Wirestrike

The Bell 206 helicopter was engaged in aerial spraying of a property. The pilot had earlier carried out a ground inspection with the landowner to confirm the areas to be sprayed, and to identify obstacles. He then conducted an aerial survey before commencing spraying operations.

Because one of the treatment areas contained powerlines, the pilot decided to spray this area first. He planned to work from east to west, spraying on northerly tracks. This required the helicopter to descend over powerlines crossing the southern end of the treatment area. The height of the powerlines increased towards the western edge of the treatment area. Light coloured shade cloth covered part of the northern section of the area, forming a visual backdrop to the powerlines for much of their length.

The pilot descended to commence the 12th and final spray run along the western boundary, an area which did not have a shade cloth background, making the powerlines less distinct. He failed to notice the increased powerline height, which resulted in the helicopter, travelling at about 20 kts, colliding with a powerline at a height of about 30 ft.

A powerline passed between the landing skids and the fuselage, striking the forward cross tube. The helicopter pitched down, resulting in the main rotor blades slicing off the tail boom as the main rotor assembly separated from the mast, before the fuselage struck the ground. The pilot reported that the engine continued running after ground impact but there was no fire. Protected by a full safety harness and helmet, the pilot was able to escape from the wreckage with the assistance of a bystander. The helicopter's Emergency Locator Transmitter did not activate.

The Piper Pawnee aircraft was conducting spraying operations on a property. The landowner had provided a map of the treatment area, and the pilot had conducted an in-flight inspection. Spray runs were to be conducted at right angles to a powerline running along the boundary of the area to be treated, with the aircraft climbing over the powerline before carrying out a procedure turn and descending to commence another run.

The aircraft was fitted with a Global Positioning System (GPS) to provide track guidance to the pilot during the spray runs. The pilot reported that during the initial spray runs his attention was drawn to the GPS Marking System due to alignment errors. Following the procedure turn after the fifth spray run, the pilot reported he momentarily forgot about the presence of the powerline and descended into it. The landing gear snagged the wire, causing the aircraft to lose airspeed and strike the ground in an almost level attitude. The left wing and fuselage were damaged during the ensuing ground run. The pilot, who was wearing a full harness, was unhurt.  An Emergency Locator Transmitter (ELT) was not fitted to the aircraft.

The pilot reported that he commenced take-off into the east with a three knot tailwind. The strip was approximately one mile long with a powerline at the eastern end which could be flown under if necessary. The aircraft was loaded with 600 lts of water and 80 lts of fuel. Halfway through the take-off the pilot decided to go under the powerline.

After lift off the pilot allowed the aircraft to climb slightly instead of keeping it low enough to pass under the powerline. He said that despite lowering the nose, the aircraft got too high to safely pass under the wire. The top wing of the aircraft hit the powerline resulting in the aircraft becoming uncontrollable. It stalled and hit the ground in a steep nose down attitude, banked to the left.

Factual Information

The flight was conducted from a grass strip about 1,000 m long oriented 060/240 degrees M and operated by a parachuting club. The wind was from the south-west at 10-20 kts.

Witnesses reported that, as the pilot commenced to taxi the aircraft from its hangar to the loading position, the propeller struck the ground. It was not clear whether the impact was sufficient to stop the rotation of the propeller. The aircraft was pulled clear of the area and the propeller examined by the pilot and the jumpmaster. The jumpmaster indicated that the blades appeared to have retained their shape and were intact. However, at his suggestion, the pilot flew a circuit to check the aircraft's performance. The pilot indicated that the aircraft performed normally. Neither the pilot in command nor the jumpmaster were qualified to inspect the propeller in accordance with Civil Aviation Order Part 106 which details the inspections to be conducted following a propeller strike.

Four parachutists then boarded the aircraft. They reported that the ground roll required for the aircraft to take off seemed to be longer, and the aircraft climbed at a shallower angle, than they had previously experienced, however, the engine sounded normal. At what they thought was about 200 ft above ground level, they heard the pilot say that the engine had lost power. He then commenced to turn the aircraft to the left. When the aircraft was aligned with the strip, one of the parachutists called for the pilot to lower the flaps.

Ground witnesses saw the aircraft turn left and approach the strip downwind. The aircraft touched down about halfway along the strip but immediately became airborne again and commenced a shallow climb with a nose-high attitude. The flaps were observed to be in the fully extended position and the aircraft was rolling left and then right. About 300 m beyond the end of the strip, the aircraft struck powerlines 8 m above ground level, then collided with the ground at a steep nose-down angle and was destroyed by impact forces.

The aircraft was fuelled to capacity a few weeks before the accident. There was no evidence to suggest that it had been flown or defueled in the intervening period. The weight of the aircraft at take-off was calculated to be approximately 1,198 kg. This compares with its maximum take-off weight of 1,043 kg.

Examination of the propeller revealed damage to both blades. While some damage appeared to be consistent with the propeller strike during taxi, other damage may have been caused by impact with the ground following the wire strike. Examination of the flaps confirmed that they were fully extended at impact. There was no evidence of any other condition which might have affected the operation of the aircraft.

The aircraft was fitted with only the pilot's seat as it is common practice in parachute operations to remove all other seating. While the pilot's seat was fitted with a lap-sash safety harness, there was no evidence of the presence of safety harnesses or restraints available to the parachutists for the accident flight. Some of the parachutists on board the aircraft advised that it is common practice for parachutists not to wear safety harnesses because of their potential to hinder egress from the aircraft.

