The flight had been arranged to transport a critically injured patient to hospital in Brisbane. The pilot evidently experienced some difficulty in starting one of the engines. However, witnesses reported that the engines sounded normal as the aircraft commenced moving from the parking area. At 0310 hours the pilot contacted Brisbane Flight Service Unit and reported that the aircraft was taxying. He advised that he was in a hurry, and indicated that he would provide details of the flight after takeoff. Two minutes later he advised that takeoff was being commenced from Runway 14. No further transmissions were received from the aircraft. The aircraft was seen to become airborne and shortly afterwards enter a fog bank. Other witnesses subsequently reported hearing the sounds of an impact. The investigation revealed that the aircraft had collided with a tree 800 metres beyond the aerodrome boundary, while tracking about 10 degrees to the right of the extended centreline of the runway. It had then continued on the same heading until striking the ground 177 metres beyond the initial impact point. The wreckage was almost totally consumed by fire. The extensive fire damage hampered the investigation of the accident. The surviving passenger believed that the aircraft was on fire before the collision with the tree. No other evidence of an in-flight fire could be obtained, and it was considered possible that the survivor's recall of the accident sequence had been affected by the impact and the fire. Such discrepancies in recall are not uncommon among accident survivors. The elevator trim control jack was found to be in the full nose-down position, but it was not possible to establish whether the trim was in this position prior to impact. Such a pre-impact position could indicate either a runaway electric trim situation or that, in his hurry to depart, the pilot had not correctly set the trim for takeoff. The aircraft was known to have had an intermittent fault in the engine fire warning system. The fault apparently caused the fire warning light to illuminate, and the fire bell to sound, usually just after the aircraft became airborne. The pilot was aware of this fault. It was considered possible that, if the fault occurred on this occasion as the aircraft entered the fog shortly after liftoff, the pilot's attention may have been focussed temporarily on the task of cancelling the warnings. During this time he would not have been monitoring the primary flight attitude indicator, and would have had no external visual references. It was also possible that, if for some reason the pilot was not monitoring his flight instruments as the aircraft entered the fog, he suffered a form of spatial disorientation known as the somatogravic illusion. This illusion has been identified as a major factor in many similar accidents following night takeoffs. As an aircraft accelerates, the combination of the forces of acceleration and gravity induce a sensation that the aircraft is pitching nose-up. The typical reaction of the pilot is to counter this apparent pitch by gently applying forward elevator control, which can result in the aircraft descending into the ground. In this particular case, the pilot would probably have been more susceptible to disorientating effects, because he was suffering from a bronchial or influenzal infection. Although all of the above were possible explanations for the accident, there was insufficient evidence available to form a firm conclusion. The precise cause of the accident remains undetermined. POSSIBLE

Circumstances:

The aircraft landed at Sydney to refuel after an uneventful flight from Hobart. After landing it was found that maintenance was required to rectify a flat battery. Subsequently, the aircraft was refuelled on a concrete apron adjacent to the maintenance hangar. In order to prevent fuel venting, the pilot had instructed the refuellers not to completely fill the right inner tank. Fuel was later observed leaking from the aircraft centre section on completion of the refuelling. The leak diminished when the refuellers had about 10 L of fuel syphoned from the right inner tank. Fuel was observed to drain from both engine nacelles and pool on the apron whilst the pilot was preparing to start the engines. The flow diminished when the fuel mixture controls were selected to the cut-off position. The pilot decided to start the left engine after an attempt to start the right engine was unsuccessful. Immediately after the engine fired, there was a violent explosion in the underfloor area, igniting the fuel which lay beneath the aircraft. Flames entered the cockpit through the damaged floor, causing minor fire damage before aircraft engineers extinguished the fire with portable extinguishers. Although injured, the occupants were able to vacate the aircraft without outside assistance. An investigation revealed a significant pre-existing fuel leak from the right inner fuel tank. The leak resulted from deterioration of the top rear seam of the fuel bladder. As the fuel tank compartment was not fitted with a discrete fuel drain, fuel leaking from the bladder flowed along the inner skin of the wing and entered the underfloor area of the fuselage. The aircraft had been inspected for the re-issue of a Certificate of Airworthiness three months prior to the accident. That inspection had failed to detect the deterioration of the right inner fuel tank. Fuel loss had been observed after previous refuellings but was assumed to have emanated from the fuel tank vent.

Significant Factors:

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

1. The deteriorated condition of the right inner fuel tank bladder resulted in a fuel leak when there was a significant quantity in the tank.

2. An inspection for the issue of a Certificate of Airworthiness, three months prior to the accident, did not detect the deteriorated condition of the right inner fuel tank.

3. The right inner fuel tank compartment in which the tank bladder was located, was not fitted with a discrete drain system.

4. Fuel leaked from the right inner fuel tank compartment into the cabin underfloor area.

5. Pre-flight inspection by the pilot-in-command was inadequate.

6. The engines were inadvertently over primed during the pre-start procedure, resulting in a loss of fuel.

7. The pilot-in-command attempted an engine start in an area where a fuel spill had occurred.

Recommendations:

1. The Civil Aviation Authority review the certification requirements for PA31-P aircraft in respect of the provision of discrete drains in fuel tank compartments.

