Loss of control

Summary

The flight was planned as a regular public transport flight from Williamtown to Lord Howe Island. After departure, the pilot reported to Sydney Flight Service that he intended climbing to flight level 230. However, as the aircraft passed flight level 200 the pilot advised flight service that he was now climbing to flight level 210.

The pilot did not report at the first scheduled position code named 'Shark' on time but subsequently advised that he was descending to flight level 130. Shortly afterwards, the pilot reported having crossed 'Shark' and provided an estimate for the next scheduled position, 'Shrimp'. He also stated at this time that the aircraft was maintaining flight level 160. No further communications were recorded by Air Traffic Services from the aircraft. However, during the above period the pilot was in radio communication with two other company aircraft, both bound for Lord Howe Island. One aircraft was crewed by the company managing director and the company chief pilot.

When Sydney Flight Service did not receive the 'Shrimp' position report communications checks were commenced, and following the failure of these checks to establish contact with the aircraft, a search-and-rescue uncertainty phase was declared.

After the managing director arrived at Lord Howe Island, he contacted Melbourne Rescue Co-ordination Centre in response to a request from that centre and inquired about the aircraft. The crews of both other company aircraft subsequently reported hearing a radio transmission from the pilot of VH-SVQ stating that he had 'lost it'.

An extensive air and sea search failed to locate the aircraft or its occupants. Only a small number of pieces of the aircraft were found floating on the sea surface.

The investigation determined that the flight was not a regular public transport flight as the company did not hold the required approval from the New South Wales Air Transport Council to operate such flights over the Williamtown to Lord Howe Island route.

The factors that directly related to the loss of the aircraft could not be determined. However, a number of factors relating to the operation this flight, the operation of the company and the oversight of that operation by the regulator were identified.

The report concludes with a number of safety recommendations.

1. FACTUAL INFORMATION

History of the Flight

The aircraft had returned to Walgett late on the afternoon of the day before the accident, having completed a five-day charter to the Gulf of Carpentaria.

On the day of the accident the Walgett Aero Club held a barbecue and flying competition. The pilot of the Cessna 337 indicated that he did not intend to take part in this competition. Later in the day, he advised the flying instructor who was supervising the flying competition that he wished to carry out a low pass over the aerodrome. The instructor had no objection to this request.

At approximately 1550 hours the pilot took off from runway 18 with three passengers. After what appeared to be a normal circuit and approach, the aircraft made a high-speed pass, with the landing gear retracted, parallel to runway 18 at approximately 20-30 ft above ground level (AGL).

At 100-150 m from the runway intersection, witnesses observed the aircraft enter a steep climb. Witness estimates of the attitude adopted by the aircraft ranged from 40 to 70 degrees nose-up. The aircraft remained in this high nose attitude for 6-10 seconds until an altitude of approximately 700-1,000 ft AGL was reached.

At this point the aircraft's left wing dropped, the nose lowered steeply, and witnesses noted that the engine noise reduced significantly. The instructor supervising the competition stated that after the aircraft appeared to stall, he saw the rudder surface on the tailplane fully deflect in a direction opposite to the observed rotation. The aircraft rotated slowly to the left in an extreme low-nose attitude. Another witness commented that when the aircraft had descended to approximately 200-300 ft AGL, it appeared to adopt a slightly higher nose attitude. This change of attitude was transitory. The nose attitude lowered again quickly, and the aircraft impacted the ground in a very steep nose-down attitude.

Wreckage Examination

The wreckage was located on the Walgett aerodrome, 42 m to the south of the runway strip markers of runway 36.

The aircraft had impacted the ground in a steep nose-down attitude, wings level, with negligible rotation after impact. It did not slide along the ground after impact. The structural deformation was related to the onset of impact loads.

All aircraft extremities, including doors and all control surfaces, were present in the wreckage.

Technical examination of the engines and propellers showed them to be capable of normal operation prior to the impact. No indication was found of any aircraft system malfunction which may have contributed to the accident. However, destruction of the cockpit and the instruments precluded the individual systems' pre-impact status being determined.

The accident was not survivable.

Pilot Information

The pilot was the holder of a commercial pilot licence (aeroplanes). He held a valid medical certificate with a requirement to wear glasses. He was also the aircraft owner. He held an air operator's certificate, re-issued by the Civil Aviation Authority on 30 June 1994, which allowed him to carry out charter operations in VH-DRI.

The last entry in the pilot's logbook was made on 23 August 1994. At this time, he had accumulated approximately 3,200 hours total flight time (3,100 hours in single-engine aircraft and 3,050 hours as pilot in command).

