This SAE Aerospace Recommended Practice (ARP) establishes the factors which should be considered in the design and installation of a hydraulic system fitted to a commercial transport rotorcraft.The purpose of this document is to provide in one document information and guidelines to the designers of commercial transport rotorcraft hydraulic systems and components including: a. reliability and maintainability requirements; b. federal aviation regulations (FAR)/joint airworthiness requirements (JAR) that are applicable to hydraulic systems; and c. design and installation practices.This document applies to the hydraulic systems installed into commercial transport rotorcraft which are designed to comply with FAR and/or JAR 29 regulations.