1. FACTUAL INFORMATION

1.1 Sequence of events

The aircraft was on a powerline inspection flight. It was crewed by a pilot employed by the operator of the aircraft and by an observer from the power supply company. The purpose of the flight was to enable the observer to identify obstructions in the form of trees and branches potentially too close to the powerlines and constituting a fire hazard, and to assess the condition of the conductor and associated items.

To enable the observer to inspect a powerline such aircraft are flown 150 feet above ground level, at 70 knots, with flaps extended 10 degrees. The aircraft is tracked down the left side of the powerline to give the observer in the right seat a good view of the line.

Shortly before the aircraft crashed, it was observed flying along a spurline. It was at this time flying essentially downwind. Some minutes later, the wife of a nearby farmer who had been listening to the approaching aircraft realised that she could no longer hear the engine. Her husband located the wrecked aircraft in a paddock and initiated an emergency response. There were no witnesses to the accident. Neither the pilot nor the observer survived the impact.

1.2 Wreckage and impact information

The aircraft had impacted the ground in a nose-down attitude of approximately 45 degrees. The right wing was down approximately 30 degrees relative to the horizon. The wreckage trail was short, indicative of low forward speed at impact. The disposition of the wreckage indicated that the aircraft had been rotating to the right before impact.

Wreckage analysis disclosed no pre-impact faults. The aircraft had sufficient fuel for the flight and had been properly maintained. There were no pre-existing defects recorded on the maintenance release. The pilot had updated personal, company and aircraft records at the completion of the previous day's flying.

1.3 Pilot details

The pilot commenced flying training in 1987. He obtained his commercial pilot licence in December 1991, an instructor rating in May 1992, and a command instrument rating in July 1993. His logbook recorded that while flying as an instructor he had instructed student pilots on the causes of stalling and on stall recovery techniques. He had flown a total of 1,276 hours.

He commenced his training in powerline inspection flying techniques on 19 July 1994. After eight hours instruction over five flights, he was assessed as having met the required standard. Accordingly, he was approved to conduct powerline inspection flying for a period of 12 months. At the time of the accident, he had conducted 209 powerline inspection flights totalling 462 hours. The latest check for revalidation of his powerline inspection flying approval, carried out on 13 July 1995, was valid for one year and was therefore valid at the time of the accident.

The pilot had ferried the aircraft from Moorabbin to Hamilton three days prior to the accident. Including the ferry time, he had flown for four hours, two hours and three hours respectively, on the three days prior to the accident. On the day of the accident, he flew for just under three hours. The aircraft was one of two that were conducting powerline inspections out of Hamilton aerodrome. The pilot of the second aircraft advised that the crews had a quiet night and were well rested before commencing the day's operation.

The pilot held a valid medical certificate. The post-mortem examination did not disclose any medical factors that may have contributed to the accident.

1.4 Meteorological information

The property owner advised that the weather at the time of the accident was fine with a light breeze from the northwest. This was consistent with the forecast issued by the Bureau of Meteorology which had predicted a 15-knot breeze for the area. Weather was not considered to have been a factor in the accident.

1.5 Roll and cut manoeuvre

If an observer does not get a clear view of an obstruction, then the aircraft is required to fly a specific manoeuvre to give the observer a better view. The manoeuvre is called a 'roll and cut'. When the aircraft is flying on the left of the line and the observer calls 'roll' the pilot rolls the aircraft to the right to cross the powerline at 45 degrees. This enables the observer to look back down the line at the obstruction. If after crossing the line, the observer requires a further look at the obstruction, he calls 'cut'. The pilot then continues the right turn until the aircraft has turned through 270 degrees from the original heading. The aircraft is then rolled wings-level to cross the line at right angles, giving the observer a clear view of the obstruction to the right as the aircraft passes over the line. After crossing the line, a 270-degree left turn is made to re-position the aircraft to continue the inspection.

The wreckage was located in a paddock with the wreckage trail aligned nearly at right angles to and under the powerline that was being inspected. In the paddock there was one line of scrub before the accident site and one tree after the accident site that might have been subject to a cut and roll inspection manoeuvre. Due to the lack of witnesses to the accident the investigation was unable to determine what manoeuvre was being carried out prior to the loss of control which preceded the accident.

The power supply company advised that in the year before the accident, some 56,000 km of line was patrolled, finding 27,514 trees that needed attention. This would mean that to verify the hazard, at the very least one cut and roll is required for approximately every two kilometres flown.

1.6 Powerline inspection: flight parameters

The aircraft operator and the power supply company determined the optimum height for inspection of powerlines to be 150 feet above ground level and the optimum speed to be 70 knots. It is the pilot’s responsibility to maintain these parameters. The height of the power poles varies between 25 feet and 40 feet. There was evidence that, on occasions, powerline inspection aircraft had been observed to fly lower than 150 feet. Some pilots had commented that occasionally the observers asked for the aircraft to be flown at a lower height. The pilots considered that this might have been due to difficulty observing powerlines in certain conditions of sun and light and to the difference in visual acuity between individual observers. The power supply company did not have standards for, and did not require a check of, the observer's visual acuity. When the observer completed his training two years before the accident his visual acuity was obviously acceptable. However, there was no ongoing program to check and detect any deterioration that may have occurred since that time.

1.7 In-flight incapacitation

Post-mortem examination disclosed that the observer suffered from asthma and had advanced heart degeneration.

Microscopic examination of his lungs showed changes in keeping with asthma. However, no macroscopic findings were seen that would have indicated he had suffered a severe asthma attack.

The post-mortem examination showed significant coronary artery disease with a 75 per cent stenosis of the left anterior descending coronary artery. Expert pathological opinion was that an individual with significant coronary artery disease may have an episode of myocardial ischemia leading to severe pain or change in conscious state. However, the physical reaction could be expected to be benign, resulting in slumping of the body. The observers sit with the seat at the limit of its aft travel to enable them to use their maps clear of interference with the control column and to give the best view through the right window. It is unlikely that control interference would occur due to a body slumping while the seat was in the aft position. It could not be determined if the observer suffered any form of incapacitation in the period immediately before the accident.

Neither the observer's family nor his employer was aware of his medical condition. The employer did not require the observers to meet a minimum medical standard.

1.8 Flight path simulation

A flight was undertaken to simulate the inspection of the spur line that was being inspected immediately prior to the accident. The flight was conducted by the operator's manager of powerline flying and conformed to the required parameters of height, speed, and configuration. The flight was watched by some persons who saw the accident flight, shortly before the accident, and by some who had watched other powerline inspection flights. They said that they had seen many flights, including the accident flight, operated either more slowly and/or at a lower height and/or with greater bank angles, than those demonstrated during the simulation flight.

2. ANALYSIS

The accident probably occurred when control of the aircraft was lost while it was flying at a height too low for the pilot to apply effective stall/spin recovery techniques. The sequence of events that led to the loss of control could not be established because there were no witnesses to the maneouvres that preceded the accident. However, there was evidence that some powerline inspection flights had not complied with the operator's height, speed, and angle of bank requirements. This may indicate that some of the pilots had become complacent and had a lowered awareness of the dangers of flying low and slow and lacked appreciation of the importance of strictly adhering to the operator's flight parameters.

Although the observer was suffering from a medical condition which may have led to his becoming disabled, there was no evidence that this had occurred. Had an episode occurred it could have resulted in severe pain or collapse. Either could well have been distracting to the pilot. It is unlikely that the onset would have been of such severity as to cause involuntary limb and body movements that may have interfered with the flight controls, leading to loss of control of the aircraft.

