Loss of control

Witnesses observed the aircraft at a height of approximately 200 ft soon after take-off from a local grass strip. The aircraft did not gain height and entered a steep nose-high attitude before apparently stalling. The aircraft then pitched down steeply and collided heavily with the ground. The aircraft was subsequently engulfed by fire. The pilot and two passengers sustained fatal injuries.

FACTUAL INFORMATION

History of the flight

The pilot had been tasked to ferry the helicopter from Windorah to Cadelga Station in preparation for cattle mustering. Several witnesses saw the helicopter depart at about 1620 EST. It was last seen some time after 1630 as it flew past South Galway Station, 61 km south-west of Windorah.

The track distance was 239 km with an expected flight time of about 1 hour and 40 minutes and an estimated time of arrival of 1800. The helicopter was expected at Cadelga Station before last light at 1829. When it had not arrived, the helicopter was reported missing. An extensive aerial search commenced at first light the next morning. The wreckage of the helicopter was found about 2 km to the right of the direct track and 31 km short of the destination.

Pilot information

The pilot was 20 years of age and had commenced his flying training on Bell 47 helicopters in March 1995. He gained an endorsement on Robinson R22 helicopters in May 1995. He passed his commercial helicopter licence test on 22 June 1995. In February 1996, the pilot passed a check flight with an instructor and obtained mustering training. Since then, he had been employed as a mustering pilot on a full-time basis.

The post-mortem examination report did not reveal any pre-existing physiological problems.

Wreckage examination

The helicopter wreckage was examined initially at the accident site and later transported to a maintenance facility at Archerfield Airport where a more detailed examination was possible. These examinations revealed that the helicopter had impacted in an attitude about 60 degrees nose-low and banked to the right. The skid gear had separated at impact and the remaining structure of the helicopter was severely compressed.

Significantly, the main rotor had ceased rotating, and the engine had stopped by the time the helicopter struck the ground. Sections of the tail boom were scattered to the right of the main wreckage. Heavy items, such as a jerry can full of oil and the tail rotor assembly, were strewn ahead, along track (approximately 245 degrees M). Lighter items, such as paint flakes and Perspex pieces, were scattered downwind, generally to the north of the main wreckage.

Examination of the main rotor blades found that both pitch-link rods were broken in overload and that both blades were bent into an "S" shape. The tail boom had suffered several main rotor blade strikes. The first blade struck on the flat with the top surface, distorting the tail boom and swinging the tail rotor assembly into the main rotor disc.  The cabin was also struck by one or both main rotor blades.

The engine was bulk stripped at an engineering workshop. Nothing was found that would have prevented the normal operation of the engine. Examination of the exhaust manifold showed that the engine was still hot at impact. Both fuel tanks were holed, subsequently only a small quantity of clean fuel was recovered. The helicopter had undergone a periodic maintenance inspection prior to the flight.

Examination of the helicopter wreckage and of the maintenance documentation did not reveal any abnormalities which could have led to a loss of control.

Weather and environmental issues

An assessment of the weather conditions was obtained from the Bureau of Meteorology and local sources. The wind at 2,000 ft was a southerly at 10-15 kts. The surface wind was a light south-south-easterly, less than 5 kts. Cloud was scattered cumulus at 3,000-4,000 ft with patches of higher altocumulus. Sunset at the crash site was at 1808.

Robinson Helicopter Company research

Research undertaken by the Robinson Helicopter Company found that when the main rotor RPM decreases below 75% RPM, it will continue to decrease regardless of input from the pilot. In a short time span, the engine will stall, and the rotor system will stop completely. During flight with rotor RPM in the normal range, the blades are relatively straight due to centrifugal force. As rotor RPM decreases below the normal range, the main rotor blades bend upwards in a permanent set, the pitch link rods break in overload and the droop stop tusks also break or bend. The main rotor blades are then free to swivel at the mast and flail, striking the tail and cabin structure.

Cabin luggage

Any luggage has to be carried in the cabin of the helicopter: in the space under each seat, on the passenger's seat, or on the cabin floor in front of the passenger's seat.

