Wing Anti Ice Valve On the ground, positioning the WING ANTI ICE switch ON opens both control valves if thrust on both engines is below the setting for takeoff warning activation and the temperature inside both wing distribution ducts is less than the thermal switch activation temperature. Both valves close if either engine thrust is above the takeoff warning setting or either temperature sensor senses a duct over-temperature. The valves automatically reopen if thrust on both engines is reduced and both temperature sensors are cool. With the air/ground sensor in the ground mode and the WING ANTI ICE switch ON, the switch remains in the ON position regardless of control valve position. The WING ANTI ICE switch automatically trips OFF at lift off when the air/ground sensor goes to the air mode.