Wirestrike

The aircraft was engaged in an agricultural operation. The pilot having surveyed the property from the air and received on-site information from an agent on the ground by UHF radio, was aware of the many wires and other obstacles in the area.

On the initial swarth run the pilot failed to notice a single wire earth return line suspended between 15 and 18 metres above the ground, with a span of about 1000 metres. The aircraft struck the wire with the landing gear, decelerated rapidly and impacted the ground in a steep nose-down attitude.

Before spraying a field cultivated with tomatoes, the pilot made a ground inspection to note the position of powerlines and other obstacles. Not long before departing on the spraying job, he was asked to spray an additional block in the same vicinity.

He completed spraying the first paddock without incident and moved onto the next block where he conducted an aerial inspection for obstacles. He noted that the same powerline crossed this block as well as the previous cultivation. He did not notice that one of the three wires was hanging lower than the other two. During his last spray run, which co-incided with the centre of a span, the helicopter collided with the lower wire and plunged into the ground.

Initial advice of this occurrence indicated that the accident had involved the aircraft striking a powerline during a practice forced landing. The pilot received a serious injury and spent some time in hospital recovering.

Subsequently, the Civil Aviation Authority advised that they had received information that the accident had resulted from a breach of the Civil Aviation Regulations, and they were pursuing the matter along those lines. Consequently, the Bureau did not continue its investigation of the occurrence.

The pilot had been briefed on a number of treatment areas some days earlier. When he approached this area, he did not see the powerline. At the end of the first spray run he flew into the wire. The helicopter developed a vibration, and the pilot landed as soon as possible.

Inspection found that one main rotor and one tail rotor blade was damaged and required replacement.

He had been advised of the presence of the wire during the earlier briefing.

During a cattle muster along a laneway, the pilot positioned the helicopter to head off a beast which broke away from the mob. As he descended in front of and to one side of the beast, he felt a sudden vibration through the helicopter and at the same time noticed an overhead powerline.

He lowered the collective for an immediate landing. The landing which followed was heavy, spreading and breaking the skid gear. The helicopter then rolled onto its side. Post flight inspection by the pilot revealed that the tail rotor had struck the wire.

The powerline was a single wire earth return line strung about 35 ft above ground. The span was reported to be 800 m long. The wire was struck some 100 m from the nearest pole which was partially hidden among foliage.

The helicopter was engaged in a search for a missing aircraft. The search area was in a valley bounded by sheer cliffs reaching to heights of 2,000 ft above the valley floor. Whilst the helicopter was flying at a height of 1,000 ft about 150 metres out from a cliff face, the main rotor struck and severed a power transmission spur line. The helicopter remained controllable, and the pilot was able to land in a clearing about two kilometres away for damage assessment.

The pilot reported that he had not seen the cable, which stretched in a single span from the cliff top to the valley floor, nor had he experienced any handling difficulties with the helicopter after the collision.

The pilot was flying the helicopter in a spraying operation over a paddock adjacent to a farmhouse. A study of his map and an aerial inspection had led him to believe that a major spur powerline terminated at a transformer near the farmhouse. However, this was not the case as the three-phase powerline continued on in long spans.

He had almost finished the task and required one final spray run at 90 degrees to his previous swaths and the unseen powerline bordering the paddock. As he pulled up after the run, the spray boom collected the wires. The helicopter gyrated, losing the tail boom to a main rotor strike, and crashed some 15 metres beyond the powerline.

The pilot had not seen the powerline at any stage.

During a clean-up spray run flown parallel to powerlines, the pilot inadvertently allowed the helicopter to drift to the left into the lines. The main rotor struck the wires and during an attempt by the pilot to turn away, the tail rotor also struck the wires. The tail rotor/gearbox was severed, causing the helicopter to enter an uncontrolled spin to ground impact.

The clean-up run was from west to east, at an airspeed of about 40 kts. The wind was from the north-east at about 2 kts.

The pilot was spraying a cotton crop in light wind conditions. On the second clean-up run, although aware of the location of a powerline, the pilot could not see the wires due to spray drift contamination of the windscreen. He misjudged the pull up point, and the aircraft struck the wires with the right main landing gear.

The aircraft was retarded by the wires and crashed inverted. The pilot was able to extricate himself before the aircraft was destroyed by fire.

On 20 September 2014, the pilot of a Piper PA-25 aircraft, registered VH-CPU, conducted a ferry flight from Camden to Bunyan aeroplane landing area, via Goulburn, New South Wales.

After refuelling at Goulburn aerodrome, the pilot tracked to overhead Michelago and continued south towards Bunyan. About 10 km south of Michelago, the pilot intended to overfly a private airstrip to assess its condition and suitability as a potential out-landing site for gliders operating from Bunyan.

The aircraft was heading south and as the airstrip was oriented approximately north-south, the pilot elected to overfly the runway. When about 300 m beyond the runway threshold, the aircraft struck powerlines that crossed the runway about 15 m above ground level, dislodging the windscreen and canopy. The top of the fin was severed by the powerlines. Immediately after the strike, the aircraft banked to the left before returning to level flight. The pilot assessed that the aircraft was too high to land ahead on the remaining runway and made a right turn, initially planning to land towards the north on the adjacent paddock. However, due to the rough surface of the paddock and tailwind, he conducted a short downwind leg before turning to the right, and the aircraft landed into wind on the runway.

The ability of pilots to detect powerlines depends on the physical characteristics of the powerline and the effect of weather conditions. Powerlines may not be contrasted against the surrounding environment and the wire itself can be beyond the resolving power of the eye. Pilots are advised to use additional cues to identify powerlines, such as the power poles and buildings to which the powerlines may connect.

Aviation Short Investigations Bulletin - Issue 38