The pilot carried three bulky items in the cabin: a swag (bedroll), a full 20-L jerry can, and a small overnight bag. The rolled-up swag was later measured at 1,060 mm long by 350 mm in diameter. It was held upright by the lap/sash seat belt on the passenger's seat. The location in the cabin of the 540 x 300 x 200mm overnight bag could not be determined. The jerry can containing engine oil was ejected from the helicopter, indicating that it was not restrained and probably lying on the cabin floor in front of the passenger's seat.

The swag and overnight bag were removed from the wreckage before the investigation team arrived on site. Therefore, any evidence of control interference caused by the luggage was lost. The Bureau's records show that since 1989 there have been four other similar occurrences, three of which resulted in accidents. In each occurrence, control was lost either totally or partially, due to inadequately restrained cargo in the cockpit. The 1989 accident was due to the in-flight movement of a swag and other equipment, held only by the passenger's seat belt.

Emergency locator transmitter

An emergency locator transmitter was not fitted to the helicopter, nor was one carried by the pilot.

ANALYSIS

Loss of control

The loss of main rotor RPM and engine stoppage was preceded by an event which resulted in loss of control. This event was sudden and severe enough to prevent the pilot from taking timely corrective action. An assessment of the helicopter's attitude at impact and the wreckage distribution indicated that this event occurred at an altitude in excess of 500 ft.

There was no physical evidence found to indicate that the swag shifted and interfered with the flight controls.

The event which led to a loss of control could not be identified.

SAFETY ACTION

Since 1989 there have been four similar occurrences, three of which resulted in accidents. In each occurrence, control was lost either totally or partially, due to inadequately restrained cargo in the cockpit.

The Bureau of Air Safety Investigation is considering an article for publication in Asia-Pacific AIR SAFETY highlighting the risks to safety from carriage of cargo in the cockpit of the Robinson R22 helicopter.

At a result of the investigation into this occurrence, the Bureau of Air Safety Investigation forwarded the following interim recommendation to the Civil Aviation Safety Authority on 4 November 1996:

IR960127

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

1. review the Aviation Safety Surveillance Program to ensure that new commercial operators are adequately monitored and inspected until a demonstrated history of safe operation is known;
2. align the scheduled surveillance period of the Aviation Safety Surveillance Program to that of the validity period of the air operators certificate;
3. reconsider the flight review requirements for Chief Pilots with the view of bringing them into line with the current situation for Chief Flying Instructors, as an additional method of surveillance;
4. review the adequacy of the approval and assessment requirements for Chief Pilots who do not have a demonstrated history in flight operations with a commercial operator;
5. review the current situation regarding Aeroplane Flight Reviews, to allow for appropriate notification to the Civil Aviation Safety Authority and recording of the results.'

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".

The aircraft was being operated on a flight over the pilot's property to inspect bores. It had been airborne for about 90 minutes.

The pilot contacted his son, who was mustering sheep on the property, on a hand-held radio to advise that he was returning to the station airstrip to refuel.

About three minutes later the crashed aircraft was observed by the pilot's son who had not seen or heard the aircraft immediately before the accident. The aircraft had impacted the ground in a near-vertical nose-down attitude and the pattern of damage to the left wing indicated that the aircraft had been rotating to the left when it struck the ground.

The pilot, the sole occupant, had sustained fatal injuries.

An inspection of the aircraft did not reveal any evidence of pre-impact defects. The engine was running at impact; some flap was extended and there was evidence of post-impact fuel leakage.

The pilot had completed a biennial flight review (BFR) in December 1994 and was correctly licensed to carry out an aerial inspection flight.

The nature of the impact indicates that the pilot lost control of the aircraft and was unable to regain control prior to impact with the ground.

The reason for the apparent loss of control was not determined.

Sequence of events

On the morning of 8 April, the pilot flew the aircraft from Archerfield to Gatton to practise aerobatics. That afternoon he carried out two flights during which he performed an aerobatic sequence known as a "free program", which is a sequence of manoeuvres designed by the pilot to meet certain criteria. The following morning, the pilot carried out a check flight with an instructor to obtain approval in accordance with Civil Aviation Regulation 155(3), to conduct aerobatics down to a minimum height of 1,500 ft above ground level. The minimum height for aerobatics is 3,000 ft above ground level unless this approval is obtained.

