The average passenger aircraft has upwards of 1,000 various aircraft cable bundles installed within its structure. The wiring and cable assemblies serve integral tasks including flight control, data bus, fireproof redundancy, and more. Two of those cable systems that are imperative to avionics are flight control cables and data bus cables.
Flight control systems manage a variety of monitoring and actuating tasks. These cables stretch from the cockpit to control surfaces within the airframe. They are typically stainless-steel wiring bundles that are coated in a black vinyl casing. Stainless steel is able to withstand greater temperature variations than the mostly aluminum frame of an aircraft but are still affected by the thermal contractions of the airframe.
In order to maintain efficient communication with control surface actuators and remain reliable under the many stressors encountered during a flight cycle, flight control cables are assembled using a pulley system. When a pilot actuates a control, a cable is rotated around the pulleys like a large steel belt. Each system is spring loaded, which helps account for slack that occurs when the aircraft encounters drastic temperature changes.
While flight control cables interact with actuators, data bus cables transmit digital signals between sensors and their corresponding display devices. A standard commercial airplane has 150 to 300 ft. (around 200 km) of this type of cable alone. Data bus cable structure often consist of a shielded “twisted pair” cable that is grounded at each end, and at every junction in the assembly. The most commonly used data bus system in civil aviation is the ARINC 429. Created by Aeronautical Radio Inc., it is the technical avionics standard for data bus cables used in commercial aircraft. This system operates using a double helix wiring, which enables bi-directional transmission to request data and transmit data across a single cable.
Both flight control cables and data bus cables are essential to a pilot for proper monitoring of an aircraft during its flight cycle. As technology advances, it is possible we will see steel wiring replaced with fiber optics technology. The lighter, more reliable, cables have a lower electromagnetic field (EMF) and are notably more affordable. Newer airplanes such as the Airbus A380 and Boeing 787, have already incorporated fiber optic cables into some part of their avionics systems. As older aircraft phase out, it is likely we will see fiber optics technology become the new standard for aircraft cables.