Hi atuk -
your quote:
Q1..To avoid backpressure to apu bleed from eng bleed. Its boeing Non-AFM operational limitation that Apu bleed valve must be closed if eng bleed valve open.
is not quite correct:
If what you say is true, you wouldn't be able to start your engines with the APU bleed supply. I'm sure you meant to say that with both the engine and APU bleed valve open (DUAL BLEED light on), the respective engine must remain at idle.
Cheers, FD