Early in the afternoon, the pilot commenced a flight to practise his "free program" again. The flight was observed from the ground by other pilots, one of whom was in radio communication with the pilot. On this occasion it was planned to critique the flight via the radio. The pilot on the ground, who was an experienced aerobatic pilot, stated that about halfway through the sequence he could see there was a problem. The aircraft had been inverted for 5 or 6 seconds after a half loop, before performing a half loop downwards and returning to upright flight. The observing pilot said that after reaching a horizontal attitude, the nose of the aircraft pitched up 40-60 degrees and the aircraft rolled to the right. He immediately queried the pilot as to what he was doing but received no response. The aircraft continued rolling slowly to the right and several more transmissions were made, but there was still no response. The aircraft then appeared to stabilise, and the pilot responded saying that he thought he might have blacked out, but that he was all right now. He then said that he thought he would land and have a rest for a while.

The landing appeared to be normal, and shortly afterwards the events of the flight were discussed with the pilot. The pilot said that he could remember the nose of the aircraft coming up to the horizon, but he did not remember anything after that until the aircraft was near the downwind leg of the circuit. A discussion was held on "G-LOC" (g-induced loss of consciousness) and its possible effects including disorientation. After further discussion the pilot decided that he would make another flight later that afternoon, as he did not appear to have suffered any aftereffects. A technique was then discussed which would reduce the g force during the manoeuvre and help prevent the situation from recurring during the sequence.

At about 1730 EST, the pilot took off to practice the "free program" sequence again. He was in radio communication with his brother, a highly experienced pilot and flying instructor. The pilot had said that he would increase the base height for the sequence as an added safety margin.  The sequence was commenced and proceeded normally and the manoeuvre which had previously caused the problem was performed with what appeared to be the suggested modifications. However, shortly after recovery to the straight and level attitude from the downward half-loop, the nose of the aircraft pitched rapidly to 10 degrees nose-up and the aircraft began to diverge slowly to the right with the nose continuing to rise slowly. The aircraft then commenced a continuous roll to the left. During this time, the ground observer made several unsuccessful attempts to contact the pilot by radio. The nose of the aircraft dropped, and the aircraft dived almost vertically into the ground from a height estimated by witnesses as 2,000-2,500 ft.

Wreckage examination

Examination of the wreckage did not reveal any defects or failures which may have been present before impact, and which could have contributed to the development of the accident.

The canopy had been previously broken when a radio detached from its mounting in the rear cockpit during aerobatics. Two parallel cracks extended laterally across the top of the canopy over the rear cockpit. A repair had been carried out by stitching the cracks with locking wire. The impact site and wreckage did not initially yield a representative quantity of Perspex (only about 20 per cent was found) and the site was then excavated.

Approximately 60 per cent by weight of the canopy Perspex was recovered from the impact crater, including the lockwire stitching with some Perspex still attached. The remainder of the canopy Perspex probably broke into fragments smaller than those recovered. A thorough ground and air search was carried out for Perspex under the flight path, but none was found. This evidence indicates that the canopy is unlikely to have failed in flight.

Impact information

Microscopic examination of both airspeed indicator faces revealed a pointer impact indicating 195 kts on one instrument. The aircraft impacted the ground vertically making a crater approximately 1.3 m deep. The impact forces were not survivable.

Medical

The pilot was assessed as medically fit for issue of a Class 2 medical certificate in December 1994 and appeared to be in good health on the day of the accident. Pathological examination showed evidence of coronary artery stenosis which could have affected the pilots g tolerance. However, medical opinion was that this could not be categorically stated to be the cause of a low g tolerance, or a contributing factor to the accident.

Research and analysis

From the available evidence it appears that the fatal flight was a repeat of the previous flight, except that on this occasion the pilot was unable to regain consciousness before the aircraft struck the ground. The aerobatic sequence up until the time of control loss was, in the opinion of witnesses, flown with more precision and was of a higher standard than on the previous flight. The manoeuvres were described as being tighter, and the pilot was probably generating more g than on the previous flight. He had been advised to reduce power during the manoeuvre that had previously caused the symptoms consistent with G-LOC, to enable the downward portion of the manoeuvre to be conducted at a slower speed and therefore reduced g. Witnesses said that a power reduction was heard during the inverted part of the manoeuvre, but the entry speed is not known.