The pilot had completed his endorsement training on the C337A on 11 June 1994. This was his first multi-engine endorsement. At the time of the last logbook entry, he had accumulated 102 hours in the aircraft type, most of which was in VH-DRI.

On 27 June 1994 the pilot undertook a flight check with a Civil Aviation Authority flying operations inspector in order to complete his chief pilot requirements and to include the C337A on his air operator's certificate.  On this occasion it was considered that the pilot met requirements but was to complete further training in the handling of emergency procedures. The CAA pilot file notes that an approved air test officer completed this training and advised that the pilot's handling of emergency procedures was satisfactory. The variation on the air operator's certificate was issued on 30 June 1994.

Post-mortem examination of the pilot revealed the presence of marked atherosclerosis of the coronary artery but there was no evidence of a coronary occlusion. Some alcohol was detected in liver and muscle fluid which was used for testing as sampling of blood or vitreous humour was not possible.

Weather

The weather on the day of the accident was mild with a temperature of 23 degrees C. A high-pressure system was located over south-east Australia.  The sky was clear and there was a gentle breeze from the south-west of up to 5 kts. The visibility was good.

2. ANALYSIS

Aircraft Handling Characteristics

Cessna aircraft are generally docile in most areas of handling. A number of pilots who had extensive experience on the C337, including flight instructors, agreed that placing the aircraft in the attitude that was witnessed on the day of the accident would have resulted in a much more aggravated stall than would be experienced as a result of a stall from straight and level flight. Witness statements agree that the aircraft was being operated at or near full power during the manoeuvre. It could not be ascertained whether the pilot reduced power before or after the point of the stall.

As the aircraft was seen to adopt and maintain a very high nose attitude, the stall that resulted would have occurred quickly due to the rapid loss of airspeed. The height required to recover from such a stall would have been significant and probably greater than that which was available.

The observed full deflection of the rudder surfaces was consistent with the actions of a pilot who may have been attempting to counter an incipient spin.

The C337A was certified under the United States Civil Aviation Regulations Part 3 which preceded the Federal Aviation Regulations Part 23.  As this aircraft was considered a multi-engine aircraft, it was not required to undergo spin testing as part of its type certification. Consequently, no data is available to indicate the typical height loss expected as the result of a spin.

VH-DRI was certified for operations in the normal category. The flight manual stated that operation shall be limited to normal flying manoeuvres but may include straight and steady stalls and turns in which the angle of bank to the horizontal is 60 degrees or less. Other acrobatic manoeuvres shall not be performed.

The Australian Civil Aviation Regulations define aerobatics as "manoeuvres intentionally performed by an aircraft involving an abrupt change in its attitude, an abnormal attitude, or an abnormal variation in speed". A glossary of aeronautical terms used for accident investigation by the US Department of Transportation Safety Institute, Oklahoma, defines an aerobatic manoeuvre as "a pre-planned flight manoeuvre in which the aircraft exceeds either 60 degrees of bank or 30 degrees of pitch".

The observed manoeuvre is consistent with the pilot's probable intention to attempt a wingover or possibly a stall turn. By any of the above definitions, wingovers and stall turns are aerobatic manoeuvres and are outside the normal flight envelope for this aircraft type.

Fuel System

VH-DRI was equipped with a main fuel tank of 174 litres usable fuel capacity in each outboard wing panel and a sump tank of 2.7 litres fuel capacity in the lower portion of each tail boom. Fuel flows to the sump tanks via two outlets in each main tank, one at the bottom forward edge and one at the bottom rear edge of each tank. Fuel then flows from the sump tanks through a bypass in each electric auxiliary fuel pump (when the pump is not operating) to selector valves located at the wing roots.

The inclusion of sump tanks reduces the risk of interruption of the fuel flow when the aircraft is placed in a range of flight attitudes including those that were witnessed during the accident. Had fuel been unable to drain from the main cells to the sump tanks due to the observed manoeuvre, it would have taken approximately two minutes and thirty seconds to unport the fuel lines in the sump tanks with the aircraft operating at full power, assuming that the sump tanks were full at the time the aircraft entered the nose-high attitude. As witnesses reported that the elapsed time between the aircraft entering the pull-up and the nose lowering at the top of the manoeuvre did not exceed 10 seconds, it is unlikely that engine failure would have occurred as a result of interruption to the fuel flow due to unporting of the fuel outlets from the main fuel cells.

VH-DRI was also equipped with an optional auxiliary fuel tank (68 litres usable capacity) in each wing between the cabin and the tail boom. The auxiliary tanks feed directly through the engine-driven fuel pump to the engine. The fuel from each auxiliary tank drains via a single outlet near the bottom of the tank approximately halfway between its forward and aft edges.

