The pilot intended to transport two passengers and their equipment along the Katherine Gorge. The helipad used for take-off was on the side of the gorge, some 40 feet above the river level. The pilot initiated a running take-off on the skids, but the helicopter began to sink as it left the river bank. Full throttle was applied, but without effect. As the helicopter approached the opposite bank at tree-top level, the pilot raised the collective lever in an attempt to clear the trees. The aircraft did not respond and as it continued to sink, the pilot recalled seeing the engine and rotor rpm decay towards the lower limit of the operating range. The helicopter descended into the trees and came to rest on its left side about 400 metres from the take-off point. The pilot subsequently advised that the helicopter had not been performing as well as he had expected during previous flights. Investigation revealed that the engine had been unable to develop rated power output and that the helicopter was some 114 kilograms over the maximum permissible all-up weight. Detailed examination of the turbocharger revealed that various components had suffered severe deterioration. The unit had exceeded its authorised life by nearly 400 hours. It was also likely that pilot operating techniques had contributed to the faults in the turbocharger, in that insufficient engine idling time prior to shutdown had been allowed.

The aircraft was in normal cruise at 1500 feet above sea level when the pilot noted a mild shuddering, and almost immediately the oil pressure reading dropped to zero. Shortly afterwards, the engine began vibrating severely, and the pilot was committed to a forced landing. In the latter stages of the approach the pilot was forced to pull-up to clear powerlines, following which the aircraft descended and struck a tree and a steel mesh fence at the edge of an industrial area. Investigation revealed that the flexible oil line between the engine and oil cooler had failed due to deterioration, resulting in oil starvation and seizure of the engine. Examination of Bureau records revealed three other recent occurrences in New South Wales where the subject hoses have failed in flight. The hoses are currently required to be inspected and tested every six years. However, the manufacturer recommends that the hoses should be replaced every five years or at engine overhaul, whichever comes first. The particular hose which failed had been in service for more than six years.

Circumstances:

The aircraft had been flown twice that day prior to the accident flight. No problems or unserviceabilities had been reported. The purpose of this flight was to take a youth for a joy flight and the passenger emplaned while the engine was still running after the previous flight. After take-off, the aircraft was seen by several witnesses to fly low over the strip and adjoining areas before starting a manoeuvre at low level which resulted in the aircraft apparently stalling. The aircraft was then seen to rotate several times before crashing in a near vertical attitude through several branches of a large tree. Witnesses ran to the aircraft and found the pilot dead, but they were able to free the surviving passenger from the rear seat. It would appear that at the time of the accident, the pilot was carrying out some form of impromptu display at low level or "showing off". The investigation established that the pilot was want, at times, to show off or enjoy "pushing it" or taking an aircraft to its limits. Although it was not possible to determine the exact manoeuvre performed by the pilot which lead to his loss of control, there is no doubt that he carried out a manoeuvre at low level that resulted in the aircraft stalling at a height insufficient for recovery. Such a manoeuvre was apparently induced by the pilot rather than as a result of his experiencing a problem with the aircraft. No faults or anomalies were detected in the aircraft that could have contributed to the accident. All witness evidence is consistent in that the "spin" or spiral occurred after the aircraft entered the turn at low level. During his earlier flight in the aircraft that day, the pilot was reported to have performed aerobatic manoeuvres. The aircraft was not certified for aerobatic flight, and no record was found of the pilot holding an endorsement to perform aerobatic manoeuvres.

Significant Factors:

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

1. The pilot was engaged in an unauthorised impromptu display at low level.

2. The pilot stalled the aircraft at a height insufficient for recovery.

3. The pilot attempted manoeuvres beyond his level of experience.

Recommendations:

It is recommended that the Civil Aviation Authority

1. Require evidence of logbook endorsements for aerobatic manoeuvres, Biennial Flight Reviews, and other logbook only entry qualifications to be recorded on the departmental pilot history file.

The rudder failed when the pilot initiated a climb at the end of a spray run. The rudder was bent over at the top by about 45 degrees, but the pilot was able to maintain control of the aircraft and carry out a safe landing at Dalby. The rudder spar had failed above the top hinge point near a weld which was associated with a modification to replace the single point hinge with a three point hinge. The failure of the spar was caused by the pressure of a crack which had not been detected prior to the welding of the upper hinge modification. This accident was not the subject of an on-site investigation.

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).