The Cessna 172 was being used to assist a ground party of
station hands to muster sheep on a station property approximately
46 km south-west of Onslow, WA. The manager of the station reported
that the aircraft was being used to spot livestock on the ground
and to muster sheep using a pilot-activated siren on the underside
of the fuselage.
The aircraft was being flown along a generally east-west track,
from one side of the paddock to the other, which gradually
progressed towards the northern boundary. Although members of the
ground party were unable to estimate the height at which the
aircraft was operating, they did report that the aircraft siren was
effective in moving the sheep. An experienced mustering pilot
stated that a siren fitted to an aircraft would probably be quite
ineffective at a height of 500 ft above ground level.
The station manager reported that the pilot appeared to be
attempting to position the aircraft to cut off a mob of sheep that
had broken away from the group he was following. He saw the
aircraft pass approximately overhead and in a westerly direction
before it commenced a left turn.
The manager looked away from the aircraft but reported that he
could clearly hear its engine, which sounded normal. He immediately
looked up when he heard the sound of an impact and saw that the
aircraft had crashed approximately 100-200 m from where he was
standing.
As a result of the accident the pilot sustained fatal injuries
and the aircraft was destroyed. Damage to the aircraft was
consistent with it having impacted the ground in a near vertical
attitude at a low forward speed. A significant quantity of fuel was
later recovered from the aircraft wreckage. There was no evidence
that a mechanical defect had contributed to the accident.
The property owners had employed the pilot to fly their aircraft
to assist with mustering operations. They stated that they had
little knowledge of operating a light aircraft in support of their
primary production activities. One of the owners was aware of a
mustering type endorsement and reported that despite contacting a
number of organisations and authorities, he had experienced
difficulty in finding somebody to conduct mustering training for
the pilot.
The pilot was issued with his private pilot licence (aeroplanes)
on 4 June 1999, 6 weeks before the accident. At the time of the
accident, the pilot had accumulated about 191 hours aeronautical
experience, which included some helicopter training. No evidence
was found to indicate that the pilot had received any formal
low-flying training or that he was qualified to conduct mustering
operations. Investigators were told the pilot had arranged to do
training for a mustering endorsement once he had enough experience
to be endorsed.
Flight and duty time limitations are specified for pilots
engaged in commercial operations. However, as this mustering
operation was being conducted in the private category, there was no
requirement for the pilot or the aircraft operator to comply with
these limitations. Consequently, the pilot was responsible for
determining his daily flying activities. This was done in
conjunction with the property owners, property manager and the
mustering party. Investigators were told that the pilot typically
commenced flying at approximately 0700 local time and continued
through the day, until the last paddock had been completed.
During the course of the investigation the pilot's recent flight
and duty times were reviewed to determine whether fatigue had been
a factor leading to the occurrence. He had flown at least 68 hours
in the 9 days since arriving at the station and had not taken a day
off during this period. On the day of the accident, he had flown at
least 8 hours 30 minutes. He was known to take short breaks from
airborne operations about every 4 hours, during which time he would
refuel the aircraft.