3. CONCLUSIONS

3.1 Findings

1. The aircraft was properly certificated and maintained, held sufficient fuel for the flight, and was serviceable at the start of the flight.
2. The pilot was properly licensed and had been properly trained and checked for conducting low-level powerline flights.
3. Some powerline inspection flights had been observed to deviate from the required flight parameters.
4. The power supply company did not have minimum medical standards for its observers.
5. The observer had a medical condition that may have incapacitated him.

3.2 Significant factor

1. Control of the aircraft was lost at a height from which the pilot was unable to recover.

4. SAFETY ACTION

4.1 Immediately after the accident the power supply company suspended flying and, with the operator, assisted in the conduct of the investigation. When it became apparent that the operator's flight parameters were not always being observed, the operator instituted a campaign to improve pilot awareness and discipline. When flying recommenced, the observers advised that there was a marked difference in the way the pilots manoeuvred the aircraft.

4.2 Both the powerline company and the aircraft operator conducted a major reassessment of the operation. They have decided to:

(a) fit four-piece crew restraint harnesses to all aircraft;

(b) supply crash helmets for both the pilots and observers, and require that they be worn;

(c) require observers to meet a minimum medical standard; and

(d) initiate crew resource management training for pilots and observers, with emphasis on safety awareness.

4.3 Before the accident the operator and power supply company commenced experimenting with the use of differential video imaging and infra-red detectors to aid in the identification of hazardous trees. When implemented, this system is expected to reduce the need for continuous roll and cut manoeuvres. The optimum height above ground level for this system has been determined to be approximately 250 feet which should improve the margin of safety.

1. FACTUAL INFORMATION

1.1 History of the flight

The pilot planned a private business flight under visual flight rules (VFR).  He took off from Moorabbin shortly after 0800 EST and collected two passengers from Melbourne Airport prior to flying to Warrnambool.   After working in the Warrnambool area during the day, he took off from runway 31 at about 1948 EST.  Conditions in the circuit area were very dark with limited ground lighting, high overcast cloud, some low cloud, and patches of drizzle.

The complete flight path after take-off is unknown.  However, witnesses heard and saw the aircraft flying low to the north-west and west not far from the aerodrome.  The last sighting was of the aircraft climbing to the east-south-east towards the centre of runway 31, followed by a left turn and a steep left spiral dive from an estimated height of about 500 feet.  At 1950 the aircraft crashed 255 metres to the right of runway 31 centreline. Runway 31/13 lights were illuminated at the time.

At impact the fuel cells burst.  There was a flash fire along the wreckage trail.  However, most of the fire damage was confined to the detached wings.

1.2 Damage to aircraft

The aircraft was destroyed by the ground impact and by post-impact fire.

1.3 Weight and balance

The aircraft weight and balance were within approved limits for the flight.

1.4 Personnel information

The 54 year old pilot was correctly qualified and endorsed to perform the flight.  He held a private pilot licence (aeroplanes) and a single-engine night rating valid for automatic direction-finding equipment and very high frequency omni-directional radio range.  The night rating was issued on 11 October 1994.  His total night flying experience was 22.3 hours.  This comprised 13.3 hours dual flight instruction in a Piper PA28, a 3.3 hours flight test in a PA28 with an approved testing officer, and 5.7 hours as pilot in command, of which 2.5 hours were in a PA28 and 3.2 were in the Cessna 182.  His most recent previous night flight occurred on 6 October 1995.  His Civil Aviation Safety Authority medical certificate was valid until 14 August 1997.  He was required to wear spectacles for close vision.

1.5 Meteorological information

A weather observation taken by a trained observer at Warrnambool at 1800 indicated: QNH 1011.6 hectopascals, surface wind 320 degrees 18 knots, visibility 20 kilometres, light rain, cloud 8 octas of altocumulus base at 8,500 feet, temperature 15 degrees Celsius, dew point 15 degrees Celsius.

An observation taken at Warrnambool at 2100 indicated: QNH 1015.5, surface wind 230/10 knots, visibility 50 kilometres, weather nil, cloud 8 octas of altocumulus, base 8,500 feet, temperature 13 degrees Celsius, dew point 15 degrees Celsius.

Charts provided by the Bureau of Meteorology indicate that the accident occurred as the tail end of a cold front was passing through Warrnambool.

Witness evidence of weather at the time of the accident varies.  However, the consensus was that it was very dark because cloud had obscured the moonlight, and that there was intermittent drizzle in the area. Because it was so dark, witness estimates of cloud amount and height varied but indicated that there were patches of cloud below 1,000 feet in the area.

At 1900, before leaving Warrnambool city, the pilot telephoned the Civil Aviation Authority briefing office, and a briefing officer gave him a detailed update on the forecast weather for the proposed flight.  The pilot had already submitted a night visual flight rules flight plan for the return flight to Moorabbin via Avalon.  During the five-minute discussion, the briefing officer advised of the area forecast 30/32, Melbourne aerodrome forecast, and Moorabbin aerodrome forecast.  From the discussion it was apparent that the pilot was fully aware of a weather front passing through Warrnambool at about the time of the telephone call.  He advised the briefing officer that there were some fairly low cloud layers at Warrnambool at the time.  The forecast weather ahead of the front and well behind it was suitable for night visual flying, whereas weather associated with the front included scattered cloud from 1,000 feet to 2,000 feet and visibility reduced to 3,000 metres in drizzle.  He advised the briefing officer that if he could depart Warrnambool quickly, he would be ahead of the trough and that he would telephone the briefing office again to lodge a search-and-rescue time when he was about to depart Warrnambool aerodrome.

The taxi driver who drove the pilot and the two passengers to the aerodrome, arriving at about 1930, advised that as they neared the aerodrome it was a moonlight night, but the clouds were rolling in from the west and starting to obscure the moonlight.

At 1933 the pilot telephoned the briefing office from the aerodrome and lodged a search-and-rescue time of 2130 for arrival at Moorabbin.  The briefing officer advised that Warrnambool was probably still east of the trough/cold front.

1.6 Aids to navigation

Warrnambool has a pilot-monitored non-directional beacon which was transmitting on 395 kilohertz at the time of the accident.

1.7 Communications

Warrnambool has a common traffic advisory frequency of 126.0 megahertz which is not recorded. The common traffic advisory frequency applies for a radius of five nautical miles and up to 3,000 feet above the aerodrome reference point.  Had the pilot flown beyond five nautical miles or above 3,000 feet, he probably would have made a departure call to Melbourne flight service and this call would have been recorded.  The flight service communications tape has since been monitored.  No departure call was recorded.

1.8 Aerodrome information

Warrnambool Airport is 11 kilometres north-west of Warrnambool city.  It has two runways.  Runway 31/13 is the only one with runway lighting installed.  The runway lighting is a pilot-activated system. Because the runway lights were on, it is probable that the pilot of VH-XTK had activated them prior to take-off. Runway 31/13 is 1,372 metres long, 30 metres wide, and the surface is asphalt.  The aerodrome is 242 feet above sea level.  The surrounding terrain varied from relatively flat to gently undulating.

1.9 Wreckage and impact information

The impact site was abeam a position approximately 925 metres along runway 31 and 255 metres to the right of centreline.  At impact the aircraft was an estimated 70 degrees nose down, facing 278 degrees magnetic and left wing low.  Wreckage was spread over 107 metres in the direction of 008 degrees.  The engine was torn out of the airframe and was found four metres from the point of initial impact.  Most of the fuselage came to rest within 58 metres of the initial impact point.  Both of the wings were torn off.

The control system was inspected and the damage sustained was consistent with impact damage. The flaps were up at impact.

The propeller was torn from the engine. A subsequent inspection showed evidence of its being within one degree of full fine pitch at impact.

The engine and its accessories were inspected.  A metallurgist examined the exhaust pipe and confirmed that the engine was producing hot exhaust gases at impact.

