Important notice: cargo hook attachment failure

Important notice: cargo hook attachment failure

A recent cargo hook attachment failure on a turbine helicopter highlighted the risk of using a fertilizer bucket on a cargo hook fitted with a load cell weighing system.

This failure is the fourth New Zealand hook attachment failure that we are aware of.
 
The torque reaction that occurs when the fertilizer bucket slide opens, dumping the fertilizer into a high-speed impellor, causes high stress on the cargo hook and attachment fittings.

Many weigh system load cell links are sensitive to these forces which leads to a fatigue failure quicker than other parts in the cargo hook installation.

If you have an early style R44 cargo hook attachment it will be prone to this problem. If you have an upgraded cargo hook suspension, this problem will be mitigated.
 
A failure of the hook attachment can cause a considerable amount of damage including the destruction of the fertilizer bucket or other loads. This type of fatigue damage is invisible, so monitoring an approaching failure is not possible.
 
Rigging a fertilizer bucket slide so that it will open and close fast aggravates these destructive torque forces.
 
Our recommendations
We recommend that fertilizer buckets do not get used in conjunction with a link-style weigh system load cell. We have developed a swivel assembly that has electric and air channels that may assist, reducing the risk of failure.

If you have any concerns or questions, please do not hesitate to contact us.

Posted: Wed 19 Nov 2014

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PO Box 372, Taupo
Ph: +64 7 378 8688 | Fax: +64 7 378 0692
rotorandwing@xtra.co.nz