What must be established before allowing certain mixed signal aspects with a malfunctioning ASC apparatus?

Establishing an absolute block is essential before permitting certain mixed signal aspects when an Automatic Speed Control (ASC) apparatus is malfunctioning. An absolute block serves as a safety measure ensuring that no train can enter that section of track while a conflicting signal is displayed, thus preventing potential accidents. By requiring an absolute block, train operations can be controlled more safely, ensuring that trains do not proceed past a signal that may not be functioning properly. This control mechanism is fundamental in maintaining safety and preventing collisions or other incidents on the rail network.

While other options might concern the management of signals and operational procedures in various contexts, they do not provide the same level of safety assurance as an absolute block when addressing issues caused by malfunctioning ASC apparatus. The absolute block ensures clarity in system status and protects against the risks posed by mixed signals.