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Recommendation issued to: The Electricity Supply Association of Australia

Recommendation details
Output No: R19970153
Date issued: 13 February 1998
Safety action status:
Background:

SUBJECT

Powerline markings.

OCCURRENCE SUMMARY

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.

ANALYSIS

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 lines 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 did not have a 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 surface.

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.

SAFETY DEFICIENCY

Powerlines in the vicinity of some aerodromes and landing areas are not marked sufficiently to be easily visible in all circumstances.

Output text

That the Electricity Supply Association of Australia give wide distribution to the deficiency highlighted in this report and recommend to its members that they make appropriate use of Australian Standard 3891.1 when marking powerlines.

Initial response
Date issued: 09 April 1998
Response from: The Electricity Supply Association of Australia
Action status: Closed - Accepted
Response text:

I refer to your letter of 13 February and its accompanying report detailing an incident in which an aeroplane struck electricity power lines whilst attempting to land at a Victorian airfield.

The recommendation of the Bureau was that ESAA give wide distribution to the deficiency highlighted in the report and recommend to its members that they make appropriate use of Australian Standard 3891.1 when marking powerlines. ESAA has distributed this report, highlighting the recommendation, to all of its transmission and distribution full member organisations with the request that the report be distributed to all relevant personnel within the organisation. In addition, ESAA's May edition of its publication ESAA News (circulation in excess of 2,000) will also carry a brief report and warning on the incident. Your name and telephone number was given as the contact should any of our members require further information and we advised them to obtain a copy of the Australian standard from. Standards Association of Australia.

 
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Last update 01 April 2011