The instructor stated that after a normal flight and circuit approximately half air brake was set for the approach. Additionally during the approach further air brake was set, for a short period, to steepen the approach. When the instructor then checked the indicated airspeed he observed that it had reduced to less than 45 knots. He stated that he did not close the air brake in time to prevent a heavy landing. This accident was not the subject of an on-site investigation.

Circumstances:

The pilot was making an approach to a cathode protection point on the pipeline to set down the engineer. The selected alighting point was on the slope of a saddle and the aircraft descended until the right skid was on the ground. As he lowered the collective to rest the left skid, he felt that the slope was excessive for a landing. Accordingly, he flew the helicopter up to an in-ground-effect (IGE) hover at about four to five feet and made a left pedal turn through about 90 degrees to move to a more level site further downhill. Seconds later after starting to hover-taxi, the pilot reported a shudder and noticed that the main rotor RPM was decreasing. Despite the introduction of power without collective input, the helicopter continued to descend. The pilot was unable to prevent the helicopter touching down and, after a series of skips and touches, the helicopter crashed in a nose-down attitude and came to rest on its right side. Both occupants exited without assistance through the pilot's side door. The pilot later reported that he felt the throttle travel to its full limit and believed that he was not getting the full power output from the engine. Subsequent engineering investigation of the aircraft did not reveal any anomalies or faults that could have contributed to the accident. Further investigation indicated that the pilot had had a poor night's sleep due to apprehension about the forthcoming tasks for the day. In addition, he had been concerned about family matters due to his unaccompanied move to gain employment. At the time of the accident, he had been flying for about seven hours. The nature of the operation undertaken with frequent landings at difficult sites is conducive to skill fatigue. Skill fatigue is defined as the deterioration in performance caused by work that demands persistent concentration and a high degree of skill. It is an insidious phenomenon associated with failure of memory, judgement, integrating ability and presence of mind. Its effects may occur in conjunction with, and be accentuated by, other factors such as sleep loss. The prevailing conditions at the site chosen for landing were such that the helicopter was facing downwind after the completion of the pedal turn and was in a high power and weight configuration. It is possible that at some stage during the turn the main rotor rpm drooped. The pilot did not become aware that the rotor was in an overpitched condition until the rotor rpm had drooped so low that full throttle would not have been sufficient to prevent ground contact. The nature of the terrain was such that a safe landing was not possible under the prevailing conditions.

Significant Factors:

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

1. The pilot was probably suffering from skill fatigue.

2. The pilot did not realise that he was close to the limits of operation of the helicopter under the prevailing conditions.

3. The pilot probably overpitched the rotors at a height insufficient for recovery in an attempt to regain control of the helicopter.

4. The terrain was such that a safe landing was not possible.

Recommendations:

1. That the Bureau of Air Safety Investigation and the Civil Aviation Authority prominently publish the circumstances and causes of this accident for the education of helicopter pilots.

The pilot had been airborne for about forty minutes when he decided to outland to talk to the ground mustering party. He selected a strip of ground, as an Authorised Landing Area, with sparse low mulga scrub on the sides and a patch at the end of the proposed landing area. Although the pilot overflew the selected area to check for obstructions, he did not carry out his customary low level inspection of the landing surface. The subsequent landing roll was reported to be smooth and uneventful. After talking with the ground party, they departed and the pilot elected to take off in the opposite direction to his landing as there was nil wind. About halfway down the strip on the takeoff roll, the pilot felt the left wheel strike an obstruction and the aircraft slewed to the left. It then ran through some mulga, about 35 metres to the left of the centre of the strip, as it paralleled the takeoff direction. The pilot recalled seeing an airspeed of about 40 knots at this point and as the aircraft was now clear of the scrub, he decided to continue the takeoff. The aircraft was recovered without further incident. The accident was not the subject of an on-scene investigation and the above information was provided by the pilot. Although the pilot's decision to continue with the takeoff did not contribute to the cause of the accident, it is considered that this was an error of judgement on his behalf. Subsequent examination of the damage revealed, amongst other things, that the right elevator balance horn had been torn off. Such damage could easily have led to control surface flutter, component failure and loss of control.

Circumstances:

The pilot was mustering cattle to clear rising flood waters. A second pilot was on the flight to assist and to observe the first pilot's methods of operation. The aircraft was landed near a gate to allow the second pilot to disembark, open the gate and provide further assistance from the ground. The aircraft then took off and the pilot mustered cattle for about the next 15 minutes. The approach prior to the accident was made from the North at about 15 feet with a wind of about 360 degrees at 15 knots. After passing over the cattle, the aircraft pulled up to about 100 feet and levelled for about three seconds. The cattle were now behind and to the right of the aircraft. The left wing and the nose dropped, and the aircraft entered a steep, descending turn to the left until it hit the ground. No pre-accident defects were found with the aircraft. A search of the aircraft logbooks revealed no discrepancies which could have contributed to the accident. Discussions with the observer pilot and pilots who had conducted initial mustering endorsement and subsequent training, indicated a lack of awareness in their own training of airspeed judgement when flying near the ground. Little importance seems to be attached to the different ground speeds when flying into or down wind and the associated perception of airspeed, while the airspeed indicator seems to be largely ignored with wind sound changes used to judge airspeed.

