Circumstances:

The aircraft was cruising in clear and smooth conditions, some time after storms had been encountered, when it suddenly pitched upwards. Both the Captain and First Officer manually opposed the pitch up by applying considerable forward pressure to their control columns. The autopilot was disengaged by the Captain and the aircraft was descended to the assigned cruise flight level. During the above manoeuvres, some passengers were injured by contact with the aircraft structure.

A number of these passengers had been unrestrained in their seats, despite instructions that it was a company policy that seated passengers were to have their seat belts fastened. A doctor, who was aboard, assessed that some of the passengers' injuries were sufficiently serious to warrant hospital treatment. The Captain elected to divert to Darwin. Fifty passengers were treated in hospital including ten who were admitted. Analysis of the Digital Flight Data Recorder fitted to the aircraft indicated that during the flight excursion and subsequent recovery the aircraft climbed 1650 feet, the airspeed decreased by 45 knots and it was subjected to maximum and minimum vertical accelerations of +1.9 and -0.3 g. (The normal g force exerted on an object on the earth is +1 g.)

The Captain stated that he initially thought that the aircraft had encountered a meteorological phenomenon known as a standing wave. The preflight meteorology briefing received by the flight crew indicated the possibility of clear air turbulence but did not mention standing waves. However, during the pitch up the Captain realised that there was an autopilot malfunction (there was no warning from the system that the autopilot had malfunctioned). He elected not to disconnect the autopilot immediately because he thought that the removal of a large but unknown nose up force from the control column would lead to excessive negative 'g'.

The autopilot was disengaged after the aircraft returned to a more normal attitude. There was a requirement to reduce the nose up attitude fairly quickly if a 'g' induced stall was to be avoided. The Captain stated that his actions were a compromise between reducing the aircraft's nose up attitude to prevent a stall from developing and keeping negative 'g' to a minimum for passenger safety. The optimum outcome from the autopilot malfunction would have been obtained if it had been initially recognized as such and an early disengagement of the autopilot accomplished.

However, given that clear air turbulence had been forecast and moderate turbulence reports received from two other aircraft, it is not unreasonable that the Captain initially thought that the disturbance to the aircraft flight path was caused by meteorological conditions. Given that the disturbance was originally diagnosed as of meteorological origin, the Captain's actions were logical and the recovery technique from the resultant unusual attitude was correct. Maintenance investigation by the operator disclosed that the aircraft had suffered similar autopilot malfunctions over recent months. The flight crew was not aware of this history. The cause of the malfunction was traced to an intermittent defect in the Air Data Computer system.

Significant Factors:

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

1. There was an intermittent fault in the Air Data Computer system which resulted in the autopilot commanding a sudden pitch up of the aircraft.
2. The flight crew initially misidentified the cause of the pitch up which in turn resulted in a delay in disengaging the malfunctioning autopilot.
3. Some seated passengers were not wearing seat belts despite instructions to do so.

Recommendations:

During the application of negative 'g', several unrestrained passengers collided with overhead lockers/panels and received neck injuries. Similar injuries could be expected during an encounter with turbulence. The first aid kits carried on the aircraft did not include neck braces. Passengers flying on any large aircraft could receive similar injuries. It is recommended that the Aviation Medicine Branch of the Civil Aviation Authority consider a requirement for all Regular Public Transport aircraft first aid kits to be equipped with an appropriate number of neck braces.

Circumstances:

The flight from Mount Isa had been conducted in rain and cloud. At 5000 feet during the descent, the pilot became visual with the runway lights and the nearby goldmine. The runway was overflown, and it was noted that the windsock was showing no significant wind. During the circuit for landing on runway 21, increasing rain and cloud was noticed on downwind, and on left base the pilot experienced heavy rain and strong wind gusts. The pilot had turned the windscreen wipers on, but they were not clearing the windscreen effectively.

Forward visibility was significantly reduced, and on final approach the pilot was having difficulty keeping the aircraft aligned with the runway due to the turbulence and wind gusts. He elected to go around and carry out another circuit. During the next circuit, the conditions had not improved, and the pilot again decided to go around, as it had become increasingly difficult to maintain runway alignment. As the go-around was commenced the pilot heard a loud bang and realised the aircraft had struck trees. The aircraft was climbed and the Kidston NDB approach procedure was carried out.