The engine-driven vacuum pump was subsequently determined to have been serviceable at impact.  The artificial horizon showed impact evidence of a steep nose-down attitude.  The turn co-ordinator showed evidence of hard left bank at impact.  The altimeter subscale setting was 1013 hectopascals.

Fuel filters were found clean.  The fuel on board was of the correct type and of sufficient quantity for the flight.

No fault was found with the aircraft or its systems that may have contributed to the accident.

The accident was not survivable.

1.10 Medical information

The specialist forensic pathologist who performed the autopsy on the pilot documented the cause of death as multiple injuries.  However, he advised that the presence of ischaemic heart disease in the pilot may have contributed to the accident.

1.11 Emergency locator beacon

The emergency locator beacon did not function correctly after the accident.  The antenna cable was severed at impact. When tested, a low-level signal was received at very close proximity.  The battery was one month past its replacement date, but the voltage was within tolerance.  The negative terminal was corroded, causing a high resistance joint which resulted in low signal strength.

1.12 Spiral dive

Some basic spiral dive trials were subsequently conducted in another Cessna 182R.  With his aircraft at 6,000 feet and trimmed to 100 knots indicated airspeed, 20 inches manifold air pressure and 2,400 revolutions per minute, the pilot closed the throttle and gently banked the aircraft 45 degrees left without applying back pressure on the control yoke to maintain height.  The nose began to drop.  By 100 feet height loss, the vertical speed indicator had reached 500 feet per minute rate of descent.  With 280 feet total height loss, the vertical rate of descent was 1,400 feet per minute. With 450 feet total height loss, the vertical speed indicator needle was on the 2,000 feet per minute descent stop and the indicated airspeed was 125 knots.

A similar exercise was conducted leaving the power at 20 inches manifold air pressure.  In about 200 feet height loss, the vertical rate of descent reached 2,000 feet per minute and the airspeed was about 135 knots and increasing rapidly.

1.13 Pilot training

The pilot's night VFR training was conducted from Moorabbin by a Grade Two instructor.  The training included navigational exercises to Essendon, Latrobe Valley, Bendigo, Ballarat and Mangalore.  In excess of three hours dual night circuit training was conducted at Moorabbin and Latrobe Valley.  The pilot also performed night landings and take-offs at Bendigo, Ballarat and Mangalore.  The Mangalore circuit area was known to contain minimal ground lighting.

The pilot's instructor taught him to take off and fly solely on instruments from the moment the runway lights disappeared from view on take-off until 500 feet above ground level.  From about 500 feet on the crosswind climb, he was taught to fly 75 per cent on instruments and 25 per cent by visual reference; on downwind, 50 per cent on instruments and 50 per cent visual, on base, 25 per cent instruments and 75 per cent visual.  The pilot was given two hours night dual flight instruction practising navigation by reference to navigational aids.  He was also trained in recovery from unusual attitudes at night.  His instructor advised that the pilot displayed good airmanship and a responsible attitude while under training.

During an interview after the accident, the instructor was asked what he thought the pilot would do if at 500 feet after take-off he looked out and found himself in cloud. The instructor replied that he thought the pilot would immediately descend to regain visual flight.

2. ANALYSIS

With pre-flight planning/preparation, early departure from Moorabbin, business meetings through the day and the 1948 EST estimated take-off time from Warrnambool, it is possible that the pilot was suffering from fatigue at the time of the accident.  However, the degree of fatigue and the degree to which it contributed to the accident remains unknown.

It also remains unknown how the onset of darkness and the degree of darkness hampered the pilot's ability to assess the amount and base of the cloud and/or the existence of drizzle in the circuit area immediately before take-off.

It is possible that the pilot first looked out at 500 feet after climbing on instruments and found himself in drizzle or in cloud, with limited or no external visibility. If this happened, it is likely that the pilot immediately descended to become visual and then attempted to return for a landing on runway 31.  This is consistent with witnesses seeing the aircraft flying at low level.

Why the pilot flew towards the centre of runway 31 immediately prior to entering a steep left spiral dive, could not be determined.  Perhaps low cloud or drizzle prevented the pilot from flying further downwind to position for a landing on runway 31, or perhaps he could have been positioning the aircraft for a departure.

As witnesses clearly saw the aircraft climb and then enter the spiral dive, it seems that the aircraft was not in cloud or drizzle for the spiral entry and subsequent descent.

The impact site was only 255 metres to the right of a row of the illuminated runway lights which should have given the pilot a visual reference to avoid the ground. There was no evidence of an attempted recovery from the left spiral dive.

Pilot disorientation is a possible reason for the spiral dive because conditions were dark and there was probably no visible horizon.  However, the aircraft was not in cloud or drizzle for the spiral and the accident occurred close to the illuminated runway, which should have given the pilot a reasonable visual reference to level the wings and attempt to recover from the dive.

It is also possible that the pilot suffered incapacitation during the flight.

3. CONCLUSIONS

3.1 Findings

1. The pilot was correctly qualified and endorsed to perform a night flight under visual flight rules, but his night flying experience level was low.
2. The pilot did not hold an instrument rating.
3. Weather forecasts, assessed by the pilot prior to take-off, indicated that the weather may have been suitable for night visual flight ahead of the cold front trough and behind it.
4. The accident occurred as a cold front was passing through Warrnambool.
5. There was a low cloud cover with associated drizzle in the area.
6. The aircraft was within its approved centre of gravity and gross weight limits at the time of the accident.
7. The fuel on board was of the correct type and of sufficient quantity for the flight.
8. No pre-existing fault was found with the aircraft which may have contributed to the accident.
9. The impact occurred close to and abeam runway 31 while the runway lights were illuminated.
10. The post-mortem carried out on the pilot indicated the presence of ischaemic heart disease may have contributed to the accident.

3.2 Significant factors

The factors which led to this accident could not be positively determined.  However, the three most likely factors are:

1. The pilot was suffering from fatigue at the time of the accident.
2. The pilot suffered some form of in-flight incapacitation.
3. The pilot lost control of the aircraft as a result of losing visual reference in adverse weather.

SAFETY ACTION

The Bureau of Air Safety Investigation is continuing to investigate a number of possible safety deficiencies in the operations area that have arisen from this accident. Any safety outputs arising from this investigation will be published in the Quarterly Safety Deficiency Report.

The flight was the second Metro III type-conversion training flight for the co-pilot. Earlier that night, he had completed a 48-minute flight.

During the briefing prior to the second flight, the check-and-training pilot indicated that he would give the co-pilot a V1 cut during the take-off. The co-pilot questioned the legality of conducting the procedure at night. The check-and-training pilot indicated that it was not illegal because the company operations manual had been amended to permit the procedure. The crew then proceeded to brief the instrument approach which was to be flown following the V1 cut. There was no detailed discussion concerning the technique for flying a V1 cut.

The co-pilot conducted the take-off. Four seconds after the aircraft became airborne, the check-and-training pilot retarded the left engine power lever to flight-idle. The landing gear was selected up 11 seconds later. After a further 20 seconds, the aircraft struck the crown of a tree and then the ground about 350 m beyond the upwind end of the runway and 210 m left of the extended centreline. It caught fire and was destroyed. The co-pilot and another trainee on board the aircraft were killed while the check-and-training pilot received serious injuries.

The investigation found that the performance of the aircraft was adversely affected by:

• the control inputs of the co-pilot; and
• the period the landing gear remained extended after the simulated engine failure.

The check-and-training pilot had flown night V1 cut procedures in a Metro III flight simulator, but had not flown the procedure in the aircraft at night. He did not terminate the exercise, despite indications that the aircraft was not maintaining V2 and that it was descending. There were few external visual cues available to the crew in the prevailing dark-night conditions. This affected their ability to maintain awareness of the aircraft's position and performance as the flight progressed.

