Wirestrike

The aircraft departed private property located at Tates Straight on Lake Burrinjuck NSW for Cootamundra NSW at about 1730 ESuT. On board were the pilot and two passengers. After take-off the helicopter was seen to transit at a low altitude in a northerly direction. Three to four minutes after the helicopter departed, witnesses heard a sound like a muffled gunshot and shortly after, smoke was seen to rise from the direction in which the helicopter was headed.

The accident site was located in a valley about 3.5 km from the point of departure. The ground level at the south end, the direction from which the helicopter approached, was the highest ground elevation along the flight path. From this point the valley floor descended relatively steeply, and the upper ridges of the valley sloped more gently with the distance between the ridges widening along the direction of flight. Trees about 15 m in height covered the valley and ridges

Weather conditions observed at the lake were fine with little or no wind.

The main aircraft wreckage was located in the centre of the valley. Wreckage was distributed for a distance of about 180 m in the direction of flight, from an area adjacent to the estimated position of a power line which was suspended across the valley. The majority of the wreckage was located under the flight path. However, the main rotor head with three blades attached, two separated main blades, and the tail rotor gearbox with damaged blades were distributed adjacent to the flight path. The fuselage and the main transmission were located about 180 m from the power line and were consumed by fire. The aircraft had descended at an angle of about 15 degrees through the tree canopy. After striking the ground, it slid about 10 m before coming to rest. The engine was located about 13 m beyond the fuselage. The three persons on board received fatal injuries.

About 1 km from the south end of the valley, a power line extended across the valley at right angles to the direction of flight. The power poles were located on the tops of each ridge which resulted in a wire suspension distance of about 832 m. The east ridge is about 510 m AMSL, and the west ridge is about 480 m AMSL. The wreckage was located at about 380 m AMSL or between 100 and 120 m below the ridge heights. The power poles were located in clear spaces among the trees at the top of each ridge and could only be observed from a position in line with the suspended wire. The conductor was 4.2 mm in diameter and constructed of three strands of steel wire. The wire sag was reported by the electricity company to be about 41 m. The conductor was broken.

Examination of the recovered fuselage and tail boom showed evidence of a wire strike to the area of the helicopter just above the cockpit and repeated main rotor blade strikes to the fuselage and tail boom. The wreckage scatter both in the trees and on the ground was indicative of an in-flight breakup. There was no evidence of in-flight fire.

The engine exhibited signs of high-speed rotation at impact and the damage was consistent with ground impact damage. Failues to the main rotor head, tail rotor and gearbox, and rotor blades were analysed as overload failures.

It could not be determined why the pilot departed to the north rather than to the north west direct to Cootamundra, nor why he was conducting the flight at an altitude which placed the aircraft below the valley ridge lines.

The sun was positioned left of and at near right angles to the direction of flight and would not have interfered with the pilot's vision. The wire conductor was dull and would not have reflected sunlight. Consequently, the wire would blend in with the background features of trees, grass, water and sky making it difficult for the pilot to see and avoid.

Evidence gathered at the accident site indicated that the helicopter struck the suspended wire conductor while in normal cruise flight at a height of about 60 to 80 m above the ground. Wire contact occurred first on the upper fuselage and then on the main rotor head. The contact would have applied abnormal gyroscopic loads to the main rotor disc. These loads would result in the blades travelling outside their normal paths and striking the helicopter fuselage and tail boom. Metal components recovered from the fuselage and tail boom, and main rotor blade damage, indicates that there were multiple main rotor blades strikes on the aircraft structure. The main and tail rotors separated from the helicopter before it descended into the trees.

Significant Factors

1. The aircraft was being flown at low altitude and struck a power line.

2. An in flight breakup of the helicopter occurred.

Aircraft hit power lines during go around from one way strip into rising terrain.

At 1703 hours CST on 13 March, 1975 a Cessna 31QN aircraft, registered VH-SDE, struck a 60 feet high radio mast and dived to the ground at Fltzroy Station, Northern Territory. The aircraft was destroyed by Impact forces and subsequent fire and the five occupants were killed.

The aircraft turned slightly to the right and crashed to the ground in a starboard wing down attitude. The main wreckage came to rest in an upright position 130 metres beyond the point of power line contact and a fierce fire broke out immediately.

Student pilot outside training area made low pass over property. Aircraft struck power lines-pitched to ground.

