The experience of auditing software for safety critical railway signalling equipment

Abstract

The experience of carrying out Audit of two versions of Software for a Railway Signalling equipment, called the Universal Fail Safe Block Interface (UFSBI), being developed by two vendors is described. For the users and the developers, this had been the first exposure to formal development of safety critical software. The auditors were academics with IV&V experience for only aerospace software and no prior experience with railway signalling system. Prototypes of UFSBI had been operating before the auditors were formally brought in, but a full life cycle audit was undertaken due to safety criticality of the system as per the European CENELEC standard, desired to be adopted by the users. In the absence of local precedence, new paradigms of interaction had to be evolved and the role of the auditors, expanded to also include mentoring and facilitation. Initial scepticism and conflicting expectations from software audit gradually became a participatory learning activity for all the involved parties.