Delaying the use of engine anti-ice until ice buildup is visible may:

Delaying the use of engine anti-ice until ice buildup is visible can indeed result in severe engine damage and/or flameout. In conditions where ice can accumulate on engine components, failing to activate the anti-ice systems in a timely manner allows ice to form and potentially disrupt airflow or create blockages, which can significantly affect engine performance. The presence of ice can lead to reduced thrust and increased chances of stalling the engine, leading to a flameout. This is particularly critical in aircraft operations where maintaining engine reliability is vital for safety.

The correct answer underscores the importance of proactive measures in ice-prone environments, highlighting that waiting until ice buildup is observable can have dire consequences, making it essential for pilots to monitor conditions and activate anti-ice systems as required, before visible ice accumulation occurs.