737 Volcanic ash bleed demand

[nick14]

Hello all,

I am after some technical advice on the 737NG Volcanic Ash checklist.

There are several references to increasing bleed demand thereby increasing surge/stall margins (packs in high,wing and engine anti-ice on). My question is how does the increase in bleed demand increase the surge margins?

Not being an engine man I have been searching for an answer as our company sim training is focusing on this scenario.

Thanks