Diagnostics can now be provided for aircraft hydraulic systems to determine continuously the on-condition health of operating components such as pumps, servovalves, and filters. Multi critical parameter data such as FLOW, TEMPERATURE and DIFFERENTIAL PRESSURE can be obtained to indicate internal wear and degradation of operating component surfaces before malfunction and failure occur. The data can be obtained during normal system operation and supplied directly to an on-board computer to be compared to maximum allowable component parameter limits for diagnosis of the health of the component and to indicate maintenance action required. The SENSORS monitoring FLOW, TEMPERATURE, and DIFFERENTIAL PRESSURE and their applications and use in the system are described. Signal conditioning interface modules are also described. Maintenance cost savings and reduced maintenance skill level are made possible by the new SENSORS. Additional benefits of reduced logistic support and reduced downtime will justify application of this new SENSOR technology.