B737
 

Why does wing anti ice on increase approach minima? If due to increased idle thrust, wouldn't that allow lower minima?

Outboard section of the wing has no thermal anti-ice and cannot be guaranteed to be ice free even when using wing anti-ice.

Edit:

Didn't read question correctly. Thought was asking about minimum speed (ie Vref ICE) as opposed to minima.

Note to self: RTFQ

Nothing to do with which bits of the wing are protected, it is to do with the fact that it uses bleed air from the engines to heat the leading edges, thus that reduces available climb performance, hence if you need to go around to achieve a limiting climb gradient you will have to start from higher up....or possibly fail to achieve said gradient.

PP

Then what happends after you turn wing a/i off? Wouldn't the engine bleed air be "back in" the engine? The plate state that if wing a/i has been on during the flight, weights vs minima will be affected..

Boeing documentation does not mention amended instrument approach minima when using wing anti-icing - suggesting it is of no statistical significence?

Pilot Pete above has hit the nail on the head. Best example is to look at the go-around climb gradient graph, it shows you the actual increment and what effect it has - I believe it is only applicable for minima below CAT 1 i.e. 200ft. Obviously you might want to go to the pub instead :ok:

Check me on this. Wing A/I does not affect the aircraft approach performance singificantly. It WILL affect the MISSED approach CLIMB gradient. At most places the required minimum missed approach gradient is so shallow that with wing A/I on or off the resulting actual gradient is way above the minimum.

Variable approach minima is in use where any kind of thermal A/I derrived from engine bleed source is considered. Chambery LFLB is one example.

Mr L