The pilot became visual at 2900 feet and carried a circuit and landing on runway 03. (Kidston is 1620 feet above sea level). After shutdown, the aircraft was inspected and was found to have sustained tree impact damage to the left inboard leading edge, the left propeller, and the left horizontal stabiliser. The pilot believes the tree strike occurred as a result of downdraft associated with the storms in the immediate area. The Kidston aerodrome is established according to the provisions of AIP AGA-6 and although approved for the night operation being conducted, it does not have an approach guidance lighting system.

The aerodrome does not have any other ground lighting in the immediate vicinity other than the runway lights, and this may lead to the pilot having a false perception of height and runway perspective. It is considered that the lack of approach guidance, combined with the prevailing weather conditions, contributed significantly to the cause of this accident. There is rising terrain on the approaches to runway 21. The pilot reported that he was having difficulty with forward visibility due to the ineffectiveness of the windscreen wipers.

The effect of heavy rain on aircraft windshields may lead to a number of visual errors. One effect is to make objects appear to be lower in relation to the aircraft than they actually are. Whilst it is difficult to estimate the magnitude of the error, the elements were present in this accident and may have given the pilot a false impression of his height in relation to the runway lights.

Significant Factors:

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

1. Weather associated with thunderstorms in the local area.
2. The aerodrome is not equipped with a runway approach lighting system.
3. During a visual approach, the pilot encountered excessive crosswind, reduced visibility, and turbulence.
4. The aircraft struck a tree on the approach to runway 21, due to the inability of the pilot to appreciate the proximity of the aircraft to the terrain on final approach.
5. The aircraft windscreen wipers were not working efficiently.
6. Excessive rain on the windscreen may have caused a visual error and contributed to the pilot flying the aircraft into an undershoot situation.

Recommendations:

During the preliminary stages of the investigation the following recommendation was made to the Civil Aviation Authority: - The Civil Aviation Authority should immediately review the suitability of Kidston aerodrome for night operations. The aerodrome was surveyed in February 1989 preparatory to the installation of approach lighting. The system was installed but was not commissioned due to problems with excessive light intensity. The Civil Aviation Authority should assess the need to make approach guidance lighting a requirement for night operations at Kidston.

Circumstances:

At 0032 hours the pilot advised Flight Service that he was taxiing at Mount Gambier and nominated runway 36 for take-off. A report was received at 0040 hours indicating the aircraft was back-tracking on runway 36. No further reports were received from the aircraft. As a result of transmissions received from an emergency locator beacon, a ground search subsequently located the wreckage of the aircraft in a pine plantation about 480 metres north-west of the northern end of runway 36. Conditions were moonless and very dark, with no fixed ground lighting for 13 kilometres to the north of the aerodrome. As a result, there was probably no visible horizon. There is a high probability that low level cloud layers at about 2000 feet may have been of sufficient thickness and extent to totally obscure any starlight. The wind was from the north-west at 2 knots. The investigation found the aircraft was banked slightly right when it initially struck the tops of tall pine trees about 280 metres beyond, and 170 metres to the left of the extended centreline of runway 36. The aircraft travelled a further 220 metres before striking the ground at an angle of about 40 degrees. Both wings had been torn off prior to ground impact, the landing gear was extended, and propeller damage was consistent with low RPM. Apart from a defect found in the fuel control unit, which may have resulted in engine rough running during power changes, the aircraft was considered to have been airworthy at the time of the accident. The pilot had been awake for almost 18 hours prior to the accident and may have been fatigued. His night flying experience, particularly related to dark night take-offs remote from ground lights, was limited. The circumstances of the accident were consistent with the pilot suffering the effects of somatogravic illusion, a very subtle form of disorientation to which even experienced pilots can fall victim. When a pilot is subjected to climb and forward acceleration at the same time, and deprived of external visual cues, he experiences a strong sensation of a steeper than actual climb. It is this "false climb" illusion which tempts the pilot to lower the nose of the aircraft. This increases the forward acceleration component and increases the illusion of climbing steeply. Owing to lag in the altimeter and vertical speed indicator, the loss of height may go unnoticed until it is too late to avoid collision with the terrain. Somatogravic illusion can be overcome by anticipating and ignoring the illusion, establishing an appropriate climb attitude on the attitude indicator, and confirming that the desired climb speed is achieved and maintained.

