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

Vertical separation diminished to about 500 feet between two aircraft in controlled airspace. VH-STC was on climb from Essendon, and VH-TWC was ex Geelong and cruising at 6,000 feet.

Initially VH-STJ was cleared to climb to 6,000 feet, but when the departures controller realised that VH-STJ's groundspeed was too slow for it to remain ahead of VH-TWC, he cleared VH-STJ on climb to 5,000 feet and wrote the amended altitude on VH-STJ's flight strip.

To resolve potential conflict with other traffic in the Melbourne area, both VH-STJ and VH-TWC were issued with an amended route clearance, Melbourne - Fenton's Hill - Mangalore. When issuing this amended route clearance, the controller followed the normal practice of including the cleared level. However, he inadvertently cleared VH-STJ to the original flight planned altitude of 6,000 feet instead of the amended altitude of 5,000.

When the controller noticed by radar that VH-STJ continued to climb through 5,000 feet he queried the pilot who discontinued the climb.

Significant Factor

The following factor was considered relevant to the development of the incident:

1. The air traffic controller inadvertently cleared VH-STJ to the wrong altitude.

It was reported that planned mustering and other activities had been significantly delayed by poor weather and there was pressure to complete the task. The pilot did not sleep well on the night prior to the accident because of his concern about progress.

On the day of the accident the station strip was assessed as unsuitable for aircraft operations due to its soft surface. As a last resort, arrangements were made to fly the aircraft from an access road. A straight section of the road, 350 m long, was selected. There was a cattle grid, with guideposts, at the end of the section. The pilot estimated there was sufficient distance available to become safely airborne.

During the take-off the pilot experienced control difficulties caused by vehicle ruts in the road surface. The aircraft veered to the left and the left main wheel entered a soft area. The aircraft's acceleration was retarded but, as there was insufficient room to stop safely, the pilot continued with the take-off. Immediately after lift-off there was a loud bang. The pilot thought the tail wheel had struck one of the guideposts. Although the aircraft appeared to be operating normally, he elected to complete an immediate landing on a serviceable airstrip about a kilometre away. During the landing roll the left main landing gear collapsed as a result of damage caused by the collision with the post.

During the take-off run, just before reaching V1, the crew heard two bangs in quick succession. Both the No 3 engine EPR and EGT indications were seen to fluctuate, so the take-off was immediately rejected. Whilst decelerating, the crew requested a frequency to communicate directly with the Rescue and Fire Fighting Service (RFFS) but were given the ground control frequency. That frequency was cluttered with other traffic, which made direct communication to RFFS difficult. They were finally referred to a different frequency. The aircraft vacated the runway onto taxiway Alpha 5 where a small brake fire was extinguished by the RFFS. The aircraft was subsequently towed back to the departure gate, where the passengers and crew disembarked.

Ground inspection revealed damage to several compressor stages of No.3 engine. The engine was changed, and the aircraft released for service.

Safety Action

The Bureau of Air Safety Investigation is evaluating aspects of a discrete air traffic services frequency on which aircrews and rescue firefighting services at airports can be transferred during an emergency situation. Any forthcoming recommendations will be published in the Quarterly Safety Deficiency Report.

FACTUAL INFORMATION

Sequence of events

The flight was to conduct photographic work around the Kununurra area. The crew consisted of the pilot in command and a second pilot in the right front seat to assist with look-out, radio communications and communicating with the photographer. The photographer operated from the rear seat without a headset.

After the crew had completed part of the task, the pilot started to climb the aircraft to a higher altitude. As the aircraft passed about 600 ft above ground level, the engine stopped suddenly without warning. The pilot transmitted a Mayday message and carried out a forced landing into 30-foot trees. During the impact, the aircraft turned over and the stitching of the harness of both pilots came undone, releasing the shoulder harnesses.

The pilot in command and the photographer suffered minor injuries. The right-seat pilot was seriously injured.

Wreckage

The aircraft came to rest inverted with the left wing torn off. The propeller blades were broken but showed no signs of rotation during impact. The Bureau was advised that, four days after the accident, an inspection of the fuel tanks indicated that the right tank was about three-quarters full, while the left tank contained only about 20 litres. Fuel was leaking from the impact-damaged left tank-to-engine feed lines. Consequently, the fuel quantity remaining in the aircraft at the time of the engine failure could not be accurately determined. Subsequent specialist inspection of the fuel-system components found that the engine-driven fuel pump outlet port was blocked by grit wrapped in fibrous material. The system filters were also contaminated.

The aircraft was normally refuelled at Kununurra, but had been refuelled from drums when operating from another strip in the area.

Aircraft maintenance

Further inspection of the engine found that the mixture control was excessively worn and that three spark plugs could be unscrewed by hand. The time at which contamination of the fuel system occurred was determined. The last periodic inspection was conducted 94 hours prior to the accident.

Emergency locator transmitter

A portable Pointer 3000 emergency locator transmitter (ELT) was carried in the baggage compartment. The ELT was turned on by the pilot after the accident and its signal was detected by the Brisbane Search and Rescue Co-ordination Centre.

ANALYSIS

The reported blockage of the engine-driven fuel pump outlet port is consistent with the circumstances of the engine failure. Contamination could have been introduced to the system if appropriate filtration was not used during refuelling from drums. Although there were indications that the aircraft maintenance was deficient, there was insufficient evidence to suggest that inadequate maintenance was implicated in the circumstances of the accident.

SIGNIFICANT FACTOR

It is likely that engine power was lost due to fuel starvation caused by system contamination.