If the auxiliary tanks were selected it might be possible, at very low fuel levels, to unport the outlet to the tanks if the aircraft were in a very nose-high attitude for a considerable length of time.

The C337A engine is fuel injected. The fuel injection system delivers fuel, under pressure, to the inlet manifolds of the engine and is unlikely to be affected by the placement of the aircraft in unusual attitudes.

It was not possible, due to the severity of the damage, to accurately determine the position of the fuel selectors in the cockpit prior to impact. The flight manual stated that main fuel tanks should be selected for take-off, landing and the first 60 minutes of flight. It is therefore most likely that the main tanks were selected for this flight. Calculations have determined that there was approximately 150 litres of fuel on board the aircraft prior to its last flight. It was also not possible to accurately determine the quantities of fuel in each tank as every fuel cell was ruptured on impact with little or no fuel being observed in each cell. Nonetheless, it is unlikely that either engine failed due to fuel starvation.

Weight and Balance

Calculations of the weight and balance of the aircraft were based on the following:

1. The pilot was in the front left pilot seat while the three passengers occupied the right front seat and the two centre seats directly behind.
2. According to fuel agent records, the pilot purchased fuel at Birdsville but did not purchase fuel after return to Walgett. The aircraft flew direct from Birdsville to Walgett, a flight time of four hours. Assuming full tanks at Birdsville and a fuel consumption of 85 litres per hour (based on the pilot's operating handbook), fuel remaining at Walgett was calculated at 154 litres. After return to Walgett the pilot told the passengers that the aircraft had consumed 90 litres per hour. The pilot also informed the instructor supervising the flying competition that the aircraft had approximately 150 litres of fuel on board.
3. A bag of flour was found in the cabin area of the aircraft.  It was estimated to have weighed 20 kg.

Using these figures, it was determined that the aircraft was within weight limits but that the centre of gravity (c.g.) was outside limits, marginally forward of the c.g. envelope.

Having more or less fuel on board would not have significantly affected this result, with the c.g. close to or just forward of the c.g. envelope.  The only factor that would have made a significant difference to the position of the

c.g. would have been the seating position of the passengers. Had they been seated in the rear row of seats or some combination of centre and rear seats, the position of the c.g. would have moved to within the envelope.

Despite this finding, discussions with C337 pilots indicate that it is unlikely that the forward position of the c.g. had a significant effect on the handling characteristics of the aircraft.

Seat Mechanism

There have been documented occasions when control seats have dislodged from their previously locked position and moved backwards when loads have been imposed by rotation for take-off, or by g-loads in aerobatic manoeuvres or in turbulence. This has been attributed to excessive wear in the seat adjustment mechanism.

A sudden rearward movement of the seat could make it difficult for the pilot to reach the control column. There is also the possibility that the pilot could instinctively grab at the control column in an attempt to counter the seat movement, causing an abrupt nose-up change in attitude.

The Civil Aviation Authority issued an Airworthiness Directive (AD) in relation to the seat adjustment mechanism in September 1988 (AD/CESSNA 337/27 Amt. 1 Seat Adjustment Mechanism). This AD was required as a periodic inspection every 100 hours or 12 months, whichever occurred earlier.

The aircraft logbook indicated that the AD had been complied with. The most recent inspection was carried out on 5 July 1994, approximately three months prior to the accident.

Due to the severity of the damage to the cockpit area, it was not possible to determine if the seat had dislodged, in flight, from the desired position.

Pilot Performance

Estimates of any degree of pilot performance degradation due to the presence of alcohol in liver and muscle tissue should be treated with caution. It was therefore not possible to accurately determine the blood alcohol level.

There was no evidence to suggest that the pilot had consumed alcohol on the day of the accident.

There was no evidence that pilot incapacitation was a factor in the accident.

Weather

The weather was not considered to be a contributing factor to this accident.

Summary

As the aircraft was observed to adopt a very nose-high attitude and to sustain it, airspeed would have reduced significantly. As the pilot attempted to turn out of the nose-high attitude, the observed subsequent flight path of the aircraft was consistent with a stall and spin. The altitude of the highest point in the flight path was insufficient to permit the pilot to effect a recovery from a spin.

Loss of engine power at or near the highest point in the flight path would have reduced the power available during the manoeuvre intended to bring the aircraft out of the nose-high attitude. This could have increased the rate of airspeed loss and may have slightly advanced the time at which control was lost. It is doubtful, however, that an engine failure would have precipitated the loss of control.

