The aircraft took off from a private airstrip on Farm 1303 at Whitton NSW on a flight to spray chemical on two paddocks at Farm 2339, Dalton Road, Yenda. Eyewitnesses reported watching the aircraft spray the first paddock using north-south oriented runs. When the first paddock was completed, the pilot commenced spraying the second using east-west oriented runs, starting at the northern end of the paddock. After making several spray runs, the pilot finished a run heading in an easterly direction. He pulled the aircraft up and commenced a right procedure turn to line up for the next run in a westerly direction. While lining up for this run, the left wingtip struck the upper branches of a large dead tree which was located close to the boundary of the paddock being sprayed. The point of impact was approximately 0.5 m inboard of the left wingtip. A piece of branch, 200 mm in diameter, broke off the tree. The left wingtip and several small pieces of wing material separated from the aircraft at impact.
Eyewitnesses reported that the aircraft immediately rolled to the left and impacted the ground inverted. The aircraft slid along the ground before coming to rest inverted. The aircraft did not catch fire but was destroyed by impact forces. The pilot received fatal injuries. Witnesses advised that the weather conditions at the time of the accident were clear skies and light winds. Being late afternoon, the sun was visible in the western sky.
Examination of the accident site revealed that the aircraft had struck branches about 20 m above ground level with its left wingtip. The wingtip and several pieces of the wing landed up to 180 m west of the tree. Ground scars indicated that the aircraft impacted the ground inverted. The fuselage, wings and empennage remained relatively intact and were located approximately 41 m south of the initial ground-impact marks. Propeller slash marks indicated that the engine was producing power at ground impact. The cockpit truss had separated from the fuselage and was located about 22 m from the aircraft's final resting position. The ailerons were jammed in the neutral position.
Examination of the wreckage did not reveal any pre-existing defects or malfunctions that would have precluded other than normal operation. An inspection of the maintenance records showed that all required maintenance had been completed.
The pilot was the holder of a commercial pilot licence and was appropriately qualified for the flight. He had held a Grade 1 agricultural rating since 11 September 1985 and had flown 14,816 hours. At the time of the accident, the aircraft's calculated weight was 2,876 kg, less than the maximum weight authorised for agricultural operations of 3,042 kg. The aircraft's calculated centre of gravity was within limits.
The aircraft was fitted with a Satloc navigation system, which provided the pilot with guidance commands to fly accurate spray patterns. The guidance indications were displayed on a light bar which was mounted on top of the fuselage in front of the aircraft windscreen. The display was approximately 1 m in front of the pilot's eyes. Witnesses suggested that the pilot normally used the Satloc system and its light bar indicator during spraying operations.
Manoeuvring the aircraft to commence the next swath run was a high workload period for the pilot, requiring precise flying to position the aircraft accurately in both lateral and vertical planes. As the pilot was lining the aircraft up to conduct a swath run in a westerly direction in the late afternoon, the sunlight coming through the windscreen would have created glare in the pilot's field of vision, partly obscuring the tree. When using the Satloc system's light bar indicator to align the aircraft with the line of the next swath run, the pilot's vision would have been focussed, for at least some of the time, on the light bar. When the pilot's eyes were focussed on the light bar, more distant objects, such as the tree, would not have been in focus and would therefore have been harder to see. Although the pilot must have been aware of the tree's presence, the high workload, the glare from the setting sun and the pilot focussing on the light bar indicator all contributed to the pilot temporarily being unaware that the tree infringed his intended flightpath.
The damage to the left wing when it struck the tree would have resulted in a loss of lift and an increase in drag from this wing. This would have caused the aircraft to roll rapidly to the left and, as the ailerons had jammed, the pilot would have been unable to stop the roll. Thus, after impact with the tree, the aircraft was most likely uncontrollable.
When the cockpit truss was tom from the aircraft, the space remaining between the ground and the pilot's seat was too small for the accident to have been survivable.
The following factors were determined to have contributed to the accident:
- The glare of the sun shining through the aircraft's windscreen may have partly obscured the tree from the pilot's field of vision.
- The use of the Satloc light bar indicator may have resulted in the pilot focussing his eyes, for at least some of the time, on a close object causing distant objects, such as the tree, to be out of focus and thus more difficult to see.
- The failure of the cockpit truss to remain in position when the aircraft struck the ground inverted made the accident unsurvivable.
As a result of this occurrence, the Bureau of Air Safety Investigation is assessing safety issues related to the following:
- the design and use of the GPS "light-bar" used in agricultural operations; and
- the overturn protection provided in two-place Ayres Thrush aircraft.
|Date:||29 September 1997||Investigation status:||Completed|
|Time:||1815 hours EST|
|Location:||8 km SE Yenda|
|State:||New South Wales||Occurrence type:||Collision with terrain|
|Release date:||01 November 1998||Occurrence category:||Accident|
|Report status:||Final||Highest injury level:||Fatal|
|Aircraft manufacturer||Ayres Corporation|
|Type of operation||Aerial Work|
|Damage to aircraft||Destroyed|
|Departure point||Farm 1303, Whitton NSW|
|Departure time||1710 hours EST|
|Destination||Farm 1303, Whitton NSW|
|Role||Class of licence||Hours on type||Hours total|