All About Backshells in Aviation

Perhaps no other vehicle is exposed to the elements more than airplanes, requiring every component to be protected and secure. Of the various systems on an aircraft, there is arguably none more vulnerable than the electrical system.

At the most basic level, a backshell is a component used to protect and support the cabling in an aircraft's electrical system. Backshells are classified by many part catalogs as "connector accessories" because they are placed concurrently with circular connectors. Typically, backshells are used together with other protective components to further guard vulnerable areas from corrosion and wear. Nearly all backshells are made of metal, rubber, or neoprene, depending on the application.

Like any widely used part in aviation, there are particular standards that define the requirements that a backshell must fulfill. Particularly, AS85049 lays out the various functions that a backshell must perform, which include protection from environmental stresses, fluid, mechanical stresses, temperature, and electromagnetic interference. While backshells must effectively protect wiring from each of these conditions separately, there are times when certain protections are not needed. For example, wiring that runs near the engine would require a backshell designed with a higher amount of thermal resistance than a cooler part of the aircraft.

When choosing the correct backshell for any aviation application, there are several important factors that one must consider. The first is the size and shape of the component. Backshells are produced in various sizes depending on the diameter of the associated cable. Additionally, backshells can either follow a straight design or be curved up to 90 degrees, depending on the application. Another consideration is the condition of the intended operating environment. For example, naval aircraft require a more robust, corrosion-resistant backshell when compared to aircraft operating inland. Finally, one must consider the EMI shielding requirements of the electrical system to which the backshell will be installed. With these considerations, one can better understand the several categories of backshells:

Non-Environmental Backshell: This class of backshell provides excellent mechanical resistance but is not equipped with the extra sealing parts required to protect against environmental stressors. As such, non-environmental backshells are most commonly found in temperature-controlled parts of the aircraft.
Environmental Backshell: Designed specifically for harsh operating conditions, environmental backshells provide resistance to moisture and other elements.
Environmental/on-Environmental EMI Backshell: Portions of the electrical system more prone to interference caused by radio and electromagnetic frequency should have EMI backshells installed.

Proper installation and preventative maintenance are important factors in the efficacy and longevity of backshells. Of particular concern is the degree to which the backshell is tightened. In a study performed by the FAA, it was found that loop resistance tracked linearly with the degree to which the backshell was disengaged. Between the constant vibration of flight, the pressure changes caused by altitude, thermal cycling, and general wear on the metal components, it is important for maintenance crews to regularly inspect each backshell connection.

Equally as important as choosing the correct backshell for your application is finding a reliable distributor. At Aviation Domain 360, we offer a wide selection of backshells from the industry's leading manufacturers. Owned and operated by ASAP Semiconductor, we provide customers with competitive pricing and rapid lead-times on over 2 billion components for the aerospace industry. We also offer same-day shipping on qualifying in-stock items, making us the best choice for customers facing aircraft on ground (AOG) situations. Browse our expansive catalog and submit an RFQ today to learn how Aviation Domain 360 revolutionizes the parts purchasing process.