This document gives guidelines for identifying:a) The typical architectures of touch-down bearing systems to show which components are likely to comprise such systems and which functions these components provide;NOTE Touch-down bearings are also known as “backup bearings”, “auxiliary bearings”, “catcher bearings” or “landing bearings”. Within this document, the term “touch-down bearings” is used exclusively as defined in ISO 14839-1.b) The functional requirements for touch-down bearing systems so that clear performance targets can be set;c) Elements to be considered in the design of the dynamic system such that rotordynamic performance can be optimized, both for touch-down bearings and active magnetic bearings (AMBs);d) The environmental factors that have significant impact on touch-down bearing system performance allowing optimization of overall machine design;e) The AMB operational conditions that can give rise to contact within the touch-down bearing system so that such events can be considered as part of an overall machine design. It also considers failure modes within the AMB system that can give rise to a contact event. This ensures that the specification of the touch-down bearings covers all operational requirements;f) The most commonly encountered touch-down bearing failure modes and typical mechanisms for managing these events;g) Typical elements of a design process for touch-down bearing systems including the specification of load requirements, the sizing process, the analytical and simulation methods employed for design validation;h) The parameters to be taken into account when designing a touch-down bearing system acceptance test programme including the test conditions to be specified and the associated instrumentation to be used to ensure successful test execution;i) The condition monitoring and inspection methods that allow the status of in-service touch-down bearings to be evaluated and when necessary identifying the corrective actions to be taken;j) The factors to be considered when designing the maintenance regime for a touch-down bearing system including the actions to be taken after specified events have occurred together with any actions to be performed on a regular basis;k) The factors to be considered regarding other life cycle topics (e.g. obsolescence management, de-commissioning and disposal).