Lighter and smaller!
In an industry like aviation where weight and space saving are top priorities, these two advantages alone should be enough to convince designers to replace most of the conventional copper wires with fibre optics. Ground communication networks started to make theses change decades ago, so why is it taking so long to see these changes in the aviation industry?
The first thing you’ll probably say is; “well, because of the never-ending certification processes of aviation.” Right? Well, what about other technologies? What about composite materials, touch-screen technology, lithium-ion batteries, Wi-Fi internet and Force Feedback Side-sticks, to name just a few? Each of these “new” technologies had to go through the same certification process. So, what is the problem with fibre optics?
Before going any further, let me clarify one point; fibre-optic cables are already used in the aviation industry, however, there are so few in an aircraft that we can almost say that this technology is mainly rare or not at all implemented. One of the exceptions is the Boeing 777 that has had an extensive fibre-optic network for its in-flight entertainment system since 1995. The use of fibre optics is, however, limited to non-essential systems. The military has started using fibre optics for more essential systems, for example in the Lockheed Martin F-22 and F-35, and in the Eurofighter Typhoon. Yet, their use is limited to mission-critical systems and not flight-critical systems.
The most surprising thing about this technology is the numerous advantages gained from implementing it:
Replacing multiple copper wires with a single fibre
Lighter and smaller cables
It is not affected by EMI (Electromagnetic Interference)
No grounding or short concerns
Upgradeable without ripping out and replacing cable harnesses
So Why Isn’t It Used More?
The main problem when it comes to replacing electronic links with fibre optics is its reliability, particularly in harsh conditions, such as the aircraft operating environment. An aircraft has a number of stresses which do not exist in telecom installations. The temperature extremes and thermal shocks are far greater in an aircraft than in a static installation. Moreover, the mechanical vibration and shock seen in an aircraft are not present in static outdoor environments. Finally, critical systems in aviation demand a much higher reliability than a telecom link, which does not result in an emergency when a connection is lost.
So, the main reason for the slow integration of fibre optics in aviation is its reliability in harsh environments. Recent developments in fibre-optic technology have already pretty much resolved this issue. Its mechanical robustness has been improved, as well as its environmental stability and installation flexibility. Boeing performed fibre optics testing on the 757 platform, mounting the fibre on the landing gear axle and on the engine’s firewall. Initially, the fibre was intended to stay on board for one year, but due to availability of the aircraft, the fibre ended up staying on the plane for four years without a single fibre optics failure.
There is also the fact that aircraft connectors need to be disconnected and reconnected much more often for testing, part replacement, troubleshooting and many other reasons. Since the surface of the fibre has to be perfect in every single way to prevent loss, the wear caused by multiple disconnections over time could create issues on aging aircraft. Therefore, non-physical contact connectors should be used in aviation to prevent these problems.
Another issue with fibre optics is maintenance. It is much harder to repair than a conventional copper wire. First, you have to locate the damaged area, which is done using special testers, such as a Visual Fault Locator or an Optical Time Domain Reflectometer. Then you have to repair it with special techniques and tools using a splice or a pigtail assembly. However, this is still feasible, it simply requires specific equipment and skills that can be taught to any good avionics technician, and a little more time.
To sum up, although the integration of fibre-optic technology in aircraft is slow, it is happening. This technology has so many advantages that investing to resolve its issues is definitely worth it. We often hear people ask; “Is fibre going to make copper obsolete?” It isn’t! The two will coexist, each being employed where it makes the most sense.
What About Going Wireless?
Also, the foreseeable move to wireless technology is often ignored in this debate. Replacing some of the copper wires with fibre-optic cables would significantly reduce the weight of the aircraft and the size of harnesses, there is no doubt about it. But replacing these exact same wires with a wireless connection, in other words, using no wires, is even more attractive. So, why should a company invest in developing technology that might soon become outdated?
No matter what your thoughts are, there are two clear trends regarding aircraft wiring and data transmission in the avionics market; 1) constantly increasing data transmission speeds and, 2) the need to reduce weight. Fibre-optic technology has perhaps had a slow start in the aviation industry, but it still has a bright future. I would not be surprised to see the next generation of avionics architecture using a mix of copper wire, fibre optics and wireless connections, each being used where most appropriate. What do you think?