1)
A 3rd Generator (APU GEN), driven directly by the APU and producing the same output as each main engine generator, can replace either or both main engine generators at any time.
The APU can be started and used for electrics up to max operating Alt, (Air supply 1 pack below 22,000, & 2 packs below 20,000). If you are down to batteries the APU start limit is 25,000'
2) Don't know - but the main doors have red indicators in the windows to indicate that the aircraft is still pressurised.
T'bug
