Wing anti ice logic

[lj_dekker]

Hi,

When WAI switches are placed in ON longer than 5 seconds in flight, the stall warning logic adjusts stick shaker and minimum maneuvering speeds to icing condition requirements. Recently I spoke with a test pilot who said he sometimes placed the WAI switches in ON before take off so he would be on the "safe side" with stall speeds etc.

My question: When this is done IN FLIGHT the stick shaker and min maneuver speeds will be adjusted, and remain so for the rest of the flight. But are these speeds also adjusted for the following flight when the WAI switches are placed ON BEFORE take off? Because when you select them in on, they will tripp off at lift off.

I was just wondering if he was right .

[pitrsv]

Maneuver speed should be changed everytime when WTAI switch is placed to ON position but.....
There is WTAI logic - If the throttle levers are advanced more than 60°,WTAI switch is automatically tripped off on the ground to preserve engine power during T/O. WTAI switch is also tripped off if the overtemperature condition occured.

[lj_dekker]

So are the adjusted stick shaker and maneuvring speeds still active after a/c goes in take off when WAI was selected before take off?

[pitrsv]

These speeds are active provided WTAI switch in ON position. During T/O the WTAI switch automatically trips to OFF,so speeds are not active. If pilots switch on WTAI after T/O,speeds are active again.

[lj_dekker]

I know the WAI switch trips off at take off, so there will be no hot air blowing throught the vents in the slats. But amm states then when WAI is used speeds are active for remainder of the flight, even when WAI is not used anymore. Aren't you confused with Engine Anti Ice? When EAI is used speeds are also adjusted but go back to normal when switches are placed back in off.

So if you place the WAI switch momentarily in ON before take off, are the speeds adjusted for the rest of the flight?

[Timthom]

Stick Shaker and Minimum Manuvering Speed are only adjusted if the WTAI system is placed to ON when the aircraft is in the air mode (and FMC displayed VREF is not adjusted at all).

I tried several different NG aircraft and setting the WTAI switch to ON with the aircraft in GND mode caused no change in SMYD computed speeds. This does make sense as why would you adjust the speeds on the ground for a system designed to shut down on takeoff?