3. CONCLUSIONS

Findings

1. The pilot held a valid licence and was endorsed on the aircraft type.
2. The pilot carried out a manoeuvre for which the aircraft was not certified.
3. The aircraft appeared to stall at the highest point in its flight path.
4. The aircraft descended in a steep nose-low attitude and impacted the ground shortly after.
5. The aircraft was within maximum weight limits.
6. The centre of gravity of the aircraft was marginally forward of the forward limit of the c.g. envelope.
7. The engines and propellers were capable of delivering power prior to impact.
8. No other pre-existing airframe or system malfunction that could have directly affected the flight was found.
9. There was no evidence of a medical condition that could have affected the pilot's ability to control the aircraft.

Significant factors

The pilot lost control of the aircraft at an altitude which was insufficient to permit a recovery before the aircraft impacted the ground.

The aircraft was operating from a 400 m grass airstrip orientated approximately 080 degrees M. The strip was on a property where the aircraft had been in storage for some six months prior to the accident. However, the pilot flew the aircraft for about 1.5 hours a few days before the accident. This activity included a flight to Mareeba Airport where the aircraft landed and the pilot borrowed some tools, including a soldering iron, to work on the aircraft. No information about the work done was available. However, the aircraft later departed Mareeba and apparently functioned normally during the return flight to the property.

On the day of the accident, the pilot secured two jerry cans of fuel in the right seat of the aircraft and placed two carry bags on the shelf behind the seat. The pilot indicated to witnesses that he intended to fly one circuit and land, bid farewell to those at the strip, and then depart for Innisfail, his first intended landing point.

A witness reported that the pilot started the engine and allowed it to idle for between 3 and 5 minutes before commencing the take-off. As the aircraft accelerated for take-off, it drifted towards the left side of the strip, but the pilot corrected this, and the aircraft became airborne. The witness, who had observed the aircraft take off from the strip a number of times, considered that the length of strip the aircraft used to become airborne was greater than he had observed on previous occasions. He believed, also, that the aircraft did not climb as well as usual and was making little headway against the wind. At an estimated height of 20 m above ground level, the aircraft entered a left turn at about 30 degrees angle of bank. When heading approximately north-west, it suddenly rolled further left and spiralled to the ground.

The Bureau of Meteorology advised that, based on observations taken at Mareeba Airport on the day of the accident, the estimated weather conditions around the time of the accident were: wind, south-easterly at 5-10 kt, temperature 19-20 degrees C, and relative humidity 80 percent.

Reports from Mareeba Airport indicated that the wind was gusty at times during the day, making the conditions unsuitable for circuit flying. Witnesses at the accident site reported the weather conditions as a light south-easterly breeze with occasional drizzle, although the sun was shining when the aircraft took off. This information appears to be supported by a photograph taken of the aircraft shortly before take-off. However, other photographs taken shortly after the aircraft took off, and looking towards the south-east, show a darkened sky and low cloud.

Examination of the aircraft wreckage did not reveal any abnormality which might have contributed to the accident. Metallurgical examination of a section of the exhaust pipe confirmed that the engine was developing power at impact.

The aircraft engine was fitted with a carburettor heat control. This was found in the off position during the wreckage examination. The atmospheric conditions which existed at the time of the accident were such that serious carburettor icing was likely at idle engine power. It is possible, therefore, that there was a buildup of carburettor ice in the period the engine was idling before take-off. However, any such buildup would cause a decrease in engine performance by lowering the available maximum RPM, an effect which would be evident to the pilot via the cockpit engine instruments. The photographs referred to above show that the aircraft became airborne well before the end of the strip. The presence of carburettor icing cannot, therefore, be confirmed. However, any reduction in engine power would have reduced aircraft performance, particularly during a climbing turn.

The described behaviour of the aircraft in spiralling to the ground is typical of loss of aircraft control following wing stall. The height at which the event occurred would have precluded recovery to normal flight.

A further possibility is that the aircraft was affected by a change in wind conditions or turbulence and that the pilot lost control of the aircraft in these changing conditions.

Factors

The following factors are considered relevant to the development of this occurrence:

1. For reason(s) which could not be positively determined, the pilot lost control of the aircraft during a climbing turn after take-off.
2. The height at which the loss of control occurred precluded the pilot recovering the aircraft to normal flight.

Factual information

The glider was launched by aerotow for a local flight and at about 2,000 ft it was observed by the tug pilot to release and to fly straight and level.

Sometime later, the pilot a of glider flying in the Waikerie circuit area reported that there was a damaged glider in a field about 3 km south of the airfield. The tug pilot immediately commenced an aerial search and on locating the severely damaged glider, alerted emergency services. The pilot had not survived the impact.