A number of organisational factors were identified which influenced the aviation environment in which the flight operated. These included, on the part of the operating company:

• an inadequate Metro III endorsement training syllabus in the company operations manual;
• inadequate assessment of the risks involved in night V1 cuts; and
• assigning the check-and-training pilot a task for which he did not possess adequate experience, knowledge, or skills.

Organisational factors involving the regulator included:

• a lack of enabling legislation prohibiting low-level night asymmetric operations;
• deficient requirements for co-pilot conversion training;
• inadequate advice given to the operator concerning night asymmetric operations and the carriage of additional trainees on training flights;
• deficient training and approval process for check-and-training pilots; and
• insufficient quality control of the company operations manual.

The investigation also determined that there was incomplete understanding within the company, the regulating authority, and some sections of the aviation industry of the possible effects of engine flight-idle torque on aircraft performance. Inadequate information on the matter in the aircraft flight manual contributed to this.

Witnesses reported seeing the aircraft depart runway 28 and complete a full circuit without landing. At a height of approximately 400 to 500 ft above ground level as the aircraft was turning onto final approach during its second circuit, it entered a steep nose down spiral to the right. The spiral descent continued to the ground and the pilot received fatal injuries during the impact. The wind at the time of the accident was reported to have been from the north-north-west gusting to 45 km/h.

Four ladies had reservations for a helicopter scenic flight and were met in the airport terminal by the ground hostess for transportation to the helipad in the company bus.

The ground hostess stated that while proceeding to the helipad she briefed the ladies about the helicopter, and the safety requirements when in its vicinity.

She parked the bus on the road adjacent to the helipad, approximately 12 metres to the right and well forward of the helicopter. The ladies were then told to remain at the bus until instructed to approach the helicopter.

Following normal practice to save engine cycles, and turnaround times, the pilot left the helicopter engine running after landing, then locked the controls and got out to assist the ground hostess disembark the passengers, who were then directed to the bus. The ground hostess accompanied them as far as the edge of the main rotor disc, then signalled the ladies to follow her back to the helicopter.

One lady had expressed an interest to occupy the front left seat during the flight. This was agreed to by the other ladies.

The ground hostess watched the ladies follow her towards the helicopter, but when she turned her head to check its proximity, the lady, who had requested the front seat, left the group to pass behind the helicopter, and walked into the tail rotor, receiving fatal injuries.

The ground hostess stated that after the occurrence she spoke to the ladies, who confirmed that they had understood her briefings, and had no idea why the other lady had not followed her instructions.

Statements taken by the police did not address whether the ladies had received a safety, familiarisation briefing, but covered the last instructions given by the ground hostess concerning waiting at the bus and approaching the helicopter. Only two of the ladies could now remembered these instructions.

Reports indicated that three of the ladies were partially deaf, and the other had assisted them. Because of this it is possible they may have missed some parts of the briefing.

The company requires all staff to be aware of, and act in accordance with the requirements of the Civil Aviation Regulations and Orders, and the companies' Operations Manual, including all safety aspects. There was no evidence to indicate that the staff had not acted accordingly.

The reason why the lady departed from the group, and attempted to pass behind the helicopter was not established.

1. FACTUAL INFORMATION

Summary

The helicopter did not arrive at its destination following a ferry flight. The wreckage of the helicopter was found by chance, late at night. It had crashed during a dark night. The engine had stopped before impact. The helicopter fell several thousand feet out of control.

The investigation did not find any mechanical defects which could have contributed to the accident.

History of the flight

During the day, the pilot flew on mustering tasks and an hour's ferry flight from Avon Downs to Headingly station. There he refuelled the helicopter with 50 litres of aviation gasoline. None of the Headingly station staff had the opportunity to speak with the pilot during his short stopover, but they saw the helicopter depart to the south-east at 1700 EST.

At 1950, the manager of Brighton Downs station heard a message from the pilot on the station's citizen band radio. The pilot said that he was 4 NM from Pot Jostler outstation and that he could see the lights of the house. The manager replied that a kangaroo shooter and his family occupied the house and that he could get a meal from them. The last radio message from the pilot wished the manager good night.

At about 2100, the kangaroo shooter and his family were returning from a paddock about 20 km north of the outstation.  They saw a piece of Perspex lying on the access track about 5 km short of the house and recognised it as a part of a helicopter. A short search by truck headlights revealed a tail boom sticking out of the ground. They found the main fuselage of the helicopter some 300 m south of the tail boom.

The family said that they had not left any lights on at the outstation in their absence. The only lighting available was gas powered.

Weather conditions

Last light is regarded as the time when the ambient light value falls below that required for aircraft operating under day visual flight rules and is defined as the time when the setting sun is six degrees below the western horizon. Ambient light may be varied by a cloud cover which has the effect of bringing on an earlier last light. Last light at Pot Jostler outstation was calculated as 1832, 1 hour and 18 minutes before the pilot radioed Brighton Downs.

The Bureau of Meteorology analysis of the weather conditions agreed with reports from local observers. There was a cloud cover of five octas strato-cumulus, base of about 2,000 ft.  Above the lower layer of cloud was a higher-level alto-cumulus cover of five to six octas. Cloud obscured any starlight. The moon was in its last quarter and did not rise over the accident site until 2305. A ground observer stated that it was a very dark night without a visible horizon.

The wind at ground level was relatively strong and gusting at 10-20 knots from the south-south-east.

Whether the pilot obtained a weather forecast is not known.

The helicopter

The helicopter had undergone a periodic inspection on 14 July 1995 at the company's maintenance facility at Mt Isa. A new maintenance release was issued and was valid until 14 July 1996 or 595.2 hours total time in service. It was valid for day visual flight rules operations in the categories of private, aerial work, and charter. The helicopter's hour meter recorded 12.7 hours since the maintenance release was issued.

The helicopter was not fitted with attitude instruments essential for night operation. Along with other company helicopters, it was fitted with a global positioning system. The fitment allowed pilots to save flight time by being able to track direct to a destination over featureless terrain.

Flight fuel

Direct track distance between Headingly station and the crash site was 186 NM. Given a flight time of 170 minutes, the average groundspeed was calculated at 65 kts. Normal cruise speed is 80-85 kts true airspeed. The loss of 15-20 kts in ground speed confirmed the earlier weather assessment.  The helicopter's fuel endurance was approximately 3.5 hours from full tanks. Whether the pilot filled the tanks to capacity at Headingly station is not known.

Wreckage examination

The wreckage was scattered along a 1,000-metre trail, aligned with the prevailing wind, 165/345 degrees magnetic. The investigation team found small pieces of Perspex at the northern extremity of the trail and the tail boom was 300 m north of the main fuselage, which was the southernmost piece of wreckage. The fuselage gave the appearance of having been involved in a very heavy landing. It was upright but squashed to half its normal height. One complete main rotor blade and one half of the other were still attached to the mast. A remnant of the second blade had come to rest a short distance away. Both blades were bent. One blade was bent up, the other was S-shaped. The mast had been subjected to one severe mast bump. The base of one blade had crimped the mast. The main rotor blades had severed the tail boom and penetrated the cabin.

Those first at the scene said that there had not been any fuel smell. The main fuel tank was holed on impact, but the auxiliary tank was intact. The latter contained 1.5 litres, the equivalent of unusable fuel. Stretched light globe filaments revealed that the following warning lights were illuminated at impact: Clutch, Low Fuel, Low Rotor RPM, and Rotor Brake.  A later specialist metallurgical examination of crimped sections of exhaust manifold found that the manifold was cold at impact. The engine was stripped later in an engineering workshop, but nothing was found which could have prevented normal operation.

The flight manual warned that when the Fuel Low warning light illuminates, the pilot has five minutes to land the helicopter before fuel exhaustion.

