the fifth Skyhawk to remain on Nowra's ATC frequency after confirming that the aircraft was on descent to FL220. Shortly after, the fifth Skyhawk entered the Melbourne sector controller's area of responsibility but remained on a Nowra ATC frequency.

The Melbourne sector controller passed the radar identification of the fifth Skyhawk to the Sydney arrivals controller and advised that the aircraft was on descent to FL220. The Sydney arrivals controller accepted control of the fifth Skyhawk at FL220 and indicated that he was concerned because of a northbound B737 at FL230 that would be crossing the track of the Skyhawks. Traffic information on the B737 was passed to both elements of Skyhawks by the Melbourne sector controller and Nowra ATC. At no stage was the clearance for either Skyhawk element amended to restrict operations, in the block level, to a level that would ensure vertical separation from the B737.

The Skyhawk formation leader sighted the B737, and the pilot of the fifth Skyhawk advised Nowra ATC that he would not climb above FL220. Nowra ATC advised the Melbourne sector controller that the aircraft would not be above FL220. All five Skyhawks then transferred to the Sydney arrivals frequency. The Skyhawks were approximately 50 NM north-west of Nowra.

The pilot of the fifth Skyhawk reported to the Sydney arrivals controller that he was maintaining FL190. This was not the level that had not been co-ordinated by the Melbourne sector controller. The Sydney controller had based vertical separation with other aircraft in his sector on the previously co-ordinated level, FL220. The Sydney arrivals controller instructed the pilot of the fifth Skyhawk to descend to FL180 due to a Saab 340 at FL190. The pilot of the Skyhawk requested FL220 and was subsequently instructed to climb to FL220 by the Sydney arrivals controller. There was no breakdown in separation but there was breakdown in procedures.

ANALYSIS

More specific explanation of the special requirements for the formation flight would have assisted the sector controller to better appreciate the potential separation and co-ordination problems with the flight. This lack of information and the sector controller's lack of experience with this type of operation did not assist in his management of the task. The sector controller compounded the situation by declining the offer of assistance from another controller. This was a further sign of his inexperience.

The expectation by Nowra ATC and the Melbourne sector controller was that the intercept would be completed prior to the Skyhawks leaving the sector controller's area of responsibility. Because of this expectation, the sector controller did not co-ordinate the use of the block levels with Sydney arrivals or the other sector controller. Consequently, as a result of the intercept not being completed at 20 NM from Nowra, the Skyhawk continuing the intercept while remaining on the Nowra ATC frequency and the controller's own co-ordination workload, he was unable to appreciate the developing situation or eventual consequences.

The operation of the two elements of Skyhawks on different frequencies compounded the situation and caused a delay when the Melbourne sector controller attempted to confirm the aircraft were vertically separated from the B737. Retention of all aircraft operating within the particular block of airspace on a single frequency would have provided an improved level of safety for all the aircraft involved.

The lack of specific limits on the airspace to be used for the intercept pre-disposed the controller to losing control of the situation. Despite his obvious apprehension with respect to what was actually planned to occur, he did not impose any limits on the activity. The use of a suitable separation assurance technique or the co-ordination of the use of the block levels with subsequent sector controllers would probably have prevented the occurrence.

SIGNIFICANT FACTORS

1. The Melbourne sector controller lacked experience of this type of operation.
2. There were limited details of the special requirements for the military flight on the flight plan.
3. The sector controller did not co-ordinate the use of block levels with subsequent control agencies.
4. Aircraft did not operate on the appropriate air traffic control frequency.
5. Adequate separation assurance techniques were not used.

SAFETY ACTION

Local Safety Action

The commanding officer of the Skyhawk squadron agreed to issue two flight plans for similar flights in the future and to ensure that more explicit details of the military requirements are provided on the plans.

Two foreign military F18 aircraft entered the Darwin CTA without prior warning, or an airways clearance, 57 km south of Darwin and were observed on radar climbing to 9,000 ft.

