The wind ISOL Valve switch and BLEED AIR SOURCE selector will only have an effect if the bleed valves control selector is placed in which position?

• A. AUTO
• B. OFF
• C. MANUAL
• D. LOCAL

Answer: (C)

Understanding how the bleed air system is controlled reveals why manual is required for those switches to have an effect. The system has automatic sequencing that manages valve positions and bleed-air source selection to meet the aircraft’s air conditioning, pressurization, and de-icing needs. Some controls, like the Wind ISOL valve switch and the bleed-air source selector, are only capable of altering the actual valves and source when you override the automatic logic by selecting manual mode. In automatic mode, the system automatically positions the bleed valves and chooses the bleed source, so manual switches can’t change them. Local or other modes may also rely on automatic control and therefore won’t respond to manual overrides in the same way. So, to directly influence those components, the bleed valves control selector must be set to manual.