View Full Version : B737 engine and wing anti-ice at the gate?

28th Apr 2004, 02:01

If you are at the gate, APU power, and you select the wing or engine anti-ice on the APU on, the bleed pressure drops significantly...the air is going somewhere.

Is wing and engine anti-ice effective at the gate while on APU power? If not, where is all the air going?


28th Apr 2004, 19:08
Air for engine antiice comes only from the engines, but you can warm the wings using the APU, although total nonsense, at the gate.

What's the big mystery?

30th Apr 2004, 22:15
As LEM stated, Engine Anti-Ice can only be supplied by the Engines. The APU is not designed to supply air for the WAI, as the Wing Anti-Ice requires alot of air....hence the huge pressure drop.

30th Apr 2004, 22:28
Isn't WAI available only in flight?

30th Apr 2004, 22:45
No, WAI is available on the ground. It is limited by Ground Thermal switches and throttle position. Throttle position past I believe 55 degrees will shut down WAI on the ground. It can be reset inflight.

4th May 2004, 06:30
As far as I know, WAI is only available in flight. Could you be mixing up High Bleed and Low Bleed?

4th May 2004, 12:11
No, unless this is something that can be an option...then I am sure that I am correct.

4th May 2004, 17:06
B73567AMT is correct.

However, there are dozens of variants of our beloved toy...

In our fleet we have both types, one "normal", and one modified on which you have to keep the switch in the GROUND TEST position to open on the ground.

4th May 2004, 19:01
On our -300 and NG aircraft the following applies:

Wing anti ice can be used on the ground, it is selected during the after start checks if required.

However when the aircraft rotates the wing anti ice automatically shuts off, this is so that in the unlikely event of an engine failure the WAI doesn't take any power away from the engine when it is critical. It can be reselected at a later stage.

Hope that clears it up.

6th May 2004, 13:56
more variants:

Ours (-4/500) close the WAI valve when thrust levers are moved through the TKOF warning position (lights go bright blue for switch/valve disagreement). At lift-off, only the switch trips to (correct) OFF position.

Precisely as described in VOL2 pg. 3.20.6.

This is also performance wise should engine fail between V1 and Vr. In case you need WAI on ground, it is most likely that the runway will be at least wet so there will be some time to go from V1 to lift-off. Our engines are not restricted to failing when airborne only. :uhoh:

Can be reselected any time when the AC is in air mode (click at liftoff), i.e. immediately. However should I really NEED the WAI after take-off, I'd decide not to fly at all.