White Paper – Is it possible to repair fibre-optic cables on an aircraft without removing the whole cable harness?

A Mechanical Splice for On-Platform Repair of Fibre Optics in Harsh Environments

by Andrew Lee, AVoptics Ltd

Introduction

Over the past 10 years the use of fibre optics on aircraft platforms has changed from a sporadic usage to become a fundamental backbone of a modern avionics system.  With the proliferation and use of digital video both inside and outside of airframes coupled with the need for ever more sensors, the use of fibre optics will continue to grow. Most in-flight entertainment systems now operate with fibre optics with several suppliers only offering a fibre optic solution. The lighter weight, wider-bandwidth and faster data rate of fibre-optic cable make them preferable to copper cable equivalents. They also have the added advantage of being free of electro-magnetic interference (EMI) and are intrinsically safe in fuel systems or other volatile environments.

The use of fibre optics in harsh environments is increasing significantly, with the technology being placed in ever more severe conditions. Platforms such as A380, A350,787 and Gulfstream G650 all have optical networks on board. With the ETACS system on board the A380 having a single fibre link that runs the length of the aircraft. Aside from the aerospace industry fibre optic systems have also been growing in vehicles, armored systems, rail, oil and gas and space markets. A prime example is on the new General Dynamics AJAX armored fighting vehicle which has an extensive fibre optic network to deliver many of the key mission elements.

Traditionally one of the barriers to the acceptance of this technology has been the supportability of fibre optic technology when compared to its copper counterpart. Whilst the support for the early point to point fibre optic systems could be managed with a remove and replace philosophy the more modern integrated systems need a different approach. Support of these systems urgently needs a fibre optic splice repair, but this requirement has not been met, until now.

The Problem

In aerospace fibre-optic cable installations, repair systems exist for re-terminating damaged connectors but there is currently no known solution for repairing damage which occurs in the middle of a loom. In current practice in rugged applications, when a break occurs in the middle of the loom it cannot be fixed without removing the whole cable run for replacement. This is both costly and time consuming.

If loom damage does occur, the current strategy is to remove and replace the whole loom, estimated to cost £10,000 parts and to need 3 days elapsed time and significant hands-on labor time. There is also a greater risk of damaging other parts of the system while it is being replaced.

 

The image in figure 2 shows an example of a connector from an avionics communications system.

In order to replace a cable, this connector would need to be fully dismantled and reassembled inside the avionics bay, which is a time-consuming and difficult operation. These options often require removing a host of other equipment and panels to access all parts of the loom/cable being replaced.

The Requirement

The industry needs an inline splice that can reinstate a damaged fibre-optic cable to a fully mechanical-integrity repair with high optical performance. The solution needs to use existing tooling and training and should be successfully implemented in less than two hours. The solution should not require the disassembling of connectors or backshells on the system, protecting the cable harness from the risk of further damage.

The Solution

AVoptics have used their extensive knowledge of fibre optic issues and have developed a splice to fulfil these requirements. An example can be seen in figure 3. The solution is a mechanical splice that robustly and securely terminates the optical fibre, as well as the strength member, buffers and outer jacket. The splice is designed to be installable with an existing AVoptics repair kit.

 

Results from Trial Installation

A trial was performed on and RAF aircraft. Two optical fibers were deliberately broken and then repaired using the splice.

The trial was successful with both repairs being performed in-situ restoring the links on the aircraft. Different operators recorded their repair times which ranged from only 15 – 20minutes. The saving in cost and time is substantial.

The maximum recorded insertion loss of splice 0.55dB, typical 0.25dB. Extensive testing was conducted to review overall mechanical strength and retention of epoxy before curing was performed. Full physical integrity was maintained, resulting in a Pull Force greater than 125 Newtons.

 

 

Conclusion

Based on the results of the initial testing and feedback, a small number of modifications were made to the splice to improve the design (Figure 4 shows current, new design).

Overall, the splice has performed very well in testing and has the potential of saving an average of approximately £6,000 per repair. It also has the potential to significantly improve aircraft availability when a fibre optic issue arises.

The splice has proven its capability and has demonstrated that a cable can be repaired and returned to full performance, with the optical and mechanical integrity of the cable preserved. It is now recommended by the UK MOD Air Commodities Teams as a viable means of reducing aircraft down-time and repair costs.

The AVliteSplice is now in full volume production, and available to assist in your on-platform fibre-optic cable and harness repairs.

Do you want to know more?

After reading this article, do you have questions about repairing fibre-optic cables on an aircraft or other platforms?  If so, contact AVoptics today to have your questions answered and receive more information about this innovative solution.

It is in all of our interests to work together to keep aircraft maintenance efficient and affordable.

Click here for details:  https://www.avoptics.com/product/avlitesplice/

or call +44(0)1935 471606 or email info@avoptics.com

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