It is the intent of this document to describe some of the characteristics of the corrosive environment in which U.S. Navy avionic systems and equipment are maintained and operated. This description will provide the equipment design engineers, and interested reliability and maintainability engineers, a general understanding of fleet operational and maintenance environments (both shipboard and shore-based) that are not specifically detailed in a Military Specification, Standard or Handbook, yet are conditions that significantly reduce the reliability of installed avionic equipment.
There is evidence that a major cause of avionic reliability degradation is the result of corrosion, cleanable films, and moisture.1 For purposes of this Design Guide, the acronym C/F/M (Corrosion/Films/Moisture) will be used to describe the compilation of environmentally induced conditions on metallic surfaces. The following definitions are descriptions of each condition:
a. Corrosion - Refers to electrochemical deterioration of a metal through reaction with its environment.
b. Cleanable Films - Refers to films that degrade the operation and function of electrical or electronic elements, such as: unreacted nitrates, sulfates, chlorides, oxides, oily residue and similar cleanable atmospherically deposited films.
c. Moisture-Refers to electrically conductive (ionized) water. Due to the pervasive presence of the chloride ion in the marine environment (both at sea and in coastal regions), it can be assumed that free water is conductive.
This Design Guide is concerned with identifying electrical and associated mechanical design features which affect susceptibility of avionic equipment to C/F/M. U.S. Navy failure documentation will be discussed in order to understand the usefulness of failure data in identifying specific problems attributable to C/F/M. Included is a review of present maintenance procedures, materials and techniques used by fleet maintenance personnel to combat the problems associated with the corrosive environment. The ultimate goal of the Design Guide is directed toward developing an awareness in the design engineering phase and providing some preventive design techniques. This includes consideration for maintenance materials and procedures, required to achieve more C/F/M resistant designs for avionic equipment that must survive and operate in the hostile operational and maintenance environment.
Various design characteristics described in this Design Guide are based on actual examples in fleet aircraft and hardware. The specific identifications are not noted, although many of the poor design features are not, unfortunately, unique to any one design contractor or equipment.