On-site examination of the wreckage indicated that the glider had impacted the flat, grass covered terrain at high speed in a vertical, or near vertical dive. There was no evidence that the aircraft had been rotating immediately at impact and all aircraft components were located at the site except for the radio battery. Impact forces had destroyed the cockpit area, partially detached both wings, and broken the fuselage near the wing trailing edge.

The wreckage was recovered to a hangar at the airfield and inspected by engineers. Despite the extreme disruption of the airframe, all primary control system components were identified and examined. Many components had fractured during impact, however, it was determined that the control systems were all correctly connected prior to impact. The damage to componentry precluded a conclusive examination for jamming or obstruction of the control systems. The radio battery location was in an area of the aircraft well away from the control systems. The battery to electrical system connector wiring was found torn apart, consistent with separation of the battery from the aircraft at impact.

The glider had a valid maintenance release, and no maintenance deficiencies were identified. No evidence was found to suggest that a pre-existing failure of an aircraft component contributed to the accident.

The pilot was one of a group of foreign glider pilots visiting Waikerie for a period of intensive flying. He was correctly licensed and endorsed on the type. Prior to being approved to conduct solo flights at Waikerie, he was given flight instruction which included stall and spin recovery techniques.

A witness reported that on the day before the accident, a similar glider flown by the same pilot had pitched steeply nose-down and lost height immediately after release from the aero-tow.  The pilot was severely shaken, and he was subsequently debriefed by instructional staff before undertaking further flying.

The tow had appeared normal to the tug pilot who also briefly observed the glider in straight and level flight following the release. The descent was apparently not observed; however, in the light of the witness report of the previous day's incident, the possibility that the pilot lost control of the glider cannot be discounted.

The reason for the dive and the inability of the pilot to regain control of the glider could not be determined.

After an uneventful flight from Merimbula, the pilot overflew the airstrip to check the windsock. He noted that the windsock was swinging erratically around a mean direction of about 30 degrees left of the strip direction (approximately 140 degrees magnetic). The pilot then positioned the aircraft on the downwind leg to land towards the south-east.

Neither the pilot nor the surviving passengers reported any significant turbulence during the circuit. The pilot indicated that he was aiming to touch down about 100m in from the end of the strip. At what he thought was about 100 feet above the level of the strip, at an indicated airspeed of 85-90 kt, and with full flap selected, the aircraft rapidly lost altitude and landed very heavily a short distance in from the end of the strip. It then bounced, becoming airborne again.

The pilot reported that he was startled by the heavy landing. When the aircraft became airborne again, he momentarily applied power to go around but saw that the aircraft was headed towards trees, so he closed the throttle. His memory from this point was not complete but he did recall applying full right rudder, with no apparent effect, as the aircraft headed towards the trees. He also recalled the stall warning operating twice - once during the sink which led to the heavy landing, and again when the aircraft bounced.

Examination of the scene of the accident revealed that after the aircraft bounced, it contacted the ground again, left wing tip first, about 150m beyond the initial impact point and heading towards the left side of the strip. By this stage, the aircraft had developed a marked right skid. It continued in this manner across a dirt mound at the left edge of the strip and struck trees. The principal impact occurred when the aircraft fuselage just forward of the right-wing root struck a large tree, causing severe deformation to the right-side cockpit area.

The aircraft was equipped with an autopilot and a yaw damper. The pilot had conducted the cruise section of the flight with both these aids engaged. On arriving overhead, the strip he had disengaged the autopilot via the control wheel disengage switch. In normal operations, this switch also disengages the yaw damper. On this occasion, the pilot had checked that the autopilot had disengaged but did not confirm the yaw damper had disengaged. The pilot expressed the view that the difficulty he experienced in attempting to regain directional control when the aircraft was heading towards the left side of the strip could have been due to a problem with the yaw damper. However, a check of the yaw damper system after the accident did not reveal any faults.

The surface wind at the time of the accident was estimated by the Bureau of Meteorology to have been 110/15 knots.

The sequence of events described by the pilot indicates that the aircraft probably encountered windshear or a downdraft on late final approach. Given the prevailing wind conditions and the local topography, either of these phenomena could have been present. The pilot's recollection that he heard the stall warning sound during the bounce, plus the fact that the aircraft then contacted the ground left wing tip first indicate that the aircraft probably stalled during the bounce (possibly as a result of the pilot closing the throttle), causing the left wing to drop. The effect of the left wing tip dragging on the strip surface would have been to yaw the aircraft further (i.e. exacerbate the right skid). The decreasing speed of the aircraft as it headed towards the edge of the strip, along with the large skid angle, would have reduced rudder authority. This would then have prevented the pilot regaining directional control of the aircraft.