Significant Factors:

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

1. Very dark conditions for take-off with no visible horizon.

2. Pilot may have been fatigued.

3. Limited pilot experience in the prevailing conditions.

4. Somatogravic illusion probably encountered by pilot during initial climb

5. Failure to establish appropriate climb attitude by reference to the flight instruments.

Recommendations:

It is recommended that Civil Aviation Authority continues to ensure that pilots are educated about the subtle dangers of the somatogravic illusion, and the procedures to counteract it. In response to this and a similar previous recommendation, the Civil Aviation Authority intends publishing an article on the subject. The Authority is also going to advise the relevant sections of the aviation industry about the illusion.

During the climb at about 120 feet above ground level, the engine stopped suddenly. The student promptly lowered the nose of the aircraft to maintain flying speed. Almost immediately, the instructor took over and increased the nosedown attitude in an attempt to increase the airspeed. However, he had to pull back on the stick almost straight away to attempt a flare for landing. The aircraft had not gained sufficient airspeed to fully respond and mushed into the ground with a heavy impact. The first witness on the scene to render assistance noticed that the ignition " kill " switch was in the OFF position although both pilots were adamant they had not switched it off as a deliberate action after the crash. Subsequent inspection of the engine by a Civil Aviation Authority engineer and a test run of the engine by the company engineer failed to find any reason for the engine failure. Further experimentation, however, showed that the " kill" switch could be placed in a mid-position which would allow the engine to start and then the switch could move to either the ON or OFF position by vibration. Although the actual cause of the engine failure could not be established, it is probable that the ignition " kill " switch was placed in the OFF position inadvertently or vibrated into the OFF position from a mid-selection position.

During the take-off run the pilot sensed a loss of power being transmitted to the propeller. He assessed that he could not stop in the strip length remaining and reduced the throttle setting in the hope that the reduction drive would transmit the reduced power to the propeller. The aircraft cleared the fence at the end of the strip, but the pilot was forced to turn through about 90 degrees to avoid a power line and to line up with the contours of the ploughed field he had selected for a forced landing. During this turn the airspeed reduced to the point where a high sink rate developed, and the pilot had insufficient height or power to effect a recovery before the aircraft mushed into the ground. On impact, the left mainwheel was torn off and the aircraft overturned some five metres beyond the initial touchdown point. Specialist investigation showed that disc springs had been incorrectly replaced during a modification to the reduction gearbox. This allowed the dog gear to ride up and out of the dog hub, under the reduced stiffness of the axial spring assembly, and reduce the transmission of power to the propeller. Investigation also revealed that there was some ambiguity in the assembly instructions for the gearbox modification.

An aircraft cleaner reported finding significant damage to the landing gear and wing spars of the aircraft during a routine cleaning operation on the afternoon of Sunday the 17 October 1988. The damage to the aircraft indicated that the aircraft had probably been stalled at a significant height above the ground descended vertically and touched down heavily on the left wheel followed by the right wheel. Damage to the left wing was readily visible on the upper skin surface. Six pilots had been involved in the operation of the aircraft over the two days preceding the report by the aircraft cleaner. All six indicated that they had not done or had not observed a landing which could have caused the damage found. None of the pilots had observed any damage to the aircraft during their pre or post flight inspections. The damage was such that continued operation of the aircraft could have resulted in a serious air safety occurrence.