A BASI Air Safety Research Report produced in February 1988, "The possibility of G-Induced loss of consciousness (G-LOC) during aerobatics in a light aircraft", stated that with sustained moderate rates of onset of g force, G-LOC is preceded by visual symptoms such as grey-out and then black-out (loss of vision). G-LOC is due to the reduced flow of blood to the brain when the magnitude of g in the vertical axis (Gz) passes beyond a particular value, the G-LOC threshold. Beyond this value, neurones fail to function in the absence of the oxygen replenishment provided by the normal blood flow and G-LOC occurs.

The report stated that with a rapid g onset (1g per second for more than 3 to 5 seconds) sudden loss of consciousness may occur without the prior visual warning symptoms. High performance aerobatic aircraft such as the Pitts S2 are quite capable of achieving rapid g applications, and rapid g onset is frequently experienced by competitive aerobatic pilots.

Centrifuge research has shown that there is a period of functional incapacitation following G-LOC lasting an average of 15 seconds. Full recovery may take 30 seconds or longer from the initiation of the manoeuvre that induces G-LOC. An aircraft descending vertically at an average speed of 120 kts will take approximately 15 seconds to reach the ground from 3,000 feet.

Gz tolerance is reduced by various factors such as fatigue, hypotension (low blood pressure), hypoglycaemia (low blood sugar), dehydration, and illness. The pilot was, by all accounts, in good health at the time of the accident, but it is not known what factors may have affected his g tolerance.

Conclusion

Findings

1. The pilot was correctly licenced and endorsed to carry out the flight.
2. The pilot probably experienced G-LOC on the flight previous to the accident flight and was subsequently advised on a means of avoiding a recurrence.
3. The accident flight was commenced some hours later for the purpose of the pilot practising the same manoeuvres as on the previous flight.
4. The aircraft was seen to go out of control at the same part of the sequence as on the previous flight.
5. The pilot did not answer repeated radio transmissions after the aircraft had gone out of control.
6. The pilot had a medical condition which may have reduced his tolerance to g.
7. There were no mechanical defects found which may have contributed to the development of the accident.

Significant factors

1. For reasons which could not be positively determined, but probably related to G-LOC, the pilot lost control of the aircraft.
2. The pilot did not regain control of the aircraft before it struck the ground.

FACTUAL INFORMATION

History of the flight

Pylon racing was conducted at Valley Field, south of Launceston, from 14-19 February 1995. Following completion of the races five T-28 aircraft were to be flown back to the mainland from Launceston. The plan was for the T-28s and a PA-31 to return to the mainland in loose formation.   The role of the PA 31 was to provide search-and-rescue support in the event of a T-28 ditching.  On the morning of the accident the formation leader briefed the pilots involved.  Take-off was to be in formation pairs, spaced a short time interval apart.  The first two pairs were to be T-28 aircraft.  The pilot of VH-LAO asked to be in the last pair which meant flying in formation with the accompanying PA-31 aircraft.  The flight was briefed as a normal departure, no mention was made of the performance of any aerobatic manoeuvres, nor did the pilot of VH-LAO discuss this possibility with any of the other formation members.

The formation take-off on runway 32 proceeded as planned with the pairs taking off at 15-20 second intervals.  Due to the performance of the PA-31 being lower than the T-28, the climb speed of the last pair was limited to about 120 knots.  Observers reported that the third pair made a normal take-off and initial climb, with the T-28 to the left of the PA-31.  At a height of about 500-600 feet the nose of VH-LAO was seen to rise and the aircraft started rolling to the left.  The left roll continued with altitude remaining about the same until the aircraft had rolled inverted. At about that stage of the roll, the nose started to drop.  After about 270 degrees of roll, the aircraft's attitude was very nose-low, and the rate of roll had decreased.  Observers indicated the pilot appeared to be trying to recover from the dive, but there was insufficient altitude to regain level flight before the aircraft, still 10-15 degrees nose-down, struck the ground.  Some witnesses thought the engine continued to operate at about the same power as at the start of the manoeuvre, but one person indicated the power was cut while on the final descent.

