The purpose of this Aerospace Information Report (AIR) is to provide information and guidance for the selection and use of oil system monitoring devices and methods. This AIR is intended to be used as a technical guide. It is not intended to be used as a legal document or standard. The scope of this document is limited to those inspection and analysis methods and devices which can be considered appropriate for routine maintenance. In agreement with industry usage, wear particle size ranges are given in μm (1 μm = 10^-3 millimeter = 10^-6 meter). Other dimensions are given in millimeters, with inches in parenthesis.