The pilot was unable to be interviewed during the course of the investigation. As far as could be determined, his flying experience in the few months before the accident was limited to the conduct of parachute dropping flights from the airstrip on some weekends. His experience on the aircraft type could not be established.

Analysis

There was insufficient evidence to draw any conclusion concerning what affect, if any, the propeller ground strike had on the performance of the aircraft. However, the take-off and climb performance of the aircraft with the parachutists on board would have been significantly less than that which the pilot had experienced during the check flight which had been conducted a short time earlier. The difference in performance may have been sufficient to lead him to believe that the engine had lost power.

The attempt to land downwind in the prevailing conditions contributed to a higher-than-normal approach profile and approach speed.  Similarly, the subsequent attempt to go around with the flaps fully extended resulted in a shallow climb gradient. The observed rolling motions of the aircraft were consistent with it operating close to the stalling speed. The nose-high attitude of the aircraft may have prevented the pilot in command from seeing the power lines.

The purpose of the flight was to aero tow a glider from a paddock where it had made an out landing. Prior to take-off the pilot measured the paddock twice by pacing. The paddock was wedge shaped with powerlines running along the two longer boundaries. There was also a powerline spanning the paddock towards the narrow end of the wedge. Despite walking under this powerline while pacing the paddock, the pilot did not see it.

Take-off was into the northwest which provided the longest take-off run and was also into a 5-7 kt wind. After take-off the pilot held the tug down to gain speed. He then saw the powerline but too late to avoid it. After impact with the powerline the tug hit the ground and was substantially damaged.

The pilot said that in the take-off direction, the powerline was below the horizon against a background of hills which made it almost impossible to see.

Due to poor lift conditions the pilot was forced to make an outlanding. He selected what appeared to be a suitable paddock and noted there was a powerline running parallel to the selected landing direction. Late on final approach, the glider hit another powerline that the pilot had not seen. This line was a three-wire spur line crossing the landing path at 90 degrees and originating from an area of trees.

Significant Factors

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

1 The pilot had to make an outlanding due to poor lift conditions.

2 The pilot did not see the powerline before his aircraft collided with it.

The helicopter had been engaged in a low-level survey for approximately four hours. As the pilot commenced to climb at 60 kts to return to the helipad for refuelling, he saw a single-strand powerline, at an oblique angle, about 30 ft in front of the aircraft. In an attempt to avoid the wire, the pilot rolled the helicopter to the right and pushed the nose down. However, a loud bang was heard, and the aircraft yawed to the left. The pilot centralised the controls, transmitted a MAYDAY call on the company frequency, and informed the passengers to prepare for a forced landing. He successfully carried out a flat approach and "run-on" landing in a nearby clearing. At the time of the accident the weather was fine. The pilot described the visibility as good, with the position of the sun approximately overhead.

A damage inspection of the aircraft revealed slash marks on the main rotors consistent with those of a wire strike. The powerline had sliced through the upper left cabin area, and the arm of a winch located above the left passenger door had been pulled and twisted. The wire appeared to have temporarily wrapped around the exhaust before unravelling and falling clear.

The pilot reported he had been notified of the task the day before, and as part of his flight planning routine, had consulted local employees from his company. Although he had flown in the same area some months before, he had not seen the powerline, and nobody he spoke to appeared to have any knowledge of its presence. Whilst a general survey of the area was carried out in preparation for the flight, the pilot advised he was not able to complete a high-level reconnaissance due to the nature of the operation.

The pilot had accumulated considerable experience in low level flight operations. Although he carried aeronautical charts for the area in the aircraft, they did not indicate the position of the powerline.

The powerline was a single wire earth return line type, the property of an electricity authority, and had been erected some 30 years ago. In the area in which the helicopter was operating the supporting poles were approximately 1.4 km apart, where the powerline spanned a gully. The aircraft struck the powerline some 700 m from the nearest pole, whilst climbing out of the gully, some 300 ft above ground level. The powerline was not fitted with any warning markers.

The pilot carried out an inspection of a paddock and its surrounds prior to commencing the aerial application of insecticide. Three powerlines were identified, two within the paddock and another just outside a nearby fence line. The pilot reported that all three powerlines were checked for spur lines and T-junctions, as well as for aircraft clearance during the spray runs. The area in which the spray runs were being carried out was described as undulating, with a line of trees to the east, parallel to the flight path of the aircraft.

Five spray runs were subsequently carried out in a north-south direction at a height of about six feet. This required the aircraft to be flown beneath the powerlines, the first of which lay in an east-west direction. On the sixth run, as the aircraft approached the first powerline, the pilot reported that he encountered some turbulence. The aircraft struck the powerline, but the pilot was able to maintain control and land on the property.

A damage inspection by the pilot revealed that the right-wing tip leading edge had been slightly bent, the windscreen was broken, and the propeller had sustained minor damage. He assessed that the aircraft was able to be flown to another location, where repairs were carried out. The weather was described by the pilot as fine, with a light south-easterly wind at approximately 8 kts, and scattered cloud.

The pilot was conducting a noxious plant inspection and contour flying about 50 ft above hilly terrain at an indicated airspeed of 20kts to 25 kts.

The helicopter struck a single powerline which slide up the bubble and contacted the flying controls before breaking. Although cyclic control was partially lost, the pilot was able to land the helicopter without further incident.

The powerline had a span of approximately 200 metres between supporting poles and was difficult to detect from the air.