Damage to aircraft

The aircraft was severely damaged by impact forces and a post-impact fire.

Wreckage trail/wreckage examination

The aircraft struck the ground approximately 100 metres to the left of the extended runway centreline.  The wreckage trail, which extended for about 140 metres, was towards the north-east (about 90 degrees to the right of the take-off path).  The landing gear and flaps were in the retracted position. Examination of the wreckage did not identify any evidence of a pre-impact defect that could have affected the safe operation of the aircraft.  Also, nothing was found that could have caused an uncommanded roll to the left.

Weight and balance

At the time of take-off, the aircraft was loaded to approximately the maximum permissible take-off weight.  Balance was within limits.

Passenger background

The passenger did not have any pilot qualifications.

Pilot history

During 1986 the pilot had completed part of an RAAF pilot course.  He was suspended from this course following unapproved low flying manoeuvres.  Subsequently he took up civilian flying.  At the time of the crash, he held a Grade One fixed wing instructor rating.  In October 1989 he had received an endorsement to conduct basic aerobatic manoeuvres.  At about the same time he also received an endorsement authorising him to teach basic aerobatic manoeuvres, including loops, aileron rolls, slow rolls and barrel rolls.

After obtaining his aerobatic approvals, his logbook showed he had done only a moderate amount of basic aerobatic flying and aerobatic instruction.  Most of this was in simple general aviation type aircraft such as the Cessna 150. These types are small and light and have a very moderate performance compared to the much heavier, higher powered and faster T-28. The pilot did not hold an approval to conduct aerobatic manoeuvres below 3,000 feet.

Reports indicated that during his time as an instructor he had occasionally been involved in abnormal flight activities.  These included continuing flight into poor weather conditions and making multiple very low passes over a country airstrip.  On two separate occasions with student pilots, he had taken the controls and conducted a 360-degree roll manoeuvre.  The aircraft type on which these manoeuvres were flown was not approved to perform aerobatic manoeuvres.  For approximately the last two years the pilot had been employed as a co-pilot on regular public transport operations, but he still maintained an active interest in private flying.

The pilot obtained a T-28 endorsement on 2 April 1994.  During the endorsement he carried out two or three horizontal roll manoeuvres. These were executed from an entry speed of 180 knots, the normal speed for entering such rolls.  A few days later a flight included horizontal roll manoeuvres, using entry speeds of about 190 knots. The pilot did not fly the T-28 again until 12 February 1995, when he did a short flight with the owner of another T-28.  On 15 February he was permitted to fly this T-28 to Launceston with the owner-pilot on board.

At Valley Field the pilot received a low-level check required by the organisers for participants in pylon races.  This check was only for pylon racing and did not include any aerobatic manoeuvres. While at Valley Field, he was trained to fly the pace plane used to start aircraft in the T-28 pylon races. The pilot did not fly in pylon race events but did fly the pace plane on four or five occasions.  The pace plane leads the competitors to the start line and then pulls up out of the way.

The pylon races were conducted at a minimum height of 200 feet, but competitors were permitted to descend to 100 feet on the straight leg.  The races ended on the straight, at which stage the aircraft were at relatively high speeds. At the end of the race a pull up/climb manoeuvre was required, to a height of 2,000 feet.  While doing this pull up/climb, some competitors executed a 360-degree roll manoeuvre.

On one occasion at Valley Field the pilot, while flying a T-28, was observed to carry out a barrel roll aerobatic manoeuvre at a height of about 1,500 feet.  On the day prior to the accident, he flew as a passenger-observer in a T-28 flown by a well-known American air-show pilot, who conducted an impressive low-level aerobatic display.

Medical information

The pilot passed his last pilot licence medical examination on 18 April 1994.  Following the accident a post-mortem examination was performed on both the pilot and the passenger.  No evidence was found to indicate that either the pilot or the passenger had any medical condition that might have contributed to the accident.

