Ayres Corp S2R-T34, VH-OCR, 8 km SE Yenda, NSW, 29 September 1997

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.

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.

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 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.