This paper was published in IRSE NEWS June 2017. It was originally presented at the Australasian Section AGM and Technical Conference held in March 2017.

The paper explores the challenges associated with the assessment and type approval (also known as product acceptance) of systems and equipment for railway applications. The type approval process generally requires a supplier to provide an information pack (e.g. as recommended in AS 7702:2014) demonstrating adequate reliability and safety. The rail organisation will then assess whether the product is suitable for use on its infrastructure. A key component of type approval is evidence of a product’s or system’s Reliability, Availability, Maintainability and Safety (RAMS).

The impetus for this paper has been the misapplication of RAMS for electronic and programmable electronic systems and the many requests for RAMS information for mechanical or electromechanical equipment that are phrased in terms only appropriate to electronic or programmable electronic systems.

The objective of this paper is to encourage use of appropriate and meaningful indicators, and how they are meaningfully used, in the type approval and general assessment of the RAMS of mechanical and electromechanical railway signalling equipment. Meaningful indicators are essential to ensure safety "So Far As Is Reasonably Practical" (SFAIRP), as required by the national rail regulator.

The paper specifically looks at the application of RAMS parameters, Mean Time Between Failure (MTBF) and Safety Integrity Levels (SIL) for mechanically based equipment and how they might be used for type approval of such equipment.

The paper explores topics such as the "bath tub" curve, infant mortality, wear out, and the differences between the assessment of electromechanical equipment and electronic/software based equipment.