© Infrastructure Working Group, International Council On Systems Engineering INCOSE-PI-2015-005-1.0, Version 1.0. Authored by Manoj Keswani.

Conversely, the ability to restore a failed system is dependent on the ease with which a system can be maintained. This is dependent on how the system was designed and built so that failed components can be easily replaced (i.e. has a low mean time to repair) and how often and how well periodic maintenance of the system is carried out to ensure predictable failure is minimized (i.e. an optimized preventative maintenance regime). Maintainability therefore is a combination of good design and build practice as well as processes and procedures through the operations and maintenance lifecycle that minimize the chance of any failure or manage the risk of failure proactively Once reliability and maintainability are controlled through good operations and maintenance practice, then the availability (or ‘uptime’) of a system improves. Balancing the availability of the system with the time required to take the system off-line to carry out essential maintenance can affect how safe the system solution is deemed to be. If operational practice is driven too hard by keeping availability high, then there is a risk that lack of sufficient maintenance will lead to failure and reduce the overall safety of the railway. In addition, there are significant Human Factors (HF) considerations that need to be taken into account when planning operations and maintenance activities as they have a significant impact on the performance and safety of the railway system. Specialty engineering disciplines that particularly have expertise and experience in the areas below need to work with the other technical disciplines to develop an integrated approach to the engineering of a railway system: • Safety, hazard and risk analysis