Trajectory analysis of the wreckage trail found that the helicopter broke up between 2,400-2,800 ft above ground level.

Pilot experience

The pilot was first issued with a commercial helicopter pilot licence on 11 May 1993.  The company had employed him since 2 May 1995. He had previously been employed by a Western Australian pastoral company where pilots worked as ringers in a private operation. Another pilot from this Western Australian company reported that pilots were required to fly excessive hours per week, often beyond daylight hours.

When the present company's chief pilot gave him a check on company flying operations, the pilot indicated that he had previously flown a Robinson R22 helicopter at night. The chief pilot warned him not to continue the practice with this company. Extracts from his detailed notebook recovered from the wreckage indicated that the pilot had flown at night on two subsequent occasions. One entry, dated 23 June 1995, read: 'Left Serpentine at 5 pm for Pot Jossler (Jostler). Arrived at Pot Jossler in pitch dark at 7:10 pm. Flew last 20 min. at 4,500 ft so as not to run into anything'.

An inspection of his logbook revealed that the pilot had not received any formal training in night flying, nor had he logged any solo night flying.

The manager of Brighton Downs station said that the pilot had worked the property several times and was becoming familiar with it. The pilot had flown 11 hours on the day of the accident, a large proportion of it in mustering, which is a high workload task.

2. ANALYSIS

Conduct of the flight

The pilot's diary indicated that he had on occasions continued to fly the helicopter at night after joining his present employer. Company supervision had not been sufficient to discover these practices. The helicopter was not equipped with the necessary flight instruments to safely conduct flights after last light. It was fitted with a global position system navigational aid.

The terrain along track is relatively featureless and the area is poorly serviced by radio navigation aids. A global positioning system is a useful aid, but in this case, it would have enabled the pilot to continue flight after last light when navigation by other means was impossible.

Fuel

Those first at the scene could not smell any fuel. Subsequent specialist examination confirmed that the Fuel Low warning light was on at impact and the engine was cold, an indication that it had stopped. All evidence pointed to fuel exhaustion as the reason for engine stoppage. Disorientation

When the pilot radioed the manager of Brighton Downs station, he said that he could see the lights of the house. Since there were, in fact, no lights on at the house, the pilot must have seen some other light, perhaps a star visible through a small break in the cloud cover. Such a mistaken belief would have caused immediate disorientation by giving him a false horizon reference.

The sudden illumination of the bright Fuel Low warning light may also have contributed to the pilot becoming disorientated. This light, which is a bright red colour, is designed for daytime operation and cannot be dimmed. The pilot would have lost any outside visual reference in the low ambient light conditions following illumination of the warning light.

Either or both of the two events could have led to a loss of control. Such loss of control must have been sudden because the pilot did not transmit on the radio link established earlier.

Fatigue

Having flown for 11 hours, the pilot had exceeded the daily duty time limitations of Civil Aviation Order 48 by 2 hours. These limits were formulated to prevent pilots flying when fatigued. Such a long working day culminating in a stressful night flight could only have left the pilot fatigued. One of the most dangerous aspects of performance degradation with fatigue is that a person is unlikely to be aware of the manner and extent of this deteriorating performance (see F.H.Hawkins, Human Factors in Flight, Ashgate, Aldershot, 1987). Fatigue can result in a number of significant performance decrements such as poor self-monitoring, increased susceptibility to distraction, lowered arousal and increased reaction time.

3. CONCLUSIONS

3.1 Findings

1. The helicopter was certified for day, visual flight rules operations only.
2. The pilot had operated the helicopter at night.
3. The pilot was not qualified for night flying.
4. The night was very dark without a visual horizon.
5. The pilot was probably 'fatigued', having flown excessive hours that day.
6. The engine probably stopped due to fuel exhaustion.
7. The pilot probably became disorientated and lost control of the helicopter.
8. The rotor RPM decayed significantly.

3.2 Significant factors

1. The pilot continued the flight after dark when neither he nor the helicopter was equipped to do so.
2. The pilot probably lost control following fuel exhaustion.

An unregistered single-seat Sapphire ultralight aircraft took off from the town airstrip at 1700 EST. The pilot had borrowed the aircraft from the owner who expected him to practise flying the aircraft in the vicinity of a private airstrip at the outskirts of the town. At 1720 the aircraft crashed within 2 km of the town airstrip and about 500 m from the private airstrip.

This aircraft was unique. The designer had built it during the developmental stage of the aircraft type. Since then, it had been significantly modified including being retrofitted with a 40 horsepower Rotax 447 two-stroke engine, mounted upright. This is in contrast to the current Sapphire model which has the same Rotax engine installed inverted. The engine mounts were modified to enable the engine to be installed upright, and a specially designed engine cowl had been fitted. The shape of the engine cowl may have affected the aerodynamics of the aircraft.

Even though the propeller reduction gearbox had been installed inverted, the propeller thrust line was slightly higher than in the current model. The higher thrust line may have caused handling differences compared with the current model. The aircraft was fitted with a larger diameter propeller which rotated at lower RPM than propellers installed on current Sapphire models due to different gearing in the reduction gearbox. Whether the thrust produced was the same as the current model is unknown.

This aircraft did not have flaps and was fitted with full-span ailerons. Later Sapphire models have flaps and half-span ailerons. According to the current manufacturer, the full-span ailerons would have had a significant effect on the tendency for spin entry if the pilot inadvertently used aileron, in lieu of rudder, in an attempt to counteract wing drop. The main wing was fully fibreglass covered and appeared to be the same size and shape as the current model. The aircraft was equipped with a vacuum-driven airspeed indicator (ASI) sourced from a small venturi mounted on the nose of the aircraft. The owner had previously tested this ASI in flight and noted that it indicated 35 kts at the stall. Current Sapphires are fitted with a standard pitot/static system and the stall occurs at 36 kts.

The owner stated that when he test flew the aircraft it maintained straight and level flight, hands and feet off the controls, at 65 kts indicated airspeed. However, the effect of any differences between the accident aircraft and the current-model Sapphire concerning tendency to spin, spin entry, the established spin, or spin recovery is unknown.

The owner and the pilot had only flown this modified version of the Sapphire. The owner had a total flying experience of 80 hours in ultralight aircraft, with about 8 hours recent flying experience in the modified Sapphire. He stated that he had discussed the attributes of his Sapphire with the pilot before allowing him to fly it.

Witnesses saw the right wing drop and the aircraft enter a spin at a height estimated to have been between 200 ft and 500 ft. They heard the engine continue to operate until ground impact. One witness stated that the aircraft entered the spin from straight and level flight and spun three times before impact. Another witness stated that the aircraft may have just commenced a slight climb to the right when the right wing dropped and spinning commenced.

At the time of the accident the temperature was about 10 degrees C, the wind was a north-westerly at about 5 kts, and visibility was good with no sun glare because of high cloud cover. Official last light was 11 minutes after the time of the accident. The surrounding terrain was an obstruction-free mud flat.

There was adequate fuel on board and examination of the airframe and the engine found no defects which may have contributed to the accident.

The aircraft's centre of gravity and gross weight at the time of the accident are unknown. The owner and the pilot were unaware of the aircraft's empty weight and centre of gravity prior to the accident flight. Despite this lack of knowledge, pilots had successfully flown the aircraft for about 10 hours since it was modified.

According to other Sapphire pilots, the aircraft type does not exhibit a pre-stall buffet which would warn the pilot of an imminent stall. The Sapphire is not fitted with a stall warning horn. The investigation found that the pilot was wearing large boots and that the very small rudder pedals were located in a confined area of the cockpit pod. This may have made rudder application difficult. Spin recovery was probably not achievable if spin entry was as low to the ground as reported.