The pilot was tracking for left base, runway 22 (about 290 degrees), and was instructed to report abeam the Queen Elizabeth 2 stadium. A twin- engined aircraft, VH-DRB, was descending to 1500 feet from CTA to the south east of Archerfield. The pilot of this aircraft had initially requested a landing on runway 28 but the controller had difficulty in facilitating this request. The controller ultimately instructed VH-DRB to make a visual approach via a wide left base for runway 22, and to follow a third aircraft on final approach.

In VH-JVV, the pilots were monitoring the progress of VH-DRB by radio. The trainee instructor alerted the pilot in command to the position of the other aircraft. An immediate climbing turn was initiated in order to avoid a collision. The controller attempted to confirm that JVV had VH-DRB in sight at about the same time.

The pilot of VH-DRB saw the other aircraft during its avoiding turn. His aircraft was still descending, and the other aircraft was probably hidden from view by his aircrafts nose section, the instrument combing or the right windscreen pillar. He did not take any avoiding action.

The aerodrome controller had not passed traffic information about each other to the two aircraft involved. The warning transmission from the controller was made at the same time as the pilot of VH-JVV reported at QE 2 stadium.

The pilot of VH-DRB originally requested runway 28, and the controller had initially attempted to facilitate this request. In doing so he had not considered the possible track of that aircraft when it was instructed to track for a wide left base for runway 22.

The weather at the time was fine, with a clear sky and unrestricted visibility.

At 1025 the pilot of VH-NJY contacted Mackay Tower at 30 NM inbound on the 155-degree radial on descent to 6,000 ft. VH-NJY was then cleared to descend to 4,600ft and track via a 5 NM arc to the west of track and then to track overhead for a NDB approach. At 1027, VH-EWS departed Mackay for Brisbane tracking on the 137-degree radial on climb to 10,000 ft. Mackay tower controllers commenced trying to visually observe VH-NJY inbound. This was done by the use of standard issue binoculars. The inbound track of the aircraft is situated over a prominent topographical feature known by tower staff, however, VH-NJY could not be visually acquired at this stage. At 1029, VH-NJY was observed visually at approximately 12 NM and 12-13 degrees east of track. VH-EWS was 6 NM on the 137-degree radial. VH-NJY was instructed to turn left to commence the diversion for the NDB approach.

A traffic alert was not issued to the aircraft, as it was the judgement of both controllers on duty that although the aircraft were found to be closer than normal, a collision risk did not exist. They believed there was approximately a mile laterally between both aircraft, and they were diverging. Subsequent replay of the radar tape indicated that VH-NJY and VH-EWS passed each other within approximately 0.7 NM laterally and 800 ft vertically. The Aeronautical Information Publication Australia (AIP) Air Traffic Rules and Services (RAC) 44.4.3 requires aircraft to be navigated by reference to the aid which provides the most precise track guidance, which in Mackay is the Mackay VHF Omni Range (VOR). The pilot in command is required at all times to take positive action to regain track as soon as a deviation from the correct track is recognised. The VOR tracking tolerance at 10 NM is approximately plus or minus 0.9 NM VH-NJY indicated on radar as being approximately 2.6 NM off track at 10 NM which is 1.7 NM outside the approved tolerances. Had this fact been known to air traffic controllers, then corrective action to ensure separation could have been taken. Mackay tower is not equipped with radar. Radar data from Swampy Ridge radar sensor is processed through the technical facilities at Mackay, enroute to Brisbane centre, but no radar display is provided for tower controllers. VH-NJY was under radar control during the flight until the aircraft was transferred to Mackay tower at 30 NM when radar services were terminated. The separation technique being used by tower controllers was one of visually monitoring the outbound aircraft on a track that was plotted on a map to be clear of the procedural tolerance, (in this case 5.2 degrees off the VOR radial, plus an additional 1 NM lateral separation buffer), of the inbound aircraft. No documentary evidence could be found to permit the application of this standard.

The pilot in command (PIC) of VH-NJY was a check captain and the copilot (CP), a first officer, was undergoing command training. The PIC had requested an NDB approach as a training exercise and had selected the VOR selectors off to simulate their failure. He was aware of VH-EWS departing on the 137 radial and tracking to Gladstone. At 10 NM he noted that the trainee had allowed the aircraft to diverge to the right of the 155 radial. The PIC did not bring this to the attention of the trainee, in order to see if he was going to fly outside tracking tolerances. The PIC said that at no time did the ADF needles indicate the aircraft was any further east than the 150 radial. He was satisfied that the aircraft was well clear of the Hay Point helicopter pad which is located near the 137 radial. He also had VH-EWS in sight passing to the right and was satisfied he was well clear. In summary, the PIC of VH-NJY was operating outside tracking tolerances and outside the terms of his airways clearance. This was due to deselection of the most accurate navigation aid (the Mackay VOR) to simulate its failure for training purposes. A non documented separation standard was used by the tower controllers. An instruction has been issued to all Northern District Towers that until a separation standard is developed and approved, outstation staff are to apply only those separation standards that are included in the Manual of Air Traffic Services (MATS).

The radar sector providing enroute control to VH-NJY did not advise the pilot that radar services were terminated when he was handed off to Mackay tower. The District Safety and Quality Management Branch has recommended that radar controllers advise pilots proceeding into procedural tower environments within radar coverage, when radar services are terminated. Weather conditions were fine, with Mackay under the influence of a high-pressure system, QNH 1023, nil cloud, visibility in excess of 10 km, and a light south-easterly wind.

The pilot reported that he lowered the gear on the downwind leg of the circuit and the green light illuminated, indicating the gear was fully down and locked. The remainder of the landing checks were completed before turning base. A gentle touchdown on the main gear was made on the threshold of runway 15. As the nosewheel was lowered onto the runway, the operating lever came out of the lock and the gear retracted.