scope:

This applies to Bakerloo, Victoria, Central & Waterloo and City, District, Met & H&C, Jubilee, Northern and Piccadilly Lines on LU signals

This TANC Guidance is used for all safety critical assets where a non-compliance would affect the safety of the operational railway.

This guidance is applicable to planned Routine Maintenance, Annual Assurance Testing and Routine Change maintenance activities across all LU signalling systems.

Under normal operation of Transmission Based Train Control (TBTC) / Communication Based Train Control (CBTC) the TANC process will not apply to the assets that form part of these system where the design of the system provides diverse protection, that inhibits potential incorrect operations or modes of wrong side failures. The exception to this would be all point systems.

However, if the TBTC and CBTC systems have to operate in degraded mode for more than 24 hours then the TANC process would apply to any back log secondary assets e.g., Axle Counters, Signals head, etc. in consultation with Technical Authority to agree on required mitigations and controls.

Purpose

This guidance explains the way in which Signals Asset Performance Delivery (APD) provides validated assurance of adherence to the Engineering Standard S1642, Temporary Approved Non-Compliance (TANC). This guidance describes the steps that need to be taken to permit any non-compliant signals assets to temporarily remain in service and provides the appropriate compliance documentation. The purpose of this procedure is to ensure that any non - compliances with signals asset maintenance requirements or non-compliance to standards asset configuration is managed in a consistent and controlled manner.