The pilot regularly flew his privately owned Jeep ultralight aircraft. Compared with a Sapphire, the Jeep has high drag, a slower cruise speed and a much slower stall speed. The pilot's logbook contained no entries for past Sapphire flights. However, according to the aircraft owner, the pilot had flown this aircraft four times and had accrued about two hours in it before the accident. None of the pilot's logbook entries indicated spin recovery training.

Spinning is currently banned in ultralight aircraft. However, the Australian Ultralight Federation's pilot ground training theory syllabus includes stall and spin recovery procedures, and the inflight stall training syllabus includes recovery from wing drops.

The Sapphire is known to be more sensitive to fly than the Jeep or similar high drag ultralights. It stalls at a higher airspeed and has sensitive handling characteristics. In the stall, the Sapphire normally mushes and then starts oscillating, but it may drop a wing and enter a stable spin. To stop the spin, a pilot must apply standard spin recovery drill. The manufacturer likens Sapphire handling characteristics to a modern glider. He recommends that, before flying a Sapphire, pilots should experience three hours dual instructional flying, including full spin recovery, in a two-place glider, or undertake equivalent training in powered aircraft.

The modified Sapphire stalled and entered a spin at a low altitude from which recovery was not considered possible. The reason the aircraft entered a spin could not be determined.

SAFETY ACTION

On 14 July 1995, the Australian Ultralight Federation (AUF) issued an Operations Bulletin to all training schools requesting them to ensure that the flight training syllabus coverage of stalling is followed. During routine inspections of operators, the AUF is ensuring that this is done.

The Operations Bulletin also requested instructors to impress upon students the need to undergo additional training when upgrading to a higher-performance aircraft. The aircraft manufacturer recommends three hours dual instruction in a glider prior to upgrading to the Sapphire.

History of the flight

The aircraft was one of a group of powered hang gliders operating from a 900-m grass strip aligned east-west. The group had arrived at the strip the previous morning. That afternoon, the pilot flew the aircraft with a passenger on a cross-country flight. Earlier, the pilot took another passenger for a flight which included power-on and power-off stalls. The aircraft performed normally on both these flights.

The group camped at the strip overnight and planned an early morning flight. However, the departure was delayed by fog. The aircraft had been left assembled overnight standing in the open. As a result, the wing had been wetted by condensation to the extent that beads of water had formed. Although the wing was exposed to direct sunlight for about 30 minutes before take-off, it was reported to have still been wet, although not beaded, when the aircraft taxied for take-off.

Conditions were suitable for flight by about 0930 EST. The understanding was that each aircraft would take off towards the west and climb straight ahead to 1,500 ft above ground level before flying back across the strip in an easterly direction.

The accident aircraft was the first to take off. The wind was calm. The aircraft became airborne after a normal ground roll and climbed straight ahead. As the climb progressed, the aircraft followed the normal procedure of positioning about 80 ft above the right side of the strip. (This procedure is conducted so that, in the event of an engine failure, the aircraft is in a position to turn left to land back on the strip.)

At an estimated 200 ft above ground level, the aircraft levelled and entered an abrupt right turn to head approximately north. At the same time, the engine noise decreased but then increased again as the aircraft began a shallow climb, still heading north. A short time later, the aircraft rolled sharply right to at least 45 degrees of bank and adopted a steep nose-low attitude. It then spiralled to the ground, completing about one and one-quarter turns before impact. Members of the group were in radio contact with one another. No transmissions were heard from the pilot during the take-off and accident sequence.

Witnesses described the turn onto north and the subsequent turn as unusually abrupt. One witness, who flew a similar aircraft, considered that the turns would have required considerable physical effort from the pilot to manoeuvre the control bar towards his chest and to the left. The pilot was described as confident and reliable. There were no reports of him acting impulsively while flying.

Assuming the aircraft was carrying full fuel for the flight, the calculated take-off weight was 387 kg. Maximum allowable take-off weight for the aircraft was 401 kg.

Wreckage examination

Examination of the wreckage did not reveal any pre-existing fault which might have contributed to the accident. Failures to the mast and front mast brace were caused by overload. A strip examination of the engine did not reveal any fault which may have precluded normal operation. Examination of a section of engine exhaust pipe confirmed that the engine was operating at impact.

Pilot's experience

The pilot had completed a training course on weight-shift aircraft (commonly known as Trike aircraft) about 18 months before the accident. This training was conducted in accordance with the Trike Pilot Training Syllabus issued by the Hang Gliding Federation of Australia (HGFA) and approved by the (then) Civil Aviation Authority. The pilot did not receive any training in recovery from spiral dives; nor did the syllabus include a requirement for such training.

Medical and pathological information

The pilot was reported to have been in good health on the morning of the accident. The passenger was suffering from a cold. Pathological examination did not reveal any pre-existing condition of the pilot or the passenger which might have contributed to the accident.

Extracts from Pilot's Handbook

Section 2, paragraph 2.1 of the Pilot's Handbook for the aircraft lists airspeed limitations including:

"Stall speed 30.3 knots (IAS) max weight (power off)

23.0 knots (IAS) min weight".

Paragraph 2.4, Other Limitations, includes the following:

"The effect of light rain on the aircraft is slight. Heavy rain will cause the stall speed to rise to the point where it is possible to stall the aircraft without banking the wing. Under these circumstances the pilot input for control in the roll axis increases.... Do not use waterproofing agents on the wing as the consequent beading of water droplets can significantly increase the stall speed.

Aerobatic manoeuvres including whipstalls, stalled spiral descents and negative G manoeuvres are not permitted. It must be emphasised that a whipstall, spiral descent, or negative G manoeuvre can never be conducted safely. These manoeuvres put the aircraft outside the pilot's control and puts [sic] both the aircraft and its occupants in extreme danger."

Aircraft handling characteristics

As part of the investigation, the Civil Aviation Safety Authority (CASA) was approached for information on the handling qualities of weight shift controlled (Trike) aeroplanes, including the type involved in the accident. As a result, a CASA test pilot undertook a limited flight evaluation and held discussions with experienced Trike pilots.

A test was conducted in which the aircraft was stalled and no roll correction applied. The Trike entered a spiral dive during which roll divergence and nose-down pitch increased. Large out-of-trim forces were felt as speed increased. This caused difficulty in maintaining a nose-up longitudinal control position. Roll control remained effective throughout the manoeuvre although response rate to a given control input decreased as the spiral developed. Rapid recovery from the spiral was achieved by relaxing the nose-up pitch input and rolling wings level.

The test pilot reported that discussions he had with experienced pilots indicated that the spiral dive was not a widely recognised condition among Trike pilots. If a wing drop at the stall was not corrected early, recovery from the spiral dive to normal flight could result in an altitude loss of up to 90 m. The recognition of, and recovery from, a spiral dive was not included in the Trike Pilot Training Syllabus. It was suggested that such training be included in the syllabus.

The test pilot considered that the accident aircraft may have stalled and entered a spiral dive. A reflex action of the pilot may have been to attempt to raise the nose of the aircraft to recover from the dive. However, although this would have involved very high control forces, such an action by the pilot would have maintained the wing in a stalled condition, causing the spiral to continue.

A further flight characteristic of the Trike was that aircraft response to control inputs was slower as speed decreased, and aircraft weight increased.

ANALYSIS

The evidence indicates that the aircraft entered a spiral dive which continued to ground impact. Without specific training in this area, the pilot probably did not have the experience or knowledge to apply to recover from the unusual situation the aircraft was in. From the witness reports, it could not be determined if the height above ground of the aircraft when it entered the spiral dive was sufficient to allow recovery to normal flight.