The factors considered relevant to the development of the accident were:

1. Windshear or downdraft conditions caused the pilot to lose control of the aircraft on late final approach.

2. The aircraft probably stalled during the bounce after a heavy landing, causing the left wing to contact the runway and the aircraft to yaw further left.

3. A severe right skid and decreasing speed reduced rudder effectiveness and prevented the pilot from regaining directional control.

The aircraft was engaged on an IFR freight operation from Bankstown to Canberra and return. The flight from Bankstown to Canberra was uneventful and the aircraft subsequently departed for Bankstown at 1836 ESuT, carrying about 45 kg of light freight. A flight plan submitted by the pilot indicated the aircraft was to track via Shellys at 7,000 ft, thence to Bankstown outside controlled airspace (OCTA).

The pilot reported to Sydney Flight Service over Shellys at 1900, maintaining 7,000 ft, and estimating Bankstown at 1927. Three minutes later the pilot reported commencing descent, and subsequently reported on descent to Flight Service at 1906 after a frequency change. No further radio transmissions were received from the aircraft. Weather reports indicated that instrument meteorological conditions were prevailing in the area at the time.

The wreckage of the aircraft was located the following afternoon on the eastern slope of Axehead Mountain at an elevation of about 2,145 ft. The damage to the aircraft was consistent with having struck trees at cruising speed in straight and slightly descending flight, on a track of about 2930M. Both fuel tanks were completely disrupted, and the wreckage had been largely incinerated in the subsequent fire.

Later examination of the wreckage indicated the aircraft had been capable of normal operation at the time of the accident.

Recorded radar data showed that at 1906 the aircraft was tracking inbound on the 2200 radial of the Sydney VOR at a range of 50 NM, and passing through an altitude of 5,600 ft. When the aircraft was at a range of about 40 NM from Sydney, at an altitude of about 4,300 ft, it was observed to turn left and take up a track of about 2900, still gradually descending. The aircraft continued to maintain this track for a further 22 NM before it faded from radar. The last recorded altitude was at 2,900 ft. At the time of the accident the aircraft was OCTA and not under radar control. Radar returns from the aircraft transponder were suppressed from radar displays to reduce clutter, in accordance with normal operating procedures.

An examination of the medical history of the pilot showed no evidence of any cardiovascular disease or cerebrovascular disease risk factors. He was aged 49 years and held a current Class 1 medical certificate. An ECG performed at his last medical examination indicated a slight conduction defect, but in the absence of other indications of cardiovascular disease the pilot was assessed as fit.

From the evidence available, the flight path of the aircraft was consistent with the pilot becoming incapacitated as the aircraft descended towards Bankstown. The left turn at 40 NM from Sydney onto a heading of about 2900 is considered to have been unintentional as the subsequent track, which was about 1000 left of the flight planned track, took the descending aircraft towards mountainous terrain which was obscured by low cloud. The final track was not directed to any known tracking aid.

Significant Factor

The pilot probably suffered a sudden incapacitation during flight which rendered him incapable of continuing to safely operate the aircraft.

The purpose of the flight was to conduct an aerial inspection of a corn crop located approximately 1 km east of the airstrip. Witnesses reported seeing the aircraft in straight and level flight at a height of about 500 ft and hearing a change in the engine noise. A short time later, the right wing dropped, and the aircraft entered a steep, nose down, spiral descent which continued to ground impact.

Examination of the accident site showed that the aircraft had struck the ground while inverted and in a steep nose-down attitude while rotating to the right. The nature and extent of damage to the propeller indicated that the engine was developing significant power at impact. Inspection of the wreckage revealed no faults which might have contributed to the accident.

The evidence suggests that the aircraft probably stalled, causing the right wing to drop and a spiral dive to develop from which the pilot was unable to recover in the height available. The reason for the aircraft entering the manoeuvre was not determined.

Factors

1. The aircraft probably stalled, resulting in a spiral dive developing.

2. The pilot was unable to recover the aircraft to normal flight in the height available.

The aircraft was being flown to Coffs Harbour in preparation for an open day, during which the aircraft was to be displayed on the ground and in the air. Witnesses at Ballina observed the aircraft take off and conduct a circuit before flying low along the strip in the take-off direction. The aircraft then pulled up to about 75 degrees nose up, levelled at about 350 ft, and descended again while travelling in the same direction. It then accelerated, turned right, climbed to about 500 ft and departed in the direction of Coffs Harbour.