Meteorological information

Information from the Bureau of Meteorology indicated that at about the time of the accident the weather was fine. The temperature was about 19 degrees, the surface wind was from 270 degrees at three knots and there were five octas of cumulus cloud with a base of 3,500 feet.  There was no significant turbulence.

Wake turbulence

The only possibility of wake turbulence would have been from the preceding T-28 aircraft, but this could not have caused the manoeuvre flown.

Survival aspects

The accident was not survivable.

Tests

The normal entry speed for roll manoeuvres in the T-28 was about 180 knots.  The speed at the time of the roll that preceded the accident was probably about 120 knots.  Information was sought on the roll capability at the slower speed, and limited testing was done by an experienced competition aerobatic pilot who also owned a T-28.  The aircraft was loaded to a similar weight.  Tests showed that an aileron roll could be completed without losing significant altitude.

Barrel rolls to the left were attempted but in every case the recovery occurred with a 60-70 degree deviation to the right.  The testing pilot used different methods of entry for these manoeuvres.   Significant altitude losses could not be avoided and were approximately 600-800 feet.  On one of the rolls the throttle was closed about two-thirds of the way through the roll. This resulted in an additional altitude loss of about 200 feet.

ANALYSIS

The weather conditions were good.  The only wake turbulence that could possibly have been encountered was from preceding aircraft, which were of the same type.  This could not have caused an upset of this magnitude.  No evidence was found to suggest any abnormality existed with the aircraft.  There was no evidence to suggest that anyone, apart from the pilot, had any idea that an aerobatic manoeuvre might be conducted after take-off.

Evidence indicated that on occasions the pilot had carried out unapproved flying activities. The information indicated a strong probability that on the accident flight the pilot had attempted to carry out a low altitude roll manoeuvre.  He was not approved to do low-level aerobatics, and his background training did not prepare him for such manoeuvres.  He had little experience on the T-28, which is a large, heavy, high powered, single engine aircraft type.  From the evidence, it appears that the pilot was attempting a roll manoeuvre and mishandled the aircraft.  The high degree of hazard associated with attempting such a manoeuvre at such a low height was significantly increased by the relatively low airspeed at which it was started.

CONCLUSIONS

Findings

1. The pilot was correctly licensed and endorsed to fly the T-28.
2. The pilot held an aerobatic endorsement but did not hold an approval to conduct aerobatic manouevres below3,000 feet.
3. The pilot had a moderate level of basic aerobatic experience and had little aerobatic experience on the T-28.
4. The weather conditions were good and did not contribute to the accident.
5. There was no evidence of any defect in the aircraft.
6. There was no evidence to show that anyone apart from the pilot had any idea that an aerobatic manoeuvre would be performed after take-off.
7. The evidence indicated that the manoeuvre carried out was intentionally initiated by the pilot.
8. The relatively low airspeed at the start of the manoeuvre was well below that recommended for the conduct of horizontal rolls.

Significant Factors

1. The pilot had limited experience on the aircraft type and had never been trained for, or approved to do, low-level aerobatic flight on any type.
2. The pilot probably attempted to carry out an aerobatic manoeuvre at an unsafe height.

The aircraft was operating from an agricultural airstrip 600 ft above mean sea level, spreading superphosphate over moderately steep undulating terrain. The duration of each flight was 6-7 minutes. The accident flight was the seventh and probably intended to be the last for the day.

A witness, who was situated under the flight path, reported that the aircraft was tracking east-north-east in what appeared to be normal flight. Her attention was distracted for a few moments and when she next saw the aircraft it was in a near vertical dive with the upper surface of the wings facing her. The aircraft then struck the hillside and burst into flames.

Examination of the wreckage did not reveal any pre-existing defect which may have contributed to the accident. Impact marks on the propeller indicated that the engine was operating at impact.

The superphosphate load remained in the hopper and the emergency dump system actuating lever was in the closed position. Inspection indicated that the dump system was serviceable prior to impact.

Calculations indicated that at the time of the accident the aircraft, although heavily loaded, was operating within the flight manual maximum weight limitation.

