Powerline markings and aerodrome information.
The aircraft, a PA 38-112 Tomahawk, was on final approach for a
landing at Torquay (Vic.) ALA when it struck powerlines. The
aircraft suffered significant damage from the powerlines and
further damage from the impact with the ground. The pilot and his
passenger (also a pilot) were not harmed.
THE POWERLINES: The aircraft collided with two strands of 3 X 12
gauge (2.75-mm) galvanised steel powerlines, grey in colour. The
pole height was 12 m and the line dropped to 6.55 m above ground
level at its lowest point. The line ran perpendicular to the runway
direction, a short distance outside the fence marking the end of
the runway surface. The line was marked by orange marine buoys of
200-mm diameter that had faded on the upper surface to a dull
white. This combination of grey powerlines and faded markers made
the lines virtually indistinguishable from the dry, light brown
surface, especially in the prevailing bright but overcast
conditions. The electricity company had conducted a ground
inspection of the markers every 3 years but had no requirement to
check the upper surface for fading. At the time of the accident the
markers had been installed for approximately 8 years.
Many aerodromes and landing areas around Australia are situated
near buildings or homesteads, and many of these have power supplied
to them by overhead powerlines. Many of these lines have been
marked prior to the publishing of the relevant standard in 1991,
hence a wide variety of markings have been used, many of which are
not effective in ensuring clear visibility from the air.
Australian Standard 3891.1 recommends that any powerlines which
infringe the transitional slope or the approach and take-off slope
of an aerodrome shall be marked by a minimum of three spherical
markers of at least 600-mm diameter placed less than 30 m apart.
One of the markers should be off- white and the other colours
should be chosen to provide maximum contrast with the ground. The
other recommended colours are canary yellow and signal red, with
international orange available for circumstances requiring an
unusual contrast. The markers should also be made of a material
that is resistant to deterioration caused by ultraviolet light. The
document containing the full details of this standard is available
from Standards Australia. Comparing the installed markers with the
Australian standard, the marine buoys installed were a third of the
diameter required and they had lost their colour on the upper
There is a good chance that this accident would not have occurred
had the powerlines been marked to meet the Australian standard. If
the standard had been followed there would have been at least three
markers on the line, each of which presented over eight times more
visible surface than the installed markers. In addition, the
brightly coloured material would have provided a strong contrast
with the background.
AERODROME MARKINGS: The Torquay airport operator had placed
displaced landing threshold markers some way into the runway 18
strip to establish a safe approach gradient over the powerlines.
These markers were painted white, as were the runway edge markers,
which extended the full length of the runway surface. The colouring
of the airfield surface, at the end of a hot dry summer, did not
provide adequate contrast to allow the pilot to see the white
landing threshold markers against the dry grassed surface of the
runway. The aerodrome was marked correctly, however, the local dry
conditions contributed to the accident by preventing easy
identification of the displaced threshold.
AERODROME INFORMATION: The Aircraft Owners and Pilots Association
(AOPA) Airfield Directory contains information supplied by the
aerodrome operator on a survey form supplied by AOPA. That survey
form does not follow the example on page 55 of the Airservices
Australia publication, the Enroute Supplement Australia, in that it
does not list any examples of hazards that need to be considered.
An airport owner may not consider relevant or cover all the hazards
associated with the aerodrome unless there was a list for
reference. The information published for Torquay did not mention
powerlines or any displaced landing thresholds.
Before departing for Torquay the pilot had studied the AOPA
airfield directory and phoned the operator for approval to land. He
also asked about local conditions and was informed of parachute
operations that day. The pilot did not ask, nor was he told about
any powerlines or displaced thresholds. The pilot and his passenger
were familiar with the runway layout having flown over the
aerodrome previously, however neither had landed at the aerodrome.
Approaching Torquay they had heard another aircraft broadcast that
it was landing on runway 18 so they joined crosswind for that
runway, noting as they flew overhead the worn take-off threshold
area adjacent to the fence.
The pilot followed the correct procedure by telephoning the airport
prior to departure, however when questioned later by the
investigator, the operator advised that he had not brought the
powerline or the displaced threshold to the attention of the pilot.
Also, the operator later advised that the correct details and a
diagram could be found in the other private airfield directory, the
Country Airstrips Guide. He did not check which guide the pilot was
- Power lines in the vicinity of some aerodromes and landing areas
are not adequately marked.
- Under some conditions, aerodrome colouring can make runway
markers difficult to distinguish, particularly if the pilot is
unaware of any displaced thresholds.