The helicopter pilot was being examined by a Civil Aviation Authority Examiner of Airmen for a rappelling endorsement. The helicopter and crew were also involved in rappelling refresher training for police crewmen. While the helicopter was in a stable hover at 80 feet AGL over an obstacle free area and in ideal weather conditions, two trained crewmen rappelled from the helicopter. Both crewmen departed the helicopter simultaneously but the crewman on the right side misjudged the time for braking before ground contact and struck the ground heavily.

When the aircraft arrived in the destination area, another aircraft was also in the circuit. The pilots were in communication with each other, and arranged that VH-CUO would land after the other aircraft. However, the pilot of VH-CUO apparently misjudged the relative speeds of the two aircraft. He initiated a go-around from a position on final approach to runway 15, when there was evidently insufficient separation with the preceding aircraft to allow a normal landing. The aircraft remained at a low height above the ground, and the pilot broadcast a message that he intended to land in the opposite direction, on runway 33. The wind at the time was from the south-east at about 10 knots. Witnesses observed the aircraft as it tracked along the western side of the runway. The turn onto base leg was made at an angle of bank of about 60 degrees, and about three-quarters of the way around the turn, the nose of the aircraft dropped rapidly. The aircraft then dived steeply to the ground, and was destroyed by the impact and subsequent fire. The subsequent investigation did not reveal any defect or malfunction which might have affected the operation of the aircraft. The pilot was conducting an operation known as a "bank run", and there is pressure on pilots performing such runs to adhere to the prescribed schedules. The pilot's decision to perform a low level circuit and land downwind was considered to be related to his desire to arrive at the terminal as close as possible to the scheduled time. While conducting the circuit, the aircraft stalled during a turn at a height which was too low to allow the pilot to recover control before impact with the ground.

Circumstances:

The aircraft was engaged in the final stages of a pasture spraying operation. The area of operation was a small field surrounded by trees. A powerline was located beyond the trees at the southern end of the field. After committing the aircraft to a low-level pass towards the south, the pilot remembered the partially concealed powerline but was unsure of its exact position. When the powerline became visible against the skyline, the pilot realised that he would be unable to pull up over it and elected to fly through the treetops beneath the powerline. Right wing impact with the trees caused the aircraft to yaw and the rudder to strike the powerline as the aircraft passed beneath it. Despite right wing and rudder damage, the pilot retained control and landed the aircraft in the adjacent paddock where he evacuated the aircraft without assistance or injury. Examination of the aircraft determined that there were no pre-existing mechanical defects, abnormalities or damage which can be considered as factors in, or contributory to, this accident. The pilot acknowledged that he did not conduct a specific check of powerline positions before commencing the clean-up run. The pilot had re-commenced agricultural flying, three weeks prior to the accident, after approximately 9 months of fish spotting operations.

Significant Factors:

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

1. The Pilot-in-command failed to conduct a "Supplementary Wire Hazard Check" prior to commencing the clean-up run.

2. The Pilot-in-command lacked recent calendar experience in agricultural operations and below obstruction height flying. 

Recommendations:

1. That the Civil Aviation Authority give consideration to reducing the calendar period nominated in Civil Aviation Orders section 40.6 para 11, "Recent Experience Requirements", from 12 months to 90 days.

2. That the Civil Aviation Authority specify a syllabus for, and the qualification of the person conducting, agricultural proficiency checks in accordance with Civil Aviation Order 40.6.

During the flight the pilot reported that he would descend to cruise at 500 feet above ground level. Witnesses saw an aircraft at low level on the expected track, and others heard aircraft noise and then the sound of an impact. Weather conditions were overcast with low cloud covering the hills. The wreckage was found at an elevation of about 4300 feet above mean sea level. The aircraft had apparently struck the ground while in a steep nosedown attitude and rotating to the right. A fire had broken out and engulfed the wreckage. Investigation did not reveal any defect or malfunction of the aircraft which might have contributed to the development of the accident. Both engines were operating at high power settings and the gear and flaps were up. The aircraft had been operating under the Instrument Flight Rules when the pilot reported his intention to descend. Conditions at the destination were suitable for visual flight, and the reason the pilot elected to proceed at a low height above the ground was not determined. It was likely that while cruising below the cloud, the pilot was suddenly confronted by localised adverse weather conditions in the vicinity of the accident site. The maintenance of control of the aircraft under these conditions should have presented little problem to the pilot, who was suitably qualified to operate in instrument conditions. In these circumstances, the precise sequence of events leading to the evident loss of control of the aircraft could not be established.