A light north-easterly wind was observed at the airstrip. However, at the accident site, which was about 250 ft higher, the wind was a moderate west-north-westerly. Sky conditions were clear with a visibility of 30 km.

The aircraft probably experienced windshear and turbulence as it encountered a quartering tailwind approaching the ridgeline. The result would have been a reduction in climb performance, and it is likely that the pilot attempted to turn the aircraft away from the rising terrain. During the turn it appears that the aircraft stalled and that the pilot was unable to regain control before it struck the ground.

The reason the pilot did not dump the load when the climb performance was reduced could not be determined.

Significant factors

The following factors were determined to have contributed to the accident.

1. Shifting wind conditions conducive to windshear and turbulence were present in the area.

2. The aircraft was climbing at near to maximum allowable weight.

3. Control of the aircraft was lost with insufficient height available to effect a recovery.

FACTUAL INFORMATION

History of the Flight

The pilot had carried out a local flight with his wife, and a number of circuits and landings were made at the property airstrip. His wife then alighted from the aircraft and went inside the residence which was adjacent to the runway. The pilot had said he intended to do a few more circuits and landings. The aircraft was heard taking off a few minutes later, and witnesses located to the south of the strip saw it making what appeared to be a "flat" left turn onto a northerly heading. The witnesses said the aircraft was about 100 m above ground level and that the engine noise level was low. The aircraft then went out of their field of view. A short time later, the crashed aircraft was discovered by a neighbour who was driving towards the property. The weather was fine and there was a light southerly wind at the time.

Impact Information

The aircraft impacted flat ground whilst upright, descending, and slightly left-wing low. It then bounced beneath powerlines which were approximately 11 m high, and across a road in a direction of 315 degrees. The canopy, ailerons, and various small pieces of aircraft separated before the aircraft came to rest upright, 52 m from the initial impact point. There was no fire. The point of impact was about 300 m to the north of the airstrip which is aligned northeast-southwest.

Wreckage Examination

Detailed technical examination of the aircraft was carried out. Specialist examination of a portion of the exhaust pipe confirmed that the engine had been operating at the time of the accident, albeit at low power, as evidenced by the nature of damage to the propeller and the spinner. There were no mechanical defects found that would have prevented the engine from operating normally.

The structure of the aircraft was examined, and no pre-existing structural defects were found. However, a fibreglass fairing from the base of the tailfin had become detached in such a way that it could have restricted the movement of the elevator control surface. Two small screws had pulled out of the lower rear edge of the fairing. A white paint witness mark on the fairing matched the top inboard edge of the left elevator and showed that the two surfaces had at some stage been in contact. When the fairing was placed against the elevator with the witness marks aligned, it was evident that the detached section of fairing could restrict the upward movement of the elevator. In addition, the elevator trim tab was found in the fully down position.

ANALYSIS

The available evidence does not support pilot incapacitation being a factor in this accident.

Examination of the aircraft indicated that it was capable of operating normally at the time of impact. However, there is a possibility that a fibreglass fairing had detached in flight and restricted up movement of the elevators. The elevator trim tab appears to have been fully down at the time of impact, as it had punctured the rudder surface in that position. This trim-tab position is that which normally gives full nose-up trim. However, if the elevator were restricted in upwards movement and only the tab was movable, then downwards movement of the tab would result in a nose-down effect, the reverse of that expected by the pilot.

A control working in the opposite sense to that expected would be extremely confusing to the pilot. A pilot placed in this situation might reduce the power, because the effect of controls is influenced by power and airspeed. The witnesses who saw the aircraft said it seemed to be making very little noise and was flying slow and at a low altitude. The effect of reducing power, however, would be for the aircraft to adopt a nose-down attitude, compounding the difficulty faced by the pilot.

The pilot was possibly attempting to fly the aircraft back onto the airstrip. From the position of the aircraft before ground impact, and in relation to the airstrip, the pilot would have had to make a left descending turn to align the aircraft with the strip. At this point it would have also been necessary to make a power reduction. This would have further compounded the nose-down tendency of the aircraft which the pilot would have instinctively tried to overcome with the use of nose up trim, further exacerbating the nose-down tendency.

