Sequence of events1
On 6 December 2005, the owner-pilot of a single-engine Cessna
Aircraft Company 150G, registered VH-KPQ, was conducting aerial
mustering operations on a family owned station, 156 km north of
Broken Hill, NSW. The pilot, who was the sole occupant, had
departed a station airstrip at about 0710 Eastern Daylight-saving
Time to coordinate the movement of sheep from an 18,000 acre
paddock to shearing shed yards near the homestead. The paddock had
medium to dense coverage of 2.5 m high scrub and was generally
flat. Aerial mustering activity that day involved flying a north to
south pattern progressively from the east to the west and directing
ground-based mustering personnel to the location of the sheep.
Those personnel were using two motorbikes and a four wheel drive
vehicle in the muster. All of the musterers were communicating with
ultra high frequency (UHF) radio.
At about 0835, the four wheel drive vehicle was being used to
move a few sheep along when the driver lost sight of them. The
driver advised the pilot by UHF radio and shortly after the
aircraft circled above the area a number of times at about 250 ft
above ground level (AGL), but the pilot was reported to have not
seen the sheep. The driver then sighted the sheep in thick scrub
that the vehicle was unable to penetrate, and advised the pilot of
the situation. The pilot requested that the driver reverse and
drive onto a nearby track. The driver asked the pilot to report
when the sheep moved away from the scrub. There was no response.
Shortly after the driver noticed smoke nearby and found that the
aircraft had impacted the ground and there was an intense fire. The
pilot was fatally injured.
The other musterers were in different areas of the paddock and
did not observe the aircraft's descent and impact with the ground.
No one heard an emergency radio broadcast from the pilot. One of
the musterers observed the pilot's takeoff from the station
airstrip and heard the engine a number of times during the
mustering before the accident, and reported that it sounded
normal.
Wreckage and site information
The aircraft wreckage was found approximately 400 m to the
south-east from where the mustering vehicle was operating. The
aircraft was upright with evidence of severe impact damage to the
left wing, nose section and rear fuselage. There was evidence of
intense fuel-fed fire damage to the cabin area and left wing. The
main wreckage, approximately 8 m from the first ground impact mark,
contained all the aircraft parts except for the nosewheel, which
was found nearby.
The ground impact marks and damage to the left wing indicated that
the initial impact with the ground was the outer leading edge of
the left wing. In addition, the minimal damage to the shrubs
surrounding the initial ground impact marks indicated that the
aircraft impacted the ground with a steep left angle of bank
between 70 and 80 degrees. The damage to the wing, and the nose
impact position also indicated that the aircraft impacted in a nose
down attitude with a high descent rate. There was no evidence of
rotation.
Examination of the aircraft, including the flight control
systems and engine, did not reveal any evidence of pre-impact
defects. Damage to the propeller indicated that the engine was
operating at ground impact. The wing flaps were found in the
retracted position.
Pilot information
The pilot commenced flight training in 1987 and flew 18 hours in
a Cessna 150 and 32 hours in a Cessna 172. The pilot purchased a
Cessna 206 and completed his flight training in that aircraft. He
was issued with a private pilot (Aeroplane) licence in 1988. There
was no evidence of any low level or aerial stock mustering
permission (the relevant regulations are outlined below).
Family members reported that the pilot used the Cessna 206
primarily for aerial mustering on pastoral properties that he owned
in regional NSW. About 18 months prior to the accident, the pilot
purchased the station north of Broken Hill and in August 2004,
purchased the Cessna 150 primarily for mustering on that
station.
The pilot's logbook was full and did not contain any entries
after 1 October 2004. He had logged 36.5 hours flying the Cessna
150 over the station north of Broken Hill and a total of 2,041
hours. Although there were no flights logged by the pilot after 1
October 2004, family members reported that the pilot continued to
fly the Cessna 206 and the Cessna 150 after that date.
The pilot's most recent flight review was competed on 24 April
2004 in his Cessna 206. The instructor who conducted the review
reported that the pilot was competent and that the review had
included steep turns and stall recovery. Steep turns were practiced
at 3,000 ft AGL and between 45 and 60 degrees angle of bank. Stall
recovery was practiced at 3,000 ft AGL and included recovery from a
stall during a steep climbing turn with low power.
The pilot's logbook indicated that the pilot had completed stall
and steep turn training in a Cessna 150 during his initial training
in 1987/1988. There was no record of any stalls or steep turn
training in a Cessna 150 since.
The Civil Aviation Safety Authority (CASA) issued the pilot with
a Class 2 Medical Certificate on 30 June 2004 that was valid to 30
June 2006. That certificate contained a restriction requiring the
pilot to wear distance vision correction and to have reading
correction available during flight.
The pilot had been involved in mustering activities that
included about two hours aerial mustering in the Cessna 150 per day
during the previous two weeks. Two days before the accident the
pilot did some aerial mustering in the Cessna 150 and then flew the
Cessna 206 to a station in the Hay area. He was reported to have
worked on the station until about 2030, before going to bed at
2300. The next morning the pilot awoke at 0600 and departed at 0830
for Wagga Wagga aerodrome, landing at 1000. At 1500, the pilot
departed for the station north of Broken Hill via Hay and Broken
Hill, arriving home at about 2000. The pilot worked in the sheep
yards until returning to the homestead at 2130. Family members
reported that the pilot was tired and had a sore shoulder for which
he took a non-prescription painkiller. He retired to bed shortly
after.
On the day of the accident, the pilot woke at about 0615 and at
about 0630 flew the Cessna 206 from the airstrip near the homestead
to another station airstrip where the Cessna 150 was hangared. It
was reported that he was in good spirits and appeared well
rested.
