Circumstances:

The aircraft was engaged in circuit training in the 05 direction. Wind conditions were reported to be 030/5 to 8 knots and gusty. A number of normal take offs and landings were safely executed before the instructor attempted a downwind take-off in the 23 direction. The aircraft was observed to take a longer than normal ground roll. When it reached a height of about 50 feet the left wing dropped, and the aircraft commenced to rotate to the left before striking the ground in a steep nose down attitude on a heading of about 050 degrees. A witness who was standing near the north eastern end of the strip said the wind gusted to about 15 knots from the north east immediately prior to the accident. It would appear that during a critical stage of the take-off, the aircraft stalled after suffering a sudden a loss of airspeed associated with a significant wind shear. This accident highlights the dangers of attempting downwind take-offs in ultra-light aircraft.

Recommendations:

It is recommended the AUF publicise the circumstances of this accident to highlight the dangers associated with downwind take offs in ultra-light aircraft.

The helicopter was tasked to sling load two large metal hooks between two points on a wharf. The first hook was off-loaded, but as the helicopter was lifting the second hook, the tail rotor contacted a solar panel at the top of a light pole. Control of the aircraft was lost and it was observed to perform a nose high turn before striking the water. The helicopter floated inverted and the pilot was able to evacuate himself and swim to a boat. It is considered likely that while concentrating on the position of the load, the pilot diverted his attention from the operation of the helicopter and allowed it to descend, which resulted in the tail rotor strike.

Circumstances:

The pilot had planned to carry out a bore-hole inspection on his property. During the start-up sequence the pilot noted that more choke than normal was required, however, after start-up the engine ran smoothly. Approximately 30 minutes after take-off the pilot observed air bubbles flowing through the transparent fuel line. The engine began to run roughly and stopped. The pilot commenced forced landing procedures and attempted to restart the engine by hand priming the fuel system using the rubber manual priming bulb. The bulb, once compressed, did not return to its original size. The pilot was forced to carry out a forced landing on unsuitable terrain and the aircraft was damaged. The engine fuel pump non-return valve was found jammed in the open position by black rubber particles. These particles had come from the inside wall of the manual priming bulb. An open non-return valve will cause a loss of pressure within the fuel system and engine failure. The fuel tank is mounted well below the engine. Once the particles were removed from the fuel system the engine ran normally. The aircraft's history indicated that it had been left standing in hot and dry conditions for some time allowing the rubber priming bulb to dry out. Manual operation of the dry bulb probably caused internal cracking and allowed rubber particles to contaminate the fuel system.

Significant Factors:

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

1. Deterioration of the rubber manual priming bulb when it was used after having been allowed to dry out over an extended period of time.

2. Contamination of the fuel system by rubber particles from the priming bulb.

3. Interruption to fuel flow and engine stoppage caused by fuel system contamination.

4. Forced landing in unsuitable terrain.

Recommendations:

It is recommended that the Australian Ultralight Federation draw the attention of its members to the possibility that rubber seals and components used in fuel systems, can deteriorate if they are left to dry out. These components, if left for an extended period of time, should be checked for serviceability before they are placed back into use.

The pilot was taking part in an ultralight safari from Boonah to Cloncurry and return. The propeller separated from the aircraft in flight, damaging the tailboom and right wing. The pilot carried out a successful landing on the Warrego Highway. Investigation revealed that the propeller shaft had failed due to a flaw in the metal. This accident was not the subject of an on-site investigation.

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.