Significant Factors:

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

1. The pilot failed to maintain airspeed.

2. The aircraft entered an inadvertent stall with insufficient height to recover.

3. Pilot training. It is likely that the pilot's training had not placed sufficient stress on the effects of low level manoeuvering in windy conditions whilst relying on airspeed judgement from ground features.

Recommendations:

1. It is recommended that the Civil Aviation Authority surveillance of instructors conducting cattle mustering endorsements, ensure that both ground and air instruction covers the effects of manoeuvering at low level in windy conditions, particularly the awareness of airspeed. Reference CAO Section 29.10 Appendix 1 paragraphs 2(b) (ii) and 2(b) (iii).

Circumstances:

The aircraft was conducting a scenic flight over an area of Lake Eyre North, where the surface of the lake is 30-40 feet below sea level. Weather conditions were fine. High cloud and calm conditions resulted in a glassy lake surface with diminished horizon definition. Passengers on the flight reported that the pilot had mentioned the possibility of flying below sea level, and later when approaching the lake, he remarked that it would be "tricky" without a horizon. He gave no indication that the aircraft was experiencing any difficulties which would affect its ability to maintain flight. The aircraft contacted the lake in a near level attitude, and in cruise configuration. The nearest landfall was twelve kilometres distant, and after several hours the passengers were reached and assisted by a rescue party. Rescue attempts by helicopters were abandoned when unable to safely hover due to the illusory effects created by the glassy surface. The passengers had not been provided with the required flotation safety equipment for this particular flight.

Significant Factors:

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

1. The pilot attempted to cross the lake at an extremely low level.

2. The pilot had insufficient experience to recognise the danger of the prevailing conditions.

3. The pilot was unable to maintain an adequate definition of the lake surface, due to visual illusions created by the glassy water surface conditions.

Recommendations:

1. It is recommended that the Civil Aviation Authority publish an article in the Aviation Safety Digest addressing the dangers inherent in low flight, particularly the visual illusions created by areas of water during calm conditions.

2. It is recommended that the Civil Aviation Authority publish an article in the Aviation Safety Digest to emphasise the requirement for the carriage of flotation equipment in accordance with CAR 258 and CAO 20.11 with respect to areas of water other than ocean. This accident was not the subject of an on-scene investigation.

Shortly after takeoff and while climbing through 2000 feet at approximately 90 kts in light to moderate turbulence, the aircraft encountered unforecast, unavoidable severe turbulence. The aircraft suddenly rolled approximately 75 degrees to the left, and the pilot applied full right control wheel rotation and full right rudder. Control was regained, but during the latter part of the flight the pilot noticed a change in the directional flight characteristics of the aircraft. The turbulence appeared to have been associated with the development of localised "dust devils" or "willy-willies", which had not reached the visible stage. Subsequent examination of the aircraft revealed distortions in the right wing and empennage, consistent with the aircraft having suffered excessive inflight loads. The horn balance of the right elevator was bent, and the internal balance weight was loose. Weather conditions at the time of the occurrence were scattered cumulus, base 5000 feet; visibility 40 kms; surface wind, a gusty south-easterly; and temperature 25 degrees. The Manoeuvering Speed, Va, was estimated to be 100 kts for the weight of the aircraft at the time the turbulence was encountered.

The pilot was making an approach in light wind conditions to a 600 metre long strip. Undulations on the surface were such that the slope in the landing direction varied from about 7 up to 4 down. The pilot was using a short-field landing technique. Touchdown occurred just prior to the threshold, and the aircraft bounced. Full power was applied, but the aircraft then touched down heavily 100 metres in from the threshold. The noseleg broke at the fork, the propeller struck the ground several times and the aircraft came to rest at the edge of the strip. The strip did not meet the published requirements for an ALA suitable for Private category operations. The premature touchdown short of the threshold may have resulted from visual illusions associated with the strip slope. The aircraft had stalled during the attempted recovery from the bounce after initial touchdown.

The pilot attempted to takeoff on an access track to a cattleyard. A southerly wind of about 15 knots necessitated take-off to the south, towards the yard. The aircraft was near gross weight and short-field technique was used. At a position 411 metres from the brakes-release point, the right brake caliper assembly struck a 1.65 metre high section of fence which formed the cattleyard. The right wing sheared off outboard of the fuel tank when it hit an adjacent 3 metre high fence cap. The aircraft then impacted the ground in a steep nose down attitude and slid inverted for a short distance before coming to rest. The aircraft had been airborne for 155 metres prior to the first impact. The pilot did not consult performance charts and underestimated the distance required for the aircraft to safely complete the take-off at this weight. There was sufficient room available for the pilot to taxi the aircraft at least a further 300 metres along the track to the north before attempting the take-off. A properly constructed, serviceable airstrip was located within 500 metres of the cattleyard.