I never flew the classic, so I have no clue. Saw this on fb:
“On long range sectors, where fuel could be critical, and dodgy weather they (a kangaroo airline) would fly single pac, the air became very stuffy, it was hard to breathe when working, a quick visit to the flight deck confirmed it, only one pac running, they weren't supposed to do it, but they did.”
Could it fly with one pack ops?