A Beech Baron aircraft, in the exact same locality, had just been cleared to descend from 8,500 ft to 3,000 ft. A breakdown in separation occurred as the aircraft passed.

The aircrews of the foreign aircraft were rebriefed on Australian ATC procedures and requirements.

The pilot was operating a helicopter joy flight from Coolangatta to Cook Island and return. On board were the pilot and four passengers. The pilot reported that the helicopter's engine failed while flying about 50 metres offshore, at a height of approximately 500 ft. He said that at the same time he noticed the power loss, the engine-out light started flashing. During the subsequent forced landing, the helicopter landed heavily, coming to rest upright, but slightly nose down in about 30 cm of water. During the landing the main rotor blades flexed downwards and severed the tail boom.

After the helicopter came to rest the pilot assisted the passengers to safely exit the aircraft.

The pilot advised that the engine continued to run at a very low idle for some time before he re-entered the helicopter and closed the fuel shut-off control.

Based on information provided by the pilot the helicopter's weight and balance were assessed to be within limits.

The investigation revealed that the nut which secures the bleed air sensing line between the power turbine governor and the fuel control unit was loose at the fuel control end. The loss of this sensing function limited the available fuel flow. As a result, engine rpm reduced uncontrollably to a low idle.

Fret marks on the mating surfaces of the nut and the male nipple at the rear of the fuel control indicated that the engine may have operated for a period of time with the nut loose. Specialist metallurgical examination was unable to determine how long the nut had been loose. After the accident, a substitute sensing line was fitted and the engine operated normally. Examination of the maintenance documentation could find no evidence of any recent work being carried out on the sensing line.

FACTUAL INFORMATION

Two international B767 aircraft were tracking northbound on air route B220 at Flight Level (FL) 350, the second approximately 20 minutes behind. All separation in regard to these two aircraft was correctly established and maintained. The aircraft were under the control of Brisbane Sector 10 and were due to cross into the Papua New Guinea flight information region (FIR) at VIPAM, the mandatory reporting position at the FIR boundary. The controller had co-ordinated the pilot estimates for VIPAM with Port Moresby Control.

Subsequently, an A310 aircraft taxied at Port Moresby for a flight to Cairns via air route B220 and the crew had been cleared to climb to FL370 by Port Moresby Control. The Sector 10 controller agreed to this flight level as initial separation responsibility was with Port Moresby Control.

The A310 departed at 1316 EST and was estimating VIPAM at 1341 tracking southbound. As the first B767 was estimating VIPAM northbound at 1346, there was insufficient time to allow an unrestricted climb to FL370 for the A310. The crew were therefore instructed by Port Moresby control to maintain FL330.

During the subsequent co-ordination between Port Moresby control and Sector 10, it was agreed that Sector 10 would accept responsibility for providing separation between all three aircraft and initiating a climb for the A310 when available. During this co-ordination the Port Moresby controller offered the use of Port Moresby distance measuring equipment (DME) to assist Sector 10 in this separation function. The Sector 10 controller was unsure of the process for using such equipment in Australian airspace and decided not to use the DME standard.

Having accepted responsibility for separation, the Sector 10 controller correctly calculated, using mental processes only, a time of passing for the A310 and the leading B767. The estimated time of passing was 1343.30 (transmitted to the aircrews as 1343) and the aircraft sighted each other at that time. However, further climb for the A310 was still dependent on separation being provided with the second B767, which was initially estimating VIPAM at 1416.

While the Sector 10 controller was waiting for confirmation that the first B767 had passed the A310, she commenced the calculation for the time of passing for the A310 with the second B767. The controller's mental calculation was based on a 27-minute time difference derived from the revised VIPAM estimates of the A310 (1341) and the second B767 (1408). The controller calculated this time of passing as 1404 (this was erroneous as the correct time was 1353.30). The required standard was for the climbing aircraft (A310) to reach FL370 by a time 10 minutes before the time of passing. Based on the controller's calculated time of 1404, this requirement would have been 1354. However, because half-minutes are not normally used in these calculations, the controller rounded out on the side of safety and issued an instruction for the crew of the A310 to climb to FL370 with a requirement to reach FL370 by 1353.

