b737ng pressurisation
hello gotabefun,
in order to deconfuse, let's get back to the kiss principle: keep it simple, st*pid.
first of all, boeing qrh does not consider multiple failures at the same time, which doesn't mean they can't occur of course.
in your example the right pack = u/s. with the right pack switch off, the isolation valve, in the auto position, will be open.
the isolation switch logic( in auto), looks only to the 4 corner SWITCH position, eg.pack valves & bleed valves.if any corner switch is selected off, the isolation valve, in auto, will be open. ok, so here you fly with 2 bleed sources for one pack, which is acceptable. (1 bleed source for 2 packs, in flight, would not).
now, having a bad day, comes the left engine failure. you follow the qrh faithfully, which amongst other things, asks you to switch the pack on the affected(LH) side off.
if you do that, pressurisation is lost.
but here is a typical situation, where common sense & system knowledge come into play. the qrh gives you a hint in the brackets on the next sentence.
QRH:
PACK SWITCH (affected side)..................OFF
[causes operating pack to regulate to high flow in flight with flaps up]
in your example the "operating" pack is the right pack. but is not available.
so in this case, it is best to leave the LH pack switch on, fed by engine n°2 through the isolation valve in( auto )open.
if you are unshure of the isolation valve logic in auto position, you can always ask yourself:" do i want the isolation valve to be open or not?" & switch it open or close manually.
as for the apu, you will use it to substite the generator n°1.
apu bleed & electrical limitations:
from sealevel to 10000feet: apu can supply bleedair & electrics.
from 10000ft to 17000ft: apu can supply bleedair OR electrics.
above 17000ft to 41000ft(structural ceiling): apu can only supply electrics.
hope this brings some light in the darkness & yes, please land at the first suitable airfield.