Witnesses at Coffs Harbour saw the aircraft approach the aerodrome from the west, cross over the main runway, turn right and fly south. The aircraft was then observed to turn north and approach the airfield at low level before abruptly entering a very steep climb. At an altitude estimated by some witnesses as between 200 and 400 ft above ground level, the aircraft rolled right before diving vertically towards the ground and disappearing behind trees. A short time later, the sound of impact was heard, and smoke was seen rising above the trees.

Examination of the accident site revealed that the initial impact occurred when the aircraft struck 8m high trees. This ruptured the right fuel tank, providing the fuel source for the fire. Examination of the burnt-out wreckage indicated that at ground impact, the aircraft was yawing right and skidding left. The aircraft struck the ground with about 7 degrees of left bank, a level nose attitude and low horizontal speed. The engine was operating at low power at the time of impact.

Of the two occupants of the aircraft, one held a commercial pilot's licence and the other a student pilot's licence with passenger carrying approval. Consequently, the latter was not qualified to act as pilot-in-command for the flight from Ballina to Coffs Harbour. It was not possible to establish who was controlling the aircraft at the time of the accident. Both pilots had limited total flying experience, as well as limited experience on the aircraft type.

The investigation concluded that, following the pull-up from about tree height, the aircraft probably stalled and entered an incipient spin to the right. Recovery from the spin was not effected prior to ground impact. The reason for conducting the pull-up manoeuvre was not determined.

FACTORS

The factors considered relevant to the development of the accident were:

1. The experience level of both pilots was low.

2. Control of the aircraft was lost at a height insufficient to effect a safe recovery.

The aircraft had been stored in a hangar/shed, in a partially dismantled state for about 4 months. The pilot assembled and rigged the aircraft with the help of a person not familiar with aviation, and without reference to any qualified person or documentation. The pilot then boarded the aircraft, started it, and taxied for take-off. The take-off appeared normal, and the aircraft turned 90 degrees to the right at the upwind end of the runway. During the climb, at about 300 feet above ground level, the aircraft was seen to adopt a steep right wing low attitude and enter a spiral descent to ground impact.

The pilot was rescued from the wreckage and taken to the hospital, where he later died. He was not wearing a helmet during the flight.

Inspection of the wreckage revealed a broken wooden plug in the wing warping rod, where it attaches to the forward part of the right wing. The remains of the plug were found partially withdrawn from the rod end and an inspection of the left wing warping rod revealed the wooden plug partially withdrawn from its rod end by an amount similar to that found in the right wing. Microscopic analysis of the broken plug showed that the plug had been broken prior to the ground impact and that its material, which did not meet the manufacturer's specifications, had also degraded after lengthy exposure to the environment.

The plug failure, alone, should not have resulted in the loss of control of the aircraft. The aircraft is controllable with an adjustment of the position of the controls to compensate for the loss of the warping rod.

No other defects were found in the aircraft which could have contributed to the loss of control and subsequent crash.

The pilot's logbook contained no reference to prior experience in flying the Scout aircraft and indicated that he was inexperienced in operating ultralight aircraft. Anecdotal evidence suggested that he had more total hours than recorded in the logbook and also had some flying experience in the Scout, about two years prior to the crash.

The pilot had been solo-checked eight months prior to the crash and his logbook indicated that he had flown, unsupervised, on many occasions since that flight check, in contravention of the Australian Ultralight Federation Operation Manual requirements.

The wind on the ground at the time of the take-off was westerly at about 5 knots and was likely to have been stronger above tree top level. As the pilot turned away from the take-off strip, he probably would have had a tailwind component.

It is probable that the wooden plug broke after take-off. The pilot lost control following the failure, either because of inexperience, or he was distracted by the failure and allowed the speed to decrease to the stall speed as the aircraft climbed. The rudder is normally used for primary roll control of the Scout and if the pilot had not been aware of this, he may have aggravated the situation by using other recovery techniques.

Safety Actions

The Bureau of Air Safety Investigation has made the following recommendations:

1.  That the Civil Aviation Authority, in consultation with the Australian Ultralight Federation;

i) Advise owners of Wheeler "Scout" Mk3 ultralight aircraft to examine the wing warping control attachments and replace any suspect parts, and ii) As a matter of urgency complete and distribute the AUF Technical Manual.

2. That the Civil Aviation Authority research the wearing of helmets in ultralight operations with the view to determining if regulation in this area is warranted.

3. That the Civil Aviation Authority;

i) Examine its procedures for surveillance of sport aviation groups to ensure that the standards required by the regulations are being met;

ii) Actively pursue breaches of regulations or operating procedures, and, in conjunction with the Australian Ultralight Federation,

iii) Maintain an ongoing education programme of all ultralight operators with regard to their privileges and responsibilities under the Civil Aviation Orders and the AUF Operations Manual.