At 1347, the crew of the B767 reported their position at DOTOD (a position on air route B220 south of the FIR boundary) and gave an updated estimate for VIPAM that was 2 minutes early. This new estimate had the effect of bringing the time of passing forward by 1 minute and the Sector 10 controller issued a new requirement for the crew of the A310 to reach FL370 by 1352. This requirement was correctly acknowledged.

At 1348, the crew of the A310 reported maintaining FL370. The aircraft passed at 1353. The Sector 10 controller had made a 10-minute error in the time of passing calculation and the separation standard had been breached.

Communication with the three aircraft in the relevant portion of air route B220 was through flight service HF channels. All transmissions and co-ordination procedures in regard to flight service requirements were adequate and in accordance with the appropriate instructions.

The Australian Manual of Air Traffic Services suggests that where separation is based on mathematical calculation, a cross-check of the results should be undertaken. On this occasion, the controller had intended to make such a cross-check using a navigation computer and had prepared the flight progress strip for the northbound B767 in readiness to carry out the second calculation. However, no such check was made. She had only checked her original calculation using the same mental method.

The workload on the Sector 10 controller had been high but most of the traffic separation conflictions had been completed, with co-ordination representing the bulk of the outstanding tasks at the time of the occurrence. However, the sector was still considered to be busier than normal.

ANALYSIS

Examination of the time of passing calculation indicated that using the 27-minute difference and the time of 1341 at VIPAM for the A310 (the point at which the controller based her separation calculation), the calculation should have resulted in a time of passing of 1354.30. This time would have then been rounded out to 1354 and then further amended to 1353 when the crew of the A310 reported at VIPAM at 1339. The difference of 1 minute in this time of passing calculation as compared to the controller's calculation (after subtracting the 10 minutes required by the separation standard and correcting the controller's 10-minute error), could not be adequately explained but was probably a safety net used by the controller when a half-minute was involved in the calculation. Having made the original 10-minute error, the controller made amendments in the single minute column and, because a cross-check was not carried out, the opportunity to remedy the mistake was lost.

The Sector 10 controller knew that a cross-check was required and had intended to carry out such a check for the time of passing involving the second B767. She could not say why this was not done but she was busy and had several items on her mind at the time. One such item was the option to use Port Moresby DME to establish a definite passing. She was unsure of being able to use a foreign navigation aid in Australian airspace and was discussing this option with other controllers.

Having made an error of 10 minutes in the time of passing calculation, certain factors may have reinforced the controller's perception that all was well. Firstly, the time of passing for the A310 and the first B767 had been correctly calculated and had worked as planned. Secondly, the initial estimated times at VIPAM between the A310 and the second B767, indicated that there was enough time for the change of level while maintaining separation standards provided that the crews of the A310 and the preceding B767 saw each other, and that the instruction for the climb was given as soon as those sighting reports were made. This situation would have provided 10 minutes for the crew of the A310 to complete their climb.

Additionally, the controller wanted to provide a good service and give the crew of the A310 the least possible delay for their climb.

However, irrespective of the times involving the A310, there was only a period of 20 minutes between the two northbound aircraft. This period was insufficient for the crew of the A310 to obtain a sighting and positive passing of the first B767, and then to climb to reach FL370 at least 10 minutes prior to passing the second B767.

The position reports that were subsequently made by the three crews indicated that all aircraft reached VIPAM earlier than initial estimates. This situation reduced the time available for the A310 to safely climb when using the controller's incorrect calculations. The aircraft actually passed at 1353.30.

SIGNIFICANT FACTOR

The Sector 10 controller did not carry out a cross-check of the time of passing as suggested by the Australian Manual of Air Traffic Services.

SAFETY ACTION

As a result of the investigation, Airservices Australia issued an instruction to draw the attention of controllers to the common error of carrying the "one" in any 10-minute calculation. They also introduced an additional tool for controller reference in the form of a Time of Passing Graph.

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