The two abrupt turns made by the aircraft shortly after take-off cannot be readily explained. The aircraft did not follow the planned departure procedure and there was no radio transmission from the pilot to indicate any problem. Further, the pilot had no record of impulsive behaviour during flight.

It is possible that the pilot was attempting to fly a circuit to land back on the strip, although no reason for such action was established. The take-off weight of the aircraft meant that the stalling speed was high. This may have been increased further by the remaining moisture on the wing. It is conceivable, therefore, that the aircraft stalled during the turn which led to the spiral.

It is also possible that the change in engine noise heard by witnesses when the aircraft turned onto north influenced the pilot's actions. However, the engine noise quickly recovered and there was no evidence of any fault in the engine. The change in noise could be explained by the pilot's foot slipping on the throttle pedal control. These facts weigh against the engine being a factor.

The flight tests indicated that wing drop accompanying a stall could lead to a spiral dive if roll correction was not applied. Although the response rate of the aircraft to control inputs would have been reduced at the operating weight of the aircraft, the pilot had recent experience in flying the aircraft (including stalling) at this weight. The entry of the aircraft into the spiral dive is, therefore, not readily explainable.

CONCLUSIONS

Findings

1. For reasons which were not established, the aircraft entered a spiral dive.
2. The pilot had not received training in recognising and recovering from spiral dives.
3. The height above ground available for the pilot to recover from the spiral dive was probably marginal.

SAFETY ACTION

During the investigation, close contact was maintained with the HGFA. The Federation was also informed of the results of the flight evaluation undertaken by CASA. In response to this information, the Federation issued in March 1996 an amendment to the pilot training syllabus for weight-shift aircraft to include steep turns as a training unit. One of the objectives of the unit is that the student demonstrate skills required to counter the spiral tendency of the aircraft following a stall during a steep turn.

A revised HGFA Weight shift Microlight Flying Instructor's Manual was issued. This included the following:

"Spiral Dive Tendency

Demonstrate the tendency for the aircraft to begin to "spiral" when excessive pitch pressure is applied with a nose down attitude in a steep turn. Demonstrate that the aircraft will recover from the spiral due to its pitch and roll stability, though height loss can be substantial if excessive pitch pressure is held until the aircraft stalls. Demonstrate that reducing pitch pressure and levelling the wings will reduce height loss.

"Demonstrate that though the aircraft's tendency to diverge in roll is slow, it will increase if the aircraft is held in this spiral mode. Demonstrate that the aircraft can be readily rolled level by easing pitch pressure and applying weight shift.

"Ensure that the student is able to recognise the onset of the spiral tendency and is familiar with the recovery techniques".

FACTUAL INFORMATION

History of the flight

The Cessna 310R aircraft had been chartered to transport livestock buyers and had flown from Wagga to Longreach on the afternoon of 27 July 1995. The three passengers and the pilot stayed overnight. The following morning the pilot had breakfast at about 0645EST. He was apparently well rested and appeared to be in good health. At about 0800 the aircraft departed Longreach and was flown to a number of properties in the Muttaburra and Julia Creek areas. This entailed a total of some 3 hours flight time before returning to Longreach at about 1500, where the aircraft was refuelled to maximum capacity. The pilot also obtained appropriate weather forecasts and route data, and submitted flight details to the Brisbane briefing office for an instrument flight rules flight to Wagga via Cunnamulla, Bourke, and Condobolin, at a cruising altitude of 9,000 ft. The estimated flight time was 248 minutes.

The pilot reported taxiing at Longreach at 1535 and subsequently advised a departure time of 1537. Normal position reports were made throughout the flight. At 1900, as the aircraft approached Condobolin, the pilot requested, and received, a report of the actual weather conditions at Wagga. The report indicated the wind was light and variable, and that there were 4 octas of cloud at 2,000 ft and 5 octas of cloud at 3,000 ft, with visibility greater than 10 km, reduced in isolated rain showers.

The aircraft passed over Condobolin at 1914, maintaining 9,000 ft, estimating Wagga at 1954. The pilot was requested by Sydney Flight Information Service (FIS) to contact Melbourne FIS. This was carried out at 1919:30 when the pilot reported maintaining 9,000 ft. Melbourne FIS advised the pilot to expect entry to Wagga controlled airspace on descent to 6,000 ft, and to contact Wagga Tower at 25 NM. This was acknowledged by the pilot.

At 1943 the pilot advised Melbourne FIS that the aircraft was 40 NM from Wagga and leaving 9,500 ft on descent. Shortly after, at 1943:35, Melbourne FIS asked him to repeat his DME (distance measuring equipment) distance from Wagga, to which the pilot replied, "about 37 DME". That was the last recorded radio transmission from VH-MFK. At 1948:46, three short bursts of hash and one click were heard, lasting for about 5 seconds. The pilot subsequently failed to contact Wagga Tower as required. Communications checks by both Melbourne and Wagga failed to re-establish contact with the aircraft. Search-and-rescue procedures were initiated which resulted in the wreckage of the aircraft later being found 55 km NNW from Wagga Airport, in a cleared field, in lightly timbered, generally level country.

It was subsequently reported that the wife of the pilot had made a telephone call from her home at Narrandera to one of the passengers, as the aircraft approached Wagga. The passenger handed the mobile telephone to the pilot, who told his wife, "I am in big trouble, I've lost my gyros". He indicated he may have to divert to Narrandera but was informed that the weather was not good there, either. His wife said she would go down to the airport at Narrandera and call him back. After a brief farewell, the pilot terminated the call and some 10 seconds later his wife, who was monitoring the radio, heard him report at 37 DME.

A pilot flying from Broken Hill in a similar aircraft type had landed at Wagga some 20 minutes prior to the accident. He reported that, at his cruising altitude of 9,000 ft, he had generally been above cloud but had occasionally flown through the tops of larger build-ups. The night had been very dark and the only ground lights he had observed were from Leeton. There had been little turbulence apart from the "odd bump", and he had observed only light rime icing on the airframe at cruising altitude. This had rapidly dissipated during descent through 7,000 ft.

Some time after 2000 he was requested to assist in the search for the missing Cessna. After taking off from runway 23 at Wagga, he entered cloud at about 1,000 ft and flew out along the expected inbound track of the aircraft to a distance of about 35 NM, at an altitude of 4,000 ft. He had then searched the area between 35 NM and 25 NM for about 20 minutes. At no stage during the time he was in the search area did he see the ground or any other feature.

The wreckage of the aircraft was strewn over an area of some 250 m by 300 m in a pattern consistent with an in-flight, high-speed breakup, at a low height. Apart from the rudder tab, all structural components and flight controls were accounted for at the accident site, including a 0.5 square metre section of the left horizontal stabiliser lower skin, which was located some 450 m to the south-west of the main wreckage area. From the depth of the impact craters, and orientation of ejected earth, it was apparent that the wreckage had been travelling at high speed on impact, in a north-east direction. The disposition of the tail components indicated they had separated first in the break-up sequence. The aircraft had then disintegrated prior to ground impact. This was indicated by the wreckage scatter and divergent paths of heavier components. There was no evidence found to indicate the presence of any pre-existing structural deficiency prior to the accident. Both engines had suffered considerable impact damage but had probably been at a low power setting at the time of impact. This was consistent with damage observed to the propeller blades. Evidence was found to indicate that all four fuel tanks had contained fuel at the time of impact.

All four occupants had suffered multiple injuries in the accident. The extent of aircraft damage made the accident non-survivable. Each of the three passengers had been ejected from the aircraft before it struck the ground, as a result of massive structural disruption of the airframe. None of the passenger seatbelts found in the wreckage showed evidence of having been fastened at the time of impact.