While the above hypothesis offers an explanation for the circumstances of the accident, it relies on an assumption that the fibreglass fairing became detached before impact. However, it has not been possible to determine conclusively whether the fairing became detached before or after impact.

CONCLUSIONS

Findings

1. There was no evidence to support pilot incapacitation being a factor in this accident.
2. The aircraft was operating normally on the flight preceding the accident flight.
3. The weather was fine.
4. The aircraft was seen operating at a low altitude with low power setting immediately before the time of the accident.
5. The engine was capable of normal operation but was delivering low power at the time of impact.
6. The nature of the ground impact indicates that the pilot lost control of the aircraft.
7. The elevator trim tab was in the fully down position at the time of impact.
8. The tailfin fairing was detached and showed evidence of having been in contact with the left elevator control.
9. It could not be determined if the fairing became detached before or as a result of the impact.

Significant Factors

1. Control of the aircraft was lost at low altitude for reasons which could not be determined.
2. The pilot was unable to prevent ground impact.

The pilot was scheduled to spray 50 acres of rice with Londax. The paddock was level and open with no significant obstructions.

The aircraft departed Wakool with a fuel quantity of 200 L (144 kg) of AVGAS and approximately 510 kg of a mixture of Londax and water in the spray hopper.

About five minutes before arriving overhead the treatment area, the pilot established radio contact with the farmer, who was to act as the swath marker. After completing the first spray run in a northerly direction, a second run was completed in a southerly direction. During this run the marker observed that the spray equipment was operating. The aircraft departed the area, heading approximately towards Wakool, however, the pilot did not advise the marker of any reason for departing. When unable to re-establish radio contact, the marker arranged for the operator at Wakool to be advised.

The operator's chief pilot commenced an airborne search from Wakool to the paddock where the aircraft had been spraying.  Finding nothing, he returned to Wakool and arranged for the police to be advised that the aircraft was missing, before re-commencing the air search.  He found the wreckage near the base of trees about 2 km south-east of the spray site, close to a private airstrip.  This strip, aligned 080/260 degrees, was about 850 m long and suitable for a Pawnee Brave landing.

The accident site was in trees about 100 m east and about 50 m south of the unmarked 260 degree strip threshold.

At the time of the accident, the temperature was about 20 degrees Celsius.  The weather was fine with a north-north-easterly wind of 5 to 10 kts.  There were no significant gusts, no significant cloud and visibility was excellent.

The aircraft was within its approved centre of gravity and gross weight limits at the time of the accident and the fuel on board was adequate for the flight.

The pilot was appropriately endorsed on the Pawnee Brave, however, he was relatively inexperienced in agricultural operations.  His Grade 2 Agricultural Rating was issued on 5 July 1994, and he completed 10 hours under direct supervision on 28 October 1994, and then a further 8 hours unsupervised prior to accident.

There were no known witnesses to the accident.  Examination of the impact marks on the trees, fence and the ground indicated that the aircraft had struck the trees while tracking 230 degrees, displaced to the south of the extended strip centreline, with an angle of bank of about 110 degrees to the right and an attitude of 30 degrees nose down.  The short distance of about 20 m from the initial impact point to the final resting position of the wreckage was indicative of a relatively slow horizontal velocity.  Damage to the propeller was consistent with the engine producing power at impact. Flaps were ascertained to have been at 15 degrees which was the recommended landing setting for a heavily loaded Pawnee Brave. There was no fire.

The wreckage was examined by engineers at the accident site and the engine and propeller assemblies were later subjected to more detailed inspection.  No pre-existing faults were found with the aircraft which may have contributed to the accident.

The aircraft was not equipped with a survival beacon.

It is possible that the pilot was intending to land into the west on the airstrip near which he crashed.  The approach path for a landing to the west was over open, flat, dry pasture clear of obstacles.  However, on the southern side of the approach path a tree line converged towards the airfield's southern boundary.

Given the impact position in relation to the airstrip, it is possible that the pilot conducted a low-level right turn onto final for a downwind landing into the west and that the aircraft stalled at a height from which recovery was not possible before ground impact.

Significant Factors

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

1.   The pilot probably underestimated the effect of the tailwind component during the turn onto final.