Robinson Helicopter Co R22 ALPHA, VH-UXU

The pilot was probably not aware of the existence of the
powerline hazard.

The helicopter departed from the pad outside the operator's
hanger at Mt Isa aerodrome at 1048 EST. The helicopter tracked west
through the low ridge before detouring south, then turning north to
the stockyards where the pilot landed to board the property
manager. It remained on the ground for approximately 3 minutes
before departing north east to conduct a search on a north west
heading along the North Branch of Spear Creek. From there the
helicopter turned left and tracked south east to a position east of
the ridge. The helicopter then tracked south for approximately 3
km. It then turned right, onto a reciprocal heading, and tracked
north to Spear Creek. It followed the creek north west for a short
distance before turning further left to track south west back to
the stock yards. The helicopter then manoeuvred around the
sockyards before turning and tracking south along the western edge
of the low ridges. The helicopter collided with the powerline, 5.5
km southwest of the aerodrome, at 1113.

It is possible that the pilot may have intended to initially
conduct an inspection flight to locate the missing cattle, however,
after locating the cattle the nature of the flight changed to a
mustering role and safety precautions normally carried out prior to
mustering operations were not taken.

Visual cues, such as power poles, assist in the detection of
wires. In this instance, the poles would have been partially
obscured to the pilot's view by terrain and trees. Additionally,
the angle subtended by the widely spaced poles would have placed
them more towards the pilot's peripheral vision where they would
have been less likely to be noticed.

The only visual cue to the pilot would have been the single-wire
conductor. Even in bright sunlight conditions, a conductor dulled
by oxidation would not have been readily discerned. In order for
the pilot to have seen and avoided the powerline, he needed to be
at the correct focal distance and looking directly at the wire.

Pilots operating at a low height should not rely on being able
to see a powerline in time to take avoiding action.

The pilot and passenger of a Robinson R22 helicopter were
conducting an aerial inspection and cattle mustering flight. During
the flight, cattle were observed outside the fenced area and the
pilot descended the helicopter to direct the cattle back towards
the fence. The passenger then directed the pilot to fly the
helicopter along the eastern fence to check its security. The
passenger reported that the pilot had just commenced to climb
higher, at his request, when the helicopter collided with a
single-wire powerline. Recorded Global Positioning System data
indicated that the helicopter struck the powerline at a speed of 55
kts. The wire did not break and the helicopter pitched nose down.
The main rotor severed the tail boom and the helicopter collided
with the ground 69 m beyond the powerline. It impacted in an
inverted attitude, facing back along its direction of travel and
rolled forward onto its left side. There was no evidence of fire
in-flight or after the impact.

The main rotor, mast and upper right side of the helicopter
cabin took the main impact and the mast was partially driven into
the cabin. The pilot, who occupied the right seat, received fatal
injuries. The passenger, although seriously injured, walked 200 m
to a track and waited almost 2 hours until found by a passing
motorist. The passenger reported that injury prevented him from
picking up and activating the portable Emergency Locator
Transmitter that was ejected from the helicopter cabin.

The powerline supplied electrical power to a nearby property and
was aligned approximately east-west at right angles to the
helicopter's flight path. It spanned a distance in excess of 500m
from a pole in a saddle on a ridge east of the fence, to another
pole set among trees in a timbered paddock. Strike marks on the
wire indicated that the helicopter had struck the powerline at
approximately mid-span. There were no markers on the powerline.
Australian Standards (AS 3891.1-1991) specified markers on
powerlines where the height of a cable exceeded 90m. The powerline
did not exceed that height and at the point of contact was about
20m above ground level (AGL).

The pilot held a current Commercial Pilot Licence (Helicopter)
and was appropriately qualified for cattle mustering operations. He
held a valid Class 1 medical certificate and did not require any
vision correction. An article on the visual aspects of wire
detection by Dr Gordon Cable in the Directorate of Flying
Safety-Australian Defence Force's special wirestrike edition (1997)
of their safety journal "Spotlight" stated that under ideal
conditions, the human eye can resolve detail down to an angle of 30
seconds of arc. That equated to being able to see a 5 mm thick wire
from a distance of 150 m. However, contrast between the wire and
the background against which it is viewed and the medium through
which it is viewed, affect detection. The pilot was wearing a
helmet with tinted visor. The fragments of perspex from the
helicopter's windshield did not show any sign of being scratched or
crazed.

The operator's Operations Manual required pilots to familiarise
themselves with the area to be mustered, including any
obstructions, before commencing mustering operations. Although the
passenger had engaged the operator on previous occasions for the
same work, no map of the area to be mustered was held on the
operator's file. The passenger was aware of the existence of the
powerline and stated that on previous occasions some pilots had him
draw a "mud map" on the ground to indicate the area to be mustered,
including powerline hazards. The pilot had reportedly not asked the
passenger about any powerline hazards prior to the flight. There
was no evidence that the pilot had previously flown over or
inspected the area to determine the presence of hazards.