During an in-flight telephone conversation about 3 minutes prior to the accident, the pilot had indicated that the gyroscopic flight instruments had failed. Both attitude indicators and the directional indicator were air-driven gyro types. The turn co-ordinator was electrically operated. A post-accident examination of both attitude indicators showed no evidence of rotational witness marks which would have been expected if the gyros had been rotating at impact. The directional indicator gyro casing did display a witness mark consistent with the gyro being stationary at impact. Although it could not be determined if the turn co-ordinator gyro had been rotating at the time of the occurrence, electrical power was maintained until aircraft break-up.

The aircraft was equipped with two vacuum pumps, one driven by each engine, to provide a vacuum source for the air-driven gyroscopic flight instruments. The right engine driven vacuum pump body was found on the ground in the area between the engines. The left engine driven vacuum pump was found complete, together with its drive coupling, in the crater of the main wreckage. No useful information was obtained from the remains of the right engine vacuum pump. The left engine vacuum pump was dismantled, and the internal vanes were found broken, possibly resulting in seizure of the pump and subsequent shearing of the drive coupling. Further investigation indicated that the engine had continued to operate after the drive coupling had sheared. When that event took place could not be determined. It is likely that the right vacuum pump drive had also sheared in flight; however, this could not be substantiated as the drive coupling was not recovered. An examination of the remaining vacuum system components found no evidence of any pre-existing defect.

The loss of vacuum to the air-driven gyroscopic flight instruments would have resulted in those instruments providing erroneous and misleading aircraft attitude and heading indications to the pilot. A search of the BASI database found that four occurrences of double vacuum pump failure in twin-engine aircraft had been reported in Australia during the past 10 years.

A similar search was made of records held by the National Transportation Safety Board (NTSB) of the United States of America. In the period 20 May 1983 to 1 March 1994, the NTSB investigated 29 accidents in which vacuum system failure and/or vacuum pump malfunction were contributing factors. One accident involved a twin-engine aircraft suffering a double vacuum-pump failure. The remaining 28 accidents involved single engine aircraft. Most accidents resulted from the pilot losing control of the aircraft in instrument meteorological conditions (IMC), following the loss of reliable indications from the air driven gyroscopic flight instruments.

ANALYSIS

The circumstances of this accident were consistent with a loss of control by the pilot during flight at night in IMC, which resulted in the structural limitations of the aircraft being exceeded.

The pilot was reported to have told his wife, during an inflight telephone conversation that "I've lost my gyros". This was indicative of a failure of the vacuum-driven gyroscopic flight instruments. Examination of both attitude indicators and the directional indicator showed their respective gyros were not rotating at the time of impact. An examination of the vacuum system found that, with the exception of the vacuum pumps, it had been capable of normal operation immediately prior to impact. Only the left vacuum pump was recovered, and was found to have failed prior to impact. From the evidence available, it is concluded that the right vacuum pump had also failed some time prior to impact.

Despite extensive enquiries, no evidence was found to indicate the vacuum system was other than capable of normal operation when the aircraft departed Longreach for Wagga. There was no evidence found of any event during the subsequent flight which could have indicated when, or in what sequence, the vacuum pumps failed. With the benefit of hindsight, the only indication of a possible problem was the unexplained change in cruising altitude from 9,000 ft to 9,500 ft after the aircraft had passed over Condobolin. This could suggest that the pilot had already lost the use of his gyroscopic flight instruments and was endeavouring to remain above cloud until ready to commence descent into Wagga. At no stage did the pilot indicate to FIS that he was experiencing problems.

The pilot was faced with a relatively straight descent into Wagga, utilising the remaining flight instruments. Those instruments were, by their very nature, subject to various errors resulting from manoeuvres and other accelerations during flight. Such errors would be manifested as false, short-term indications. In normal instrument flying, those false indications could be resolved by reference to the gyroscopically stabilised attitude indicators or directional indicators.

Instrument-rated pilots are required to demonstrate proficiency in controlling their aircraft in normal flight manoeuvres and unusual attitude recovery techniques, with sole reference to the remaining flight instruments following a simulated failure of the primary attitude indicator. Normally, the failure is simulated by covering the instrument face. However, the person conducting the proficiency check is not permitted to simulate a failure of the primary attitude indicator in IMC or at night, unless that person has in view another serviceable attitude indicator. Furthermore, if a standby attitude indicator, powered from a different source to that of the primary attitude indicator, is available, then the person demonstrating proficiency is permitted to refer to the standby attitude indicator. There was no provision for the fitment of a standby attitude indicator to this class of aircraft.

In this occurrence the pilot was faced with the failure of both attitude indicators, as well as the directional indicator. Moreover, there was extensive cloud and rain on the intended descent track, the night was very dark, and there would have been almost no external visual cues to assist the spatial orientation of the pilot. In addition, the descent was at the end of a long and probably tiring day. Unfortunately, as distinct from a proficiency check, it is unlikely that the attitude and directional indicators were covered. In the course of his normal instrument scan, the pilot could not have avoided seeing erroneous attitude and heading indications from the failed instruments. His instrument scan pattern would have been developed over many thousands of flying hours, with great reliance on the attitude indicator. Such a habit could not easily have been modified to ignore the very powerful stimuli from the now unreliable attitude indicator. As a result, it is considered that the pilot, despite his very considerable experience, encountered circumstances that were beyond his capabilities. During the descent in IMC the pilot became spatially disorientated, leading to the loss of aircraft control, and in-flight break up.

SIGNIFICANT FACTORS

1. The probable in-flight failure of both engine-driven vacuum pumps, resulting in a loss of supply to the air-driven gyroscopic flight instruments.
2. Unreliable aircraft attitude and directional indications from the air driven gyroscopic flight instruments, which adversely affected the ability of the pilot in command to safely control the aircraft by sole reference to the remaining flight instruments.
3. Adverse meteorological conditions which prevented the pilot in command continuing the flight by visual reference to the natural horizon or other external features, following the loss of credible indications from the air-driven gyroscopic flight instruments.

SAFETY ACTION

As a result of the investigation into this occurrence, the Bureau of Air Safety Investigation issued interim recommendation IR950059 to the Civil Aviation Safety Authority (CASA) on 21 October 1996:

"The Bureau of Air Safety Investigation recommends that the Civil Aviation Safety Authority ensure appropriate maintenance policies are developed for all general aviation aircraft pneumatic vacuum system components".

The CASA response received on 13 February 1997 stated:

"I refer to your BASI Interim Recommendation IR960059 concerning the accident involving Cessna 310R, VH-MFK on 28 July 1995. The following comments are forwarded for your consideration.

"Upon receipt of this Interim Recommendation, CASA was alerted that maintenance requirements for pneumatic check valves had been introduced by Airborne Air and Fuel Products.

"An article is being prepared for inclusion in Flight Safety Australia informing all Certificate of Registration holders that periodic testing of specific vacuum components is recommended by the component manufacturer.

"An Airworthiness Advisory Circular will be issued to inform operators that failure to carry out periodic testing could result in unreliable indications or loss of aircraft flight instruments during IFR flight. This AAC will recommend that functional testing of the vacuum and pressure valves be included in the aircraft maintenance schedule."

Response status: CLOSED - ACCCEPTED

In addition, the Bureau issued safety advisory notice SAN960145 to the Civil Aviation Safety Authority on 13 February 1997:

"The Bureau of Air Safety Investigation advises the Civil Aviation Safety Authority of the availability of standby and alternative power sources for air driven gyroscopic flight instruments used in commercial IFR operations. An example of such a standby attitude reference system is the SVS III manufactured by Precise Flight Inc. This system utilises engine manifold pressure as a standby power source.

"The Authority should review the requirements for attitude indicators and examine the availability of alternative power sources. Also, during instrument ratings and renewals, pilots should be warned of the distractions caused by erroneous attitude indications and be encouraged to cover these instruments in the event of a failure."