Normally a crew would only select WAI on when the LE flaps are up. Auto mode simply imitates this behaviour. The real question is why does Boeing allow you to open the valves even when the LE flaps are down, as is possible on aircraft with auto WAI by placing the switch in ON. Other than their basic philosophy of allowing automatic systems to always be able to be overridden, it is useful when one valve has stuck open to avoid asymmetrical bleed demands, or when you've flown into a volcanic ash cloud, where you want to keep the air flowing through the engines as much as possible. BTW in the last nine years I've seen the auto WAI come on once .
Last edited by Long Haul; 10th January 2003 at 07:27.