On 26 August 2011, at about 1545 Western Standard Time, an Air Tractor Inc. AT-802, registered VH-NIW (NIW), struck power lines during agricultural spraying operations. Earlier that day, at about 0700, the pilot had commenced the first of six scheduled agricultural spraying flights from a private airstrip near Mogumber, Western Australia. At mid-morning, he was approached by a farmer to carry out a seventh (unscheduled) spraying operation of wheat paddocks next to the Bindoon-Moora road. The farmer supplied the pilot with a map of the fields to spray, which included the location of two powerlines. He then loaded the aircraft hopper with the required chemical spray mix and flew to the property.
On reaching the property, the pilot commenced his field inspection. He flew north at 200 ft above ground level (AGL), following the main power line running through the property, then turned south to fly along the edge of the main road. During the inspection, the pilot identified the two powerlines and paddocks marked on the farmer’s map and a third unmarked powerline. At the same time, his attention was diverted to vehicle traffic on the main road located next to the spraying area. The pilot reported that he was concerned that issues might arise from conducting spraying operations close to the traffic.
Taking advantage of a break in the traffic, the pilot manoeuvred NIW in a northerly direction, then flew below the level of the powerlines and commenced spraying operations adjacent to the main road. When about 300 m into the paddock, the aircraft struck an unseen fourth set of powerlines.
After striking the powerlines, the pilot looked to the right and saw electrical arcing from the top of the power pole. He climbed the aircraft up to treetop level, believing it had sustained only minor damage and looked for a suitable area to ‘dump’ the chemical spray. However, the engine lost power, forcing the pilot to immediately jettison the spray load. The aircraft then entered into an uncommanded gradual left turn, which the pilot could not correct. The aircraft, flying left wing low, continued over the main road and struck terrain in a neighbouring paddock. The aircraft sustained serious damage; the pilot was not injured.
The pilot held a Commercial Pilot (Aeroplane) Licence and a valid Class 1 medical certificate. He had a total of 12,757 hours, of which about 5,500 hours were on the AT-802.
The pilot stated that he may have become distracted by the vehicle traffic on the main road, which subsequently diverted his attention away from maintaining a lookout for powerlines.
The pilot also reported that he did not see the power pole hardware associated with the struck line or the house the line was connected to, as they were obscured by trees.
Whether or not the ATSB identifies safety issues in the course of an investigation, relevant organisations may proactively initiate safety action in order to reduce their safety risk. The ATSB has been advised of the following proactive safety action in response to this occurrence.
The operator has advised that the following amendments will be made to the operations manual.
Before entering the field to be treated, the pilot is required to fly around the entire perimeter at least twice to firmly establish the location of wires, stand pipes, or other obstacles.
(a) At least one high recce is to be flown at approximately 500 ft AGL.
(b) At least one low level recce is to be flown at approximately 250 ft AGL.
These amendments will take precedence over the aircraft flight manual
The aircraft operator has advised that they will reinforce with pilots that the operator policy is: ‘do not fly below power line height in the Air Tractor 802 aircraft’.
Wirestrikes pose an ongoing problem to aerial agricultural operations. The joint ATSB and the Aerial Agricultural Association of Australia report, Avoidable accidents No. 2 – Wirestrikes involving known wires: a manageable aerial agriculture hazard, identified 180 wire strike accidents between 2001 and 2010. Of these, 100 involved aerial agricultural operations. Some of the hazards identified in the report that are associated with identification of wires and distractions are set out below.
Identification of Wires
Whether operating into a known or unknown area, it is important that pilots have an up-to-date and detailed map of the area, which clearly identifies powerlines and other hazards. Some pilots of wire strike accidents reported to the ATSB that the maps provided by clients did not have the powerlines clearly marked. Conducting a thorough briefing with the property owner, local residents or other operators with experience in the area will further assist with hazard identification. However, it is important to recognise that a map or briefing alone does not tell the entire story. It is crucial that an aerial inspection of the area is conducted to confirm the locations of wires and hazards. The report further stated:
“Be aware that during the reconnaissance, you may miss spotting some wires as the visual cues are not always reliable or available. For example, power poles often blend into background vegetation, making them difficult to see. Also, don’t rely entirely on the presence of poles or other cues as indicators of wires. If you can see the wire, follow the wire itself to confirm its placement.”
Multi-tasking in aerial agricultural operations is part of the job; however, focusing attention on non-operational tasks or focusing on operational tasks at the wrong time can affect hazard avoidance, detection and reaction times. Research published by the ATSB in 2006 identified 325 occurrences between January 1997 and September 2004 associated with pilot distractions, of which six per cent involved aerial agricultural operations. The Flight Safety Foundation recommends that after a distraction sources has been identified, pilots should re-establish situation awareness by applying the following:
• Identify: What was I doing?
• Ask: Where was I distracted?
• Decide/act: What decision or action shall I take to get ‘back on track’?
This accident highlights the vital role hazard identification has, particularly when operating at low-level, and how distractions can impact operations. It is a reminder that distractions are not unique to any one type of operation and that no pilot is immune.
AO-2011-107: VH-NIW, Wirestrike
Date and time: 26 August 2011, 1545 WST
Location: 5 km N of Mogumber, Western Australia
Occurrence category: Accident
Occurrence type: Wirestrike
Aircraft registration: VH-NIW
Aircraft manufacturer and model: Air Tractor Inc. AT-802
Type of operation: Aerial work
Persons on board: Crew – 1 Passengers – Nil
Injuries: Crew – 0 Passengers – Nil
Damage to aircraft: Serious