Circumstances:

The helicopter was hovering at a height of 35 ft as part of a training exercise to provide a doctor and a paramedic with experience in winching procedures. The doctor, who was in the sling suspended on the winch cable, was raised to within 5 ft of the helicopter when there was an uncommanded firing of the explosive cable cutter. The doctor fell 30 ft and sustained serious injuries. Investigation revealed the uncommanded firing had resulted from a short circuit in the winch electrical system caused by a blown power resistor in the winch motor circuit. This allowed a substantial current flow in the cable cutter, sufficient to fire the squib. The current flow was not contained within the body of the hoist because of poor bonding between the winch motor and its mounting. The resistor failed due to inadequate heat dissipation at high current flow. The Civil Aviation Authority (CAA) subsequently issued a mandatory requirement to remove pyrotechnic cable cutting devices from helicopter hoists when used to raise or lower personnel. Additionally, both the CAA and the manufacturer have issued mandatory requirements to rectify the bonding problem pending a technical solution to preclude power resistor overheating.

Significant Factors:

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

1. Inadequate heat dissipation of the motor power resistor resulted in the failure of the resistor at high current load.

2. Inadequate bonding (high resistance) between the hoist, mount and airframe caused the current to flow through the squib (low resistance), resulting in uncommanded activation of the squib.

Recommendations:

1. That the CAA evaluate all hoist types for potentially similar problems.

2. That the CAA consider a modification of hoist circuit control to isolate the cable cutter squib by means of a close proximity relay to prevent stray currents from firing the squib.

3. That the CAA amend or re-issue Airworthiness Directive AD/SUPP/12 to activate squibs for all operations other than training exercises when personnel are to be winched.

4. That the CAA amend Civil Aviation Order 29.11 to include in the personnel briefing that a pyrotechnic cutting device is installed and will be used if required during an emergency.

No Summary

Prior to DEPARTURE the pilot ascertained that there was about 23 litres of fuel in the left tank and 91 in the right tank. Take off was with the left tank selected and spray operations commenced. Two paddocks were sprayed and half way along a clean up run to finish off the areas the engine failed due to use of all the fuel from the left tank. The pilot switched to the right tank with the boost on and turned left towards a clear area. The engine did not respond and after about 160 degrees of turn the left wing struck the ground and the aircraft slid to a stop. Had the pilot stopped the turn and levelled the wings earlier the aircraft would have struck trees.

During the downwind leg of the circuit, the pilot heard a sharp cracking noise, which was accompanied by a vibration in the airframe. He also noted that the transmission oil pressure warning light had illuminated. A precautionary landing was carried out, and an initial inspection revealed that a transmission cowling had become detached in flight. The cowling had struck the main rotor disc, and a piece of debris had then hit a tail rotor blade. The design of the latches of the cowling is such that they can appear to be locked when they are actually in an unsecured position. It was possible that the pilot had not fully secured the cowling during his pre-flight inspection. However, the locks were not recovered and the precise reason for the cowling opening in flight could not be established. A detailed examination failed to reveal any reason for the illumination of the oil pressure warning light. It was likely that the warning was spurious, probably being generated by moisture around the pressure sensing switch wiring.

The aircraft had previously had to be flown with the control stick displaced to the right of centre in order to maintain a wings level attitude. The aircraft owner advised a visiting ultralight pilot of the problem, who offered to attempt rectification. After conducting a flight to experience the problem first hand, the pilot adjusted the right wing warping wire and conducted another test flight. The adjustment had improved the trim problem but still not completely provided a fix. The pilot then readjusted the right wing warping wire to its original condition and added a D-shackle to the left wing warping wire to increase its length. Another test flight was carried out and it was found that the aircraft could only be maintained in level flight when full right rudder and full right control stick were applied. The aircraft was struck by a wind gust and the left wing dropped, as no further control was available to correct this situation, the pilot pulled a wing warping wire. Unfortunately he pulled the right wire instead of the left wire and was unable to correct his error before the aircraft struck the ground. A subsequent inspection of the wreckage found that the right wing warping wire was 19 millimetres longer than the left. Also, all the dimensions of the right wing were slightly larger than that of the left wing, resulting in the right wing area being about 80 square centimetres greater.

The pilot was approaching to land in strong crosswind conditions. The area near the threshold of the strip was obstructed by machinery and another glider, and the usable strip width was reduced because of long grass. Although there was adequate strip length, the pilot elected to land close to the other glider. During the landing flare the aircraft drifted towards the obstructions, and the pilot raised one wing in an effort to avoid them. The other wing entered the long grass and the aircraft slewed sharply before falling to the ground.