Complex sentence: The aircraft flight manual said not to relay on airframe visual icing cues before turning engine anti-ice on, and the consequences of using an engine anti-ice until build up is visible from the cockpit may result in severe engine damage.
Split into simpler sentences: The aircraft flight manual said not to relay on airframe visual icing cues before turning engine anti-ice on. It states that the consequences of not using an engine anti-ice until build up was visible from the cockpit might result in severe engine damage.