Fluid Susceptibility and Waterproofness
As a second installment of our deep dive into the RTCA DO-160 requirements, we now shift our focus to the liquid phase of our environmental conditions. Airborne equipment constantly encounters different liquids, whether through nature's mechanisms like rain and condensation or human interactions involving man-made chemicals. Examples of such airborne equipment would be seats (including Power Supply Unit/Passenger Control Units), interior furniture (i.e. honeycomb panels, metallic finishes, composites), avionic sensors (excluding hermetically sealed packages), landing gears, and exterior panels/seals. Exposure to different liquids has the potential to compromise molecular integrity, hindering the equipment’s ability to function as their design originally intended. Sections 10 and 11 of DO-160, Waterproofness and Fluid Susceptibility, provide procedures that test the equipment’s ability to withstand exposure from water as well as other chemicals pertinent to its maintenance and operation. These requirements enable the aerospace industry to ensure the proper operations of mechanical and avionics components regardless of the environmental conditions and
contaminants they may encounter.
Waterproofness, as detailed in Section 10, lays out the standards that components must meet the requirements to withstand condensation, drips, sprays, or continuous water exposure. As one of the most prevalent molecules on Earth, H2O has a knack for infiltrating even the tiniest crevices, some of which must remain corrosion-free—a condition often referred to as the silent enemy of aircraft. Corrosion can compromise the integrity of metals and alloys, leading to structural failures in various applications. In addition, corrosion significantly reduces the lifespan of metal components and structures by accelerating wear and tear. The addition of water and humidity can also lead to electrical malfunctions, material decay, and even unwanted organic growth. Not only can exposure to wet and highly humid environments affect the overall performance of exterior materials, but interior components are also susceptible to deterioration that could affect their safety performance. When various temperature conditions are incorporated into the equation, as discussed in our part 1, the impact of this exposure can become magnified. For example, colder temperatures can lead to freezing expansions that may cause fractures in materials which leave them susceptible to water breaches. Alternatively, higher temperatures can cause the material itself to expand which could leave unwanted gaps that water can infiltrate.
Section 11 encompasses a broader spectrum of fluids that avionic equipment might encounter, whether in the form of spray or immersion. Fluids intended for human consumption, fuel systems, or hydraulic systems introduce additional complexities that must be taken into account during the design process. For example, exterior components such as landing gears and exterior panels of the aircraft are tested for de-icing fluids, fuel, or hydraulic fluids. Similarly, seats and various panel samples of the galley materials are often tested for coffee and soda exposure. Fluids that possess differing properties such as acidity, viscosity, or temperature all contribute to interaction that occurs between a fluid and a material it is exposed to. If not accounted for, it is possible to cause a degradation of quality due to staining various surface effects upon the material. In harsher conditions, it’s possible for certain fluids to cause material decay which can lead to problems with structural integrity or assembly functionality. Considering potential exposure to contaminants based on the location of each piece of equipment should be of the utmost importance in the material selection, as it is critical for proper operation. For a detailed list of fluids and their temperature exposure requirements, please refer to table 11-1 from RTCA-DO160.
During the design process it is crucial to take into account both the waterproofing aspect and the potential effects of different fluids on avionic equipment. A more comprehensive evaluation of avionic equipment performance can be achieved by subjecting it to testing procedures that mimic real world conditions. Our proficient team and well-equipped laboratories are primed to furnish quality data, which can aid in refining designs during the material selection or certification phases. For more information on our DO-160 testing services, please contact David.Suazo@mgaresearch.com