There are frequent attempts to compare the reliability of naval avionic equipment to its equivalent in commercial airliners. In some cases it may be identical equipment, yet airline use invariably results in much higher reliability. A major reason of this reliability differential can be attributed to the gross differences in operating conditions. Avionic equipment is designed primarily to perform its operational function with minimal concern for what happens during static periods. These static periods constitute some 90% of the chronological life of installed Navy equipment and are a significant factor in the high corrosion problem related to this avionic equipment.
FLIGHT HOURS PER MONTH
Many carrier aircraft average approximately 350 to 400 flight hours per year, or slightly over one flight hour per day. Commercial airliners, on the other hand, average approximately ten hours per day. Corrosion is a process that is most active during non-operating periods because of the lack of heat from operating equipment (which tends to drive off or minimize moisture when the power is on). Also, seals are unpressurized, and water separators and air conditioners are not operating. Thus, even if the naval and commercial physical environments were the same-which they are not-the airliner equipment is exposed to the most corrosive (static) conditions approximately one-tenth as much as that in the naval aircraft.
LOW LEVEL FLIGHT OVER WATER
During low-level overwater ASW (Anti-Submarine Warfare) operations, considerable saline moisture is inducted into the aircraft because of the fine ocean spray prevalent in the lower altitudes. Items such as wiring harnesses, connectors, antennas, waveguides, switches, bonding and grounding straps, racks, etc., become susceptible to this induced moisture.
In the case of a helicopter hovering at low altitude, the aircraft literally can disappear from view in a cloud of sea spray. The voluminous induction of the salt water spray into vents and cooling air ducts is far beyond the capacity of any water separation system. Also, a common operational mission for helicopters involves picking up swimmers, UDT ( Underwater Demolition Team), or other personnel from the ocean. Such operations obviously result in the introduction of copious amounts of sea water into the cabin. This water can run along wire harnesses, cables, waveguides, hydraulic lines, etc., to avionic equipment before it drains into the bilge area where it penetrates belly mounted antennas and other vulnerable equipment.