This document has been declared "Stabilized" and will no longer be subjected to periodic reviews for currency. Users are responsible for verifying references and continued suitability or technical requirements. New technology may exist. This SAE Aerospace Information Report (AIR) discusses the impact of the ISO Test Dusts, chosen as replacement contaminants for the Arizona Test Dusts (AC Test Dusts), and the ISO calibration procedure ISO 11171 for automatic particle counters, which replaces the calibration procedure ISO 4402 (1991), on laboratory performance of filter elements utilized in aerospace lubrication, hydraulic and fuel systems, and fluid cleanliness levels determined with automatic particle counters.