Wirestrike

Circumstances

The pilot had arranged to visit the property of a friend in the Kingaroy area. He planned to arrive at the property at about 0900. At 0930, the pilot rang his friend and advised that he would not arrive until 1200-1230. The delay was the result of maintenance needed on the aircraft which required the pilot to fly the aircraft to Caloundra and return to Redcliffe before departing for Kingaroy.

The pilot and his passenger arrived at the property at about 1230 where they lunched and spent the afternoon. When it came time to leave, the property owner decided to accompany his friend in his own Lightwing aircraft for part of the return journey. They boarded their respective aircraft and the Lightwing became airborne and waited in the area for about 10 minutes for the Skyfox to become airborne. The pilots eventually gained radio contact with each other but the pilot of the Skyfox gave no reason for his delayed departure.

Both aircraft set course for Nanango and the Skyfox, which had been above and behind the Lightwing, overtook the other aircraft and they continued at about 2,000 ft above ground level (AGL). The pilot of the Skyfox then

descended his aircraft, followed by the Lightwing, to overfly an old airstrip at an altitude of between 10 ft and 20 ft AGL, before climbing to a reported 2,000 ft AGL. The Skyfox pilot then advised his friend that he was going to overfly another airstrip and descended. The Lightwing remained at altitude. During the descent the pilot of the Lightwing reported seeing a short then continuous stream of whitish smoke from the rear of the aircraft. He attempted to contact the Skyfox pilot by radio but received no response.

The aircraft was observed by a ground witness to complete two to three orbits of a property homestead before commencing a flypast over the homestead in a southerly direction. The witness stated that he did not observe any smoke from the aircraft. He then reported hearing the sound of the two powerline wires coming together and then observing the aircraft with the wings level but in a shallow descent continue in a southerly direction and impact a tree.  The aircraft immediately caught fire and fell to the ground.  The wreckage was completely burnt out.

Site details

The powerline struck by the aircraft was strung between two poles on the top of ridgelines either side of the homestead. The span between the two poles was 560 m and the wires were estimated to have been in excess of 32 m above the ground at the point of impact. The poles were located in trees of a similar height and would have been difficult to see from the aircraft. The distance from the powerline to the tree struck by the aircraft was approximately 160 m.

Aircraft examination

The aircraft was extensively damaged by the post-impact fire. At the point of contact with the wires, the tip of one propeller blade and a piece of window Perspex had been torn from the aircraft. However, the aircraft appeared to have arrived at the impact point substantially intact. No defects were observed with the airframe that could have contributed to the occurrence.

The engine was removed from the aircraft for specialist examination. The examination did not reveal any defects that could have contributed to the accident. The examination of engine accessories was hampered by the intensity of the fire.

Smoke

The opinion of those experienced in the operation and maintenance of similar aircraft indicates that the most likely source of whitish smoke was a leak of engine coolant. The coolant is used to cool the heads of the four cylinders of the engine and a loss of coolant would result in an increase in cylinder head temperature but would not necessitate an immediate landing. The inspection of the engine did not indicate any signs of a loss of coolant, but the fire damage precluded any determination of the serviceability of the coolant system.

Pilot aspects

The pilot had visited the adjoining property, which is located to the east of the accident site, on the day prior to the accident. Both properties were owned by relatives of the passenger in the aircraft. While visiting the property he had discussed with the owner the upgrading of an airstrip, which was currently used in the operation of model aircraft, to a standard suitable for the operation of the Skyfox. Included in the discussion was a briefing by the property owner to the pilot of the wires surrounding the model airstrip. The briefing did not include the existence of the wires struck by the aircraft on the following day. The property owner was expecting the pilot to overfly his property on the morning of the accident. However, the owner of the property on which the accident occurred was unaware who the occupants of the aircraft were until some hours after the accident.

There was no airstrip in the area in which the aircraft was operating prior to its impact with the wires. The wires crossed a ploughed paddock which was unsuitable for the operation of an aircraft.

Analysis

It could not be positively determined if there was any fault with the aircraft prior to it striking the wires.  Likewise, the purpose of the orbits of the homestead near the accident site is unknown.  It is also unknown if the pilot had been previously aware of the existence of the wires struck by the aircraft but forgot about them on this occasion. Regardless, it appears that the pilot did not see the wires in time to avoid the collision.

Significant factors

1. It could not be determined if the pilot was previously aware of the   existence of the powerline struck by the aircraft.
2. The pilot did not see the powerline in sufficient time to avoid the collision.
3. The serviceability state of the aircraft prior to the accident could not be positively determined.

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.