At the time of writing this report, the post mortem report was
not available. There was no evidence of any physiological condition
that may have contributed to the accident.
Aircraft information
The Cessna 150G was a two-seat, high wing aircraft equipped with
a Continental O-200A engine rated at 100 HP (74.6 kW). The aircraft
was fitted with a pneumatic aural stall warning system that
activated 4 to 8 kts before the stall was reached. That was the
only aural warning known to be fitted to the aircraft.
The pilot operated the Cessna 150 on a mixture of 10% aviation
gasoline (Avgas) and 90% unleaded automotive petrol as authorised
by a flight manual supplement. The flight manual supplement stated
that when using automotive fuel, the onset of carburettor ice may
occur earlier than with Avgas under the same atmospheric
conditions. Two days before the accident, the aircraft fuel tanks
were reportedly filled from clean drum stock in the hangar using a
hand-pump that included an in-line filter. On the morning of the
accident, the pilot was observed conducting his pre-flight checks,
including of the aircraft's fuel system drains.
In addition to the aviation radios, a UHF transceiver was fitted
to the aircraft for use during mustering operations. The audio
output from that transceiver was wired into the aircraft's phones
jack, and there was a hand microphone. The pilot was reported to
use an aviation headset.
The pilot's Cessna 206 was a six-seat high wing aircraft
equipped with a Continental IO-520F engine rated at 300 HP (223.7
kW).
Meteorological information
The applicable aviation area forecast was valid from 0800 and
predicted isolated showers and thunderstorms with broken
2 cloud at 10,000 ft. The wind at 2,000 ft was expected
to be from the north-west at 20 kts. Turbulence was forecast to be
moderate in the broken cloud and after 1200, light to moderate
below 9,000 ft.
Automatic weather observations at 0830 from the nearest Bureau
of Meteorology (BoM) site at Broken Hill recorded scattered cloud
at 9,500 ft and a surface wind from the south-west at 10 kts. The
temperature was 26 degrees, the dewpoint was 14 degrees and the
barometric pressure was 1003 hPa. There was a report of a
thunderstorm and 0.2 mm precipitation between 0730 and 0800. The
BoM advised that the Broken Hill observations were representative
of the weather conditions at the accident site.
One of the ground-based musterers reported that at the time of
the accident, the wind was a light south-westerly and it was
overcast and humid.
The 0830 Broken Hill temperature and dewpoint depression3 was plotted on a Carburettor icing -
probability chart. That chart predicted moderate icing at
cruise power, or serious icing at descent power in those
conditions.
Current regulations
Civil Aviation Order 29.10 defines aerial stock mustering as
'the use of aircraft to locate, direct and concentrate livestock
whilst flying below 500 feet above ground level'. The aeronautical
experience requirements for a pilot to engage in mustering
operations include that the pilot must complete 5 hours low flying
training and an exam to confirm pilot proficiency, followed by 10
hours operational training. That training included:
- level, climbing and descending turns and recovery from the
stall at up to 60 degrees angle of bank - slow flying and the methods of losing height at low level
- steep climbing and descending turns away from, and returning to
a ground reference.
Aerial stock mustering
Aerial mustering of stock in aeroplanes such as the Cessna 150
usually involves low-level flight including steep turns at low
airspeed to allow the pilot to monitor the location and movement of
stock, and to guide ground-based personnel accordingly. It was
reported that the pilot usually conducted aerial mustering at an
estimated height of between 150 and 200 ft AGL, but if sheep found
cover in dense scrub, the pilot would sometimes fly lower and apply
power over the sheep to encourage them to move.
Turns are a significant risk during aerial mustering in
aeroplanes due to the reduction in vertical lift component and
significant increase in stall speed4
with bank angles over 60 degrees. To maintain height in a turn at a
constant airspeed requires an increase in lift, which produces an
increase in drag that necessitates an increase in engine power.
Depending on the angle of bank and the conditions, maximum engine
power may not be sufficient to prevent a descent.
The use of small angles of flap reduces the stall speed and
lowers the nose angle for a particular airspeed. Although one
low-level flying expert indicated that use of flap was advantageous
during low speed turns, opinion amongst pilots with experience in
low-level operations regarding the use of flap during those
operations varied.
One of the ground-based musterers reported that he heard a
buzzer twice in the background of some of the pilot's UHF radio
transmissions. That included while the aircraft was circling
shortly before the accident. He also reported hearing the same
buzzer during the pilot's previous mustering operations. An
experienced aeroplane mustering pilot and instructor reported that
it was common for the stall warning to activate in the steeply
banked turns used during aerial mustering operations.
A number of potential sensory illusions can result in mustering
pilots inadvertently applying excessive bank angles during turns.
If a pilot's head is orientated into a turn (such as looking at the
ground or stock) and is then quickly rotated away, the pilot's
vestibular balance system can produce a sensation that the aircraft
is underbanked. A visual illusion that the aircraft is skidding out
of a turn can occur when turning from downwind to upwind while
looking at the ground, also giving the sensation that the aircraft
is underbanked.
When pilots are paying very close attention to stock by moving
their head during a turn, they may tend to move the flight controls
in sympathy with head-body movement. This can lead to inadvertent
overbanking. Distractions during a turn, such as looking for stock
or using a radio, can also increase the risk of inadvertently
steepening the turn and/or allowing the airspeed to decay.
- Only those investigation areas
identified by the headings and sub headings were considered to be
relevant to the circumstances of the occurrence. - Five to seven eighths of the sky
obscured by cloud. - Dew point depression is calculated
by subtracting the dewpoint from the ambient temperature. - Stall speed is the airspeed at which
the stalling angle of attack (angle between effective wing chord
line and relative airflow) occurs resulting in rapid decrease in
lift