The following Safety Advisory Notices have been sent to the Australian Ultralight Federation:

1. The Australian Ultralight Federation should consider reminding all ultralight operators of;

i) The dangers associated with substituting substandard parts in their aircraft, and, 

ii) The dangers associated with not maintaining their aircraft to manufacturers' specifications.

2. The Australian Ultralight Federation should emphasise the potential safety benefits in wearing helmets during ultralight operations.

The pilot was mustering cattle. The helicopter's gross weight was estimated at 602 kilograms which was 20 kilograms below maximum allowable. The terrain was approximately 1000 feet above sea level and the outside air temperature was about 25 degrees Celsius.

The surviving passenger recalled that the helicopter was about 35 feet above ground level when he first heard the low rotor warning horn and saw a warning light on the instrument panel. There were trees ahead which were about 25 feet high. The pilot said "whoops", pulled up, nosed over and veered slightly left towards a gap in the trees. At the time the helicopter had very little forward airspeed. He subsequently described a weightless feeling which is consistent with the pilot having applied a large forward cyclic input to achieve the "nose over". He recalled that the pilot was "fighting" the cyclic control for a short time as the helicopter rolled to the right into a tree. The survivor also remembers leaves flying about but he has no recollection of a rotor blade hitting a limb.

Damage sustained by the helicopter indicated that the main rotor struck a tree limb and that one rotor blade was severed about one metre inboard from its tip. When the section of rotor was severed, the remaining rotor blade flapped up causing a severe mast bump which resulted in overload failure of the mast at the main rotor head. The main rotor assembly departed and the unsevered rotor blade impacted the first section of the tail boom immediately aft of the engine. The main rotor did not sever the tail boom or the tail rotor drive shaft or the tail rotor control tube. The tail rotor drive shaft within the tail boom was severed in torsional/bending overload when the boom separated probably as the helicopter impacted the tree and fell through its limbs.

The right side of the helicopter, in the area of the fuel tank to the pilot's upright seat cushion, was pushed inwards probably when the helicopter impacted the tree. The right side of the landing skid was severely deformed and broken. No such damage was found on the left skid. It is probable that, after the tree impact, the helicopter impacted the ground right side low and bounced on to its left side where it was found at rest. There was no post crash fire. Damage to the tail rotor assembly indicated that the tail rotor was still rotating but probably not being driven by the engine when the tail rotor blades impacted foliage.

The helicopter was found with both the drive belts off the pulleys associated with the drive system from the engine to the main gearbox. There was no evidence of previous damage or wear on the drive belts, the pulleys or bearings; nor has any fault been found with the clutch or free wheeling unit. However, marks were found on the inside opposing faces of the flexible coupling between the main gearbox output shaft and the tail rotor drive shaft, forward of the upper pulley assembly. This indicates that the upper pulley assembly had moved forward abruptly thereby misaligning the belts enough for them to jump off the pulleys. There is no known inflight manoeuvre which could compress the forward coupling to the extreme as found. However, a severe tree impact or ground impact could dislodge the upper pulley assembly enough to damage the coupling and cause the belts to come off. It is most likely that the drive belts came off after the initial tree strike by the main rotor and not before. Engineers have found no significant fault with the engine or airframe which might have contributed to the accident. A magnetic particle inspection of engine components proved that the engine had not suffered a significant overspeed.

Subsequent trials in a Robinson R22 helicopter were conducted by a very experienced flying instructor in conditions similar to the day of the accident. His helicopter successfully hovered out of ground effect at 35 feet above the ground with rotor revolutions per minute (RPM) as low as 96% at which time the low rotor RPM horn was audible and the low rotor warning light was illuminated. During a simulated engine failure from a low hover it was noted that the cyclic still responded normally with rotor RPM as low as 75%.

The survivor's description of the accident is consistent with the pilot having inadvertently achieved low rotor RPM, possibly losing height, and trying to recover while avoiding nearby trees. His description suggests that the "nosing over/bunting manoeuvre" managed to unload the main rotor to the extent that tail rotor thrust rolled the helicopter to the right. It is a known fact that a pilot may not be able to counteract this uncommanded roll to the right with left cyclic input. It is probable that an uncommanded roll to the right caused the helicopter to collide with a tree; this is consistent with the survivor's description of the helicopter being "pulled into the tree".

SIGNIFICANT FACTORS

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

1. The pilot inadvertently allowed the rotor RPM to decay.

2. During the attempted recovery from low rotor RPM, the pilot's flight control inputs induced an inflight manoeuvre which resulted in an uncommanded roll to the right.

3. The helicopter collided with a tree.