Which alternate cleaning method involves completely immersing the affected equipment in a 55-gallon drum of water-displacing corrosion preventive compound?

The water-displacing method is significant in avionics corrosion control as it involves immersing the affected equipment in a corrosion preventive compound that displaces moisture. This immersion helps to protect metal surfaces from oxidation and corrosion by forming a protective layer. The use of a 55-gallon drum suggests a comprehensive approach to soaking equipment that is heavily affected by corrosion.

This method is particularly effective in areas that are difficult to reach with other cleaning techniques, ensuring that all surfaces are adequately treated. It's designed to not only clean but also leave a protective coating, which is essential in maintaining the integrity and functionality of avionics components.

Other methods mentioned do not utilize immersion in the same way. The vacuum method focuses on removing debris and contaminants without the use of liquids. Foaming methods typically involve applying a cleaning foam to surfaces rather than submerging the entire component in a solution. Meanwhile, ultrasonic cleaning uses high-frequency sound waves in a liquid solution to agitate particles and contaminants away from surfaces, which does not involve total immersion in a corrosion preventive compound as emphasized in the water-displacing method.