"If you had both engine bleed switches OFF, then you would want the packs to supply a larger volume of air since the APU cannot supply as much as the engine bleed air can."
Thanks, B73567AMT.
I guess that's one way of looking at it. I think I am more used to aircraft where the bleed air is used more extensively, such as for ADP's, Reversers, NAI, etc. In the air, it looks like the APU on a 737 is under less stress than other aircraft (if there is no air coming from the engines): It looks like the major loads for the 737 are limited to WAI and Aircon (or is there any way APU bleed can be used for Nacelle Anti-Ice?). I suppose engine start is another use.
"Why would you switch off the Engine Bleed switches anyway?
Dual Bleed problems (not Dual bleed light)?"
I was wondering that myself. Is there a procedure for smoke in the cockpit which involves shutting off both sources of engine bleed air?
Re GR's post (which mysteriously disappeared)....
"The only person normally capable of answering this type of question is you, and as you dont the answer I very much doubt anyone else does !"
Unfortunately, GR, I am very much the amateur when in comes to 737's... I think anyone can sound intelligent though, when they have the BMM, the FIM, the Schematics and the Wiring Diagrams in front of them...
... not forgetting fellow engineers and unlimited internet resources!
Cheers and thanks!
Q.