PENKO, Wirelock, thank you. I think putting 2+2 together, we may have good clues to an answer. First, two quotes:
Originally Posted by PENKO
But anyway, I just found the closest thing to an answer in FCOM 3.2.29 (pump low pressure)
Quote:
Note : If yellow system is affected, the yellow elec pump may be used
, and,
Originally Posted by Wirelock
for dual engine failure you still would have apu available assuming you still have fuel.
We wouldn't want to start the APU in a dual engine failure because it would use up battery power, (I believe there is a caution regarding this in the QRH dual engine failure checklist). Using
PENKO's quote, the pump
can be used (ECAM drill for
HYD G+Y SYS LO
PR requires Yellow electrical pump ON if ENG 2 PUMP LO
PR) but
Wirelock's quote is a clue to why the Yellow pump isn't turned on. In a dual engine failure, the Blue system is hydraulically powered by the RAT but the yellow pump is electric (AC2) and the Emergency Generator (blue hyd sys) only powers the AC and DC ESS Busses.
In the QRH drill for dual engine failure, when on approach the flap lever is selected to "3" but the note indicates that only the slats will extend and they will be very slow. I think the lever is placed in the '3' posiiton to satisfy a number of computer inputs which use the flap lever position for PFD indications, GPWS, etc, but this is an educated guess only. If anyone knows the exact reason, (again, the book doesn't tell us), please let us know!