Circumstances:

Approaching a reporting point on his cross-country flight the pilot became aware of the failure of a radio navigation aid. Shortly afterwards the pilot was unable to establish radio contact to make his position report. Suspecting an electrical failure but unable to detect the cause the pilot elected to divert to the departure aerodrome. The pilot stated that he turned off all electrically powered services except the VHF radio and was finally able to relay a report through another aircraft. On arrival at Mt Gambier, he made a radio call in the circuit but assumed that the radio was " dead " at that point. Gear was selected DOWN on the downwind leg and the pilot felt that it had extended but reported that he had no gear position indication from the cockpit indicator lights. He then briefly activated the emergency gear extension knob. The pilot continued the circuit for a flapless approach and decided to try and touch the gear on the runway to check if it was extended. A witness on the ground reported seeing the gear extend on the downwind leg and the continuous operation of the aircraft anti-collision beacon. However, when the aircraft was on final approach the witness saw that the main gear was only partly extended, and the nose gear was still in the UP position. His radio calls of warning were not received by the pilot. After a smooth level off for landing the pilot reported feeling the right mainwheel touch down so he reduced power. Almost immediately the gear collapsed, and the pilot was unable to go around from that situation. Subsequent investigation revealed that the source of the electrical failure was a slipping alternator drive belt caused by a worn bracket. The pilot had not flown that type of aircraft for over three months. He was apparently unaware that in order to operate the emergency landing gear system the appropriate knob has to be depressed for about 30 seconds. CAO 40.1.6.1.4.(d) requires the pilot-in command the owner and/or operator of the aircraft to fulfil certain criteria before a proposed flight is undertaken. Evidently none of the parties fulfilled their responsibilities in this regard on this occasion.

Significant Factors:

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

1. Electrical system malfunction caused by slipping alternator belt.

2. The operator did not ensure that the pilot was fully familiar with the aircraft and its systems.

3. The pilot lacked familiarity with the aircraft landing gear system.

4. The pilot did not properly use the emergency gear extension system.

Recommendations:

1. It is recommended that the Civil Aviation Authority emphasise the importance of compliance with CAO 40.1.6.1.4 (d) at Aviation Awareness Seminars.

The pilot was spraying a pea crop in calm conditions. A high voltage powerline was strung above a fence bounding one side of the paddock being treated. The pilot knew of its presence and could see it clearly during the spray runs. At the end of the sixth run prior to making the procedure turn, the pilot felt a slight jolt and was surprised when he saw the powerline collapse. The aircraft's deflector wire contacted the powerline and guided it over the fuselage until it was severed by the deflector wire rear attachment bracket on top of the fin. The pilot advised that he misjudged the clearance between the fence and the powerline and later inspection revealed that the line was hung lower than is usually the case.

On arrival at the destination aerodrome, the pilot was unable to obtain a down and locked indication for the landing gear. He noted that when the gear was selected, there was an abnormal noise, and the gear motor only ran for a few seconds. On a subsequent re-cycling, a down and locked indication was obtained, but the pilot noticed a strong smell of hydraulic fluid. A diversion to a more suitable aerodrome was made, where a flypast confirmed that the gear appeared to be extended. The gear warning horn did not sound when the throttles were closed. However, the pilot was unable to move the emergency gear handle from its stowed position when he decided to use this device to ensure the gear was in fact down. During the ground roll, following a smooth touchdown, the right main gear collapsed. The investigation revealed that the right gear up-lock roller was seized. The pilot did not detect this fault during the pre-flight inspection. The landing gear braze rod, the push rod between the actuator and landing gear, was bent and the relevant gear position microswitch was incorrectly adjusted, resulting in a premature landing gear down and locked indication. The landing gear manual extension handle could not be moved because of an incorrectly fitted trim panel. All these mechanical defects were a consequence of inadequate maintenance.

Prior to his arrival, the pilot had contacted the resort to obtain details on the strip at Arkapena as this was the strip closest to the Wilpena Chalet. Among other details given to the pilot was the information that the strip was used frequently. On arrival, the pilot overflew the strip at circuit height for inspection and then made a full circuit before landing. Touchdown occurred at 170 metres into the strip and at about 245 metres along the strip, the nosewheel entered a washaway. The nosegear collapsed shortly afterwards and the aircraft came to rest on its nose and maingear at about 340 metres from the threshold. The pilot of an aircraft carrying out the recovery and repair to the accident aircraft was briefed by the pilot prior to and on arrival by VHF contact from his aircraft radio. Despite the briefing and warning to the recovery pilot, he was unable to detect any washaways from an inspection at 20 feet above ground level, he subsequently made a safe landing by keeping to the right of the strip centreline as advised by the pilot on the ground.