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Background The signalling system contractor Alstom-Thales DUAT Joint Venture (ATDJV) has been carrying out tests of the new signalling system during non-traffic hours at different sections of the Tsuen Wan Line by phases since late 2016. The ATDJV commenced full-line train tests in early 2018, and had subsequently completed the tests on site, which lasted for more than two years, in Feb 2019 On 16 Feb 2019, the MTRCL commenced a series of drills and exercises before putting the new signalling system into revenue service. Analysis According to our investigation findings, the cause of the incident was a programming error introduced during software rectification of the new signalling system at the design and development stage. This programming error caused a failure to re-create the data of the crossover track at the Central Station after switch-over from the primary zone controller (ZC) to the warm-standby tertiary ZC. Hence the Automatic Train Protection (ATP) system co

Background The new signalling system of TWL developed by the contractor is divided into two control zones. In each control zone, it comprises three signalling zone controller computers, namely the Primary("A), Hot-standby("B"), and Warm-standby("C") computers. Computers A, B and C are of the same hardware and loaded with common software. They are configured to perform functions of Computer A, B and C through a hardware identity plug, which allows the common software to process dynamic data among the three computers correspondingly. Computer C only receives selected dynamic data from Computers A/B so as to avoid common mode failure. This configuration aims to improve system availability and service recovery through high resilience Computer C is housed at a different station which enhances system security through access control and diverse power supply. The Panel agrees the warm-standby arrangement is novel in contractor's signalling system app