This publication will be limited to a discussion of liquid and particulate contaminants which enter the aircraft through the environmental control system (ECS). Gaseous contaminants such as ozone, fuel vapors, sulphates, etc., are not covered in this AIR. It will cover all contamination sources which interface with ECS, and the effects of this contamination on equipment. Methods of control will be limited to the equipment and interfacing ducting which normally falls within the responsibility of the ECS designer. The purpose of this Aerospace Information Report (AIR) is to categorize sources of Environmental Control System contaminants, define the effects of these contaminants on occupants and equipment, and outline design features that can be used to control contamination in aircraft systems.