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Helicopter Accident Linked to Flashover from High Voltage Lines

March 14, 2012 Leave a comment

Hong Kong (HKSAR) – In accordance with the Hong Kong Civil Aviation (Investigation of Accidents) Regulations (Cap. 448 sub. leg.B), an inspector’s investigation is in progress to determine the circumstances and causes of the accident involving an Aerospatiale SA 315B LAMA helicopter (registration mark B-HJV) operated by Heliservices (Hong Kong) Limited in Kau Lung Hang Lo Wai, Fanling, on January 3, 2011.

The investigation team today (March 9) released Accident Bulletin 2/2012 as an update to Accident Bulletin 3/2011 issued on February 1, 2011.

A spokesman from the Civil Aviation Department (CAD) said that the objective of the investigation is to determine the circumstances and causes of the accident with a view to preventing accidents and preserving life in the future. The updated bulletin contains information relating to the accident as determined up to the time of issue and must be regarded as tentative.

“The latest findings indicated that at the time of the accident, the helicopter longline might have come close enough to the nearby overhead high-voltage electricity line conductor to trigger a fault current to flow from the line conductor to an earthed object, causing a flashover,” he said.

“A series of high-voltage electrical experiments were conducted in a suitably equipped laboratory to evaluate the possible scenarios. Results have revealed that if the accident longline, which was shrouded by a protective nylon fabric jacket, had moved to a distance closer than approximately 20 centimetres to the overhead line conductor and an earthed object, the air insulation gap between them could break down and a flashover could occur.”

The spokesman added, “The investigation team has issued one recommendation to Heliservices (Hong Kong) Limited at the current stage, which is to suspend the use of any underslung cable assemblies on Aerospatiale SA 315B LAMA helicopters, which consist of electrical conducting material, in the vicinity of overhead high-voltage electricity lines until completion of the investigation.

The investigation team will continue to study all other relevant evidence and information, including but not limited to the operational and management aspects of the helicopter underslung operation, in order to determine the circumstances of the accident.”

The full Accident Bulletin 2/2012 is attached in the Annex. It is also available for download at the CAD webpage (