Safety cases to support system modifications

Safety cases to support system modifications

Natasha Fox

WEC specialist engineers were requested by a UK rotary wing client to develop a Safety case for an anti-spin system being developed for a personnel cage suspended below a helicopter.


The project

WEC developed the safety case for an anti-spin system for a personal cage suspended below a helicopter. The client requirement for the cage was driven by the need to suspend engineers to enable them to monitor and perform work on live, over-head, high voltage power lines.

  • Using the guidelines for conducting a Safety Assessment, laid out in the Aerospace Recommended Practice (ARP) 4761, a Functional Hazard Assessment (FHA) identifying the main functions of the system and the associated failure effects was developed and agreed.
  • WEC engineers then performed a full Safety Assessment detailing the findings and conclusions in a written report to the client.
  • The assessment identified a potential problem with the personnel cage emergency release mechanism which could, under certain circumstances, be erroneously triggered as a result of excessive vibration.
  • Following further consultation with the client, the release mechanism was redesigned and the modified system fitted to the installation.
  • In addition, WEC performed Particular Risk and Common Mode Failure analyses together with a Zonal assessment on the anti spin system, which identified further hazards arising from chafing of ropes, Foreign Object Debris (FOD) ingress and fluid contamination.
  • Following recommendations from WEC engineers, further minor changes to the design were embodied and new scheduled, mitigating, maintenance activities implemented on the aircraft and associated equipment.
Woman in hard hat and holding laptop
Man at computer

The benefit

WEC involvement ensured that the bespoke mission system design met the requisite safety standards without significant re-design thus enabling the client to safely continue to maintain their extensive powerline network, without disruption to the power supply network.

Throughout this task, our specialist engineers’ uncompromising commitment to high standards and deep-rooted ability to accurately anticipate both the risk and opportunity in any engineering challenge, enabled us to develop a robust safety case for our client’s ambitious, bespoke mission system design. Put simply, we worked closely with our client to help them build a better product.

Learn more about our Safety Analysis service by calling 0161 482 8508 and speaking to one of our experts.

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