After take-off, the aircraft circled Moorook and then Kingston -on -Murray after which it headed In a northerly direction until it was again over the Murray River. It then followed the river on a generally westerly heading to Wigley Flat, a small settlement some 22 kilometres east of Waikerie, and, after circling at a low height, continued along the river. As the aircraft followed a bend in the river and was turning to the right, the pilot suddenly saw a power cable immediately ahead but there was insufficient time to take avoiding action before the cable was struck. The aircraft crashed into the river below but the three occupants were able to open the doors and leave the cabin before it sank in deep water.

Aircraft struck newly installed power line. Wing detached and aircraft struck ground and burst into flames.

Early in the day the pilot flew the aircraft from Mudgee to the airstrip situated about 4 mile south of the property on which superphosphate was to be spread. The weather was fine, the wind was calm and visibility was unrestricted. Although the pilot did not carry out a ground or aerial inspection of the property prior to commencing operations, nor did he obtain a specific briefing regarding the location of power lines on the property, he had carried out similar operations on this property periodically during the previous five years. As the aircraft approached the power line it banked to the right, apparently to follow the change in boundary direction and the raised left wing tip struck the cables resulting in a portion of the wing leading edge and upper surface fabric being detached. The aircraft slewed and rolled to the left and struck the ground In an inverted attitude 460 feet beyond the power line where it came to rest against a post and wire fence. A fierce fire occurred immediately.

The operation was to spray a sorghum crop in an approximately rectangular field aligned north-east/south-west. There were four isolated trees in the field and a single wire power line was located 80 feet outside and parallel to the north-east boundary. The wire was supported between two poles 890 feet apart and the height of the wire varied between 34 feet above the ground at the pole adjacent to the northern corner of the field and about 24 feet at the centre of the span. The field contained two crops of different ages on alternating contour strips and, as only the younger crop was to be sprayed, it was necessary for the pilot to turn the spray on and off four times on each run along the field which was approximately 3000 feet in length. Because of the curved contours the positions along each run at which the spray control was operated would vary. During the day there were four telephone contacts concerning the proposed operation between representatives of the operator and the farmer or his representative but the farmer did not have the opportunity to speak directly to the pilot and thus brief him regarding the power line. The pilot had not previously treated this particular field but he had operated over adjacent fields and properties. The farmer and a neighbour acted as markers and when the aircraft arrived overhead they moved into positions at either end of the field. The pilot made a brief aerial inspection and commenced operations running north-east and south-west alternately. On each of the first three runs in each direction the aircraft passed under the power line and the circumstances suggest that the pilot was aware of its presence. The seventh run was made towards the north-east and, at its completion, the aircraft commenced to pull in the vicinity of the boundary fence which was earlier than on previous runs. The aircraft then struck the power wire in a nose up, port wing down attitude. The wire became caught on a flood light which was mounted on the underside of the port wing. The aircraft veered sharply to the left before the wire wrenched out the light and the internal wing drag strut assembly on which the light was mounted. The aircraft continued rolling to the left as it climbed to a height of about 50 feet and it then dived into the ground in an inverted steep nose down attitude and burst into flames.

During the afternoon the aircraft had been flown to the property of a friend of the pilot, 36 miles to the north east of Kellerberrin and whilst there, had been flown by the property owner. A few minutes after departing on the return flight the aircraft was seen circling at a height of about 500 feet over the property of another friend of the pilot some 15 miles north of the direct track to Kellerberrin and it then departed in the general direction of its destination. The aircraft was next sighted by the owner of this property who had not been at home when the aircraft first circled his house, but was returning there by car from Doodlakine. He saw the aircraft for a short period, flying at 600 to 800 feet above ground level, about one third of a mile to the right of the road on which he was travelling and on a parallel northerly course. He then lost sight of the aircraft because of trees lining the road. After travelling for a further two miles to the north, the property owner made a 90 degree turn to the right and from this road he had a clear view across the paddocks to the south. He sighted the overturned wreckage of the aircraft approximately one mile to the south of his position and some 150 feet east of the alignment of the road which he had just left. The aircraft undercarriage had caught the top wire of a power transmission line which crossed the paddock from east to west at a height of about 30 feet. The aircraft had then pitched sharply nose down and had struck the ground in an almost vertical attitude 145 feet north of the point of contact with the wire. The nose dug in to the surface of the paddock which was soft from recent rains. The engine was torn from the airframe and the main wreckage came to rest inverted some 36 feet beyond the area of initial impact with the ground. Examination of the wreckage showed that the flaps were up. There was no defect discovered in the aircraft which could have contributed to the accident and there is evidence that the engine was operating normally up to the time of impact.