When Software Goes Wrong - A City Metro System

In this fifth podcast about the impact of software failures on railway asset safety, I talk with Dr Emma Taylor about the causes behind an accident that happened during testing on a city metro system. In this episode we highlight some of the failures as they relate to the stages in the V-model that is, or should be, applied to the software development lifecycle. A set of processes that is particularly important for verification and validation during the development, testing and implementation of complex software-based systems.  This is not a definitive assessment of the incident, just an analysis to increase understanding of complex software-based systems and their implementation.

One of the aims of this podcast is to share learning with the wider industry to support a wide range of stakeholders including train manufacturers and owners.

Listen to the podcast

Topics in this episode include:

• Emma describes the importance of using the V-model to verify and validate the integrity of safety-critical software systems [2:04]
• Emma describes the signalling failure incident and the major changes that were being tested [3:10]
• Emma talks about the system definition step in the V-model, and her opinion of some assumptions made about the dependability of the core software [4:43]
• Emma explains latent software faults [5:16]
• Emma talks about the need for risk assessment, identification of hazards, and the design of software systems to avoid the identified hazards [5:50]
• Emma gives some personal thoughts as to why a data synchronization issue might have been missed [7:25]
• Emma talks about the practical stages of software development, the 'apportionment of system requirements' and the importance of recording changes in design [8:15]
• Emma talks about the failure of data copying between systems and the related process documentation [9:20]
• Emma talks about the testing part of manufacture, the verification and validation, throughout the lifecycle [10:22]
• Emma describes the role of third-party, independent assessors in the development process [11:38]
• Close [14:36]

Resources mentioned in this episode:

• The V-model on Geeks for Geeks.org
• The V-model for humans on Wikipedia
• Loss of safety critical signalling data on the Cambrian Coast line, 20 October 2017 
• The digital bits of a system podcast.

Other related resources:

• LHSBR Infrastructure Asset Integrity section
• LHSBR Rolling Stock Asset Integrity section.