Originally Posted by
Too Few Stripes
whether pack switches should be off or not during a turnaround
This is airline and type dependent, thus your SOP.
Some operators in transit checks turn them OFF, to enable Ground Air Source (LP) to be connected by default.
Other operators in transit checks turn leave them AUTO, enabling APU Conditioning when APU BLEED is selected ON, yet switching them OFF immediately prior to engine start, not using them prior to such event when OAT is above or below a certain minimum or maximum value (Never understood the reason why SOPs would dictate this method of using them, but anyhow...).
Either case is/can be correct,d spending on your type of operation and associated SOPs.
Furthermore, there is a potential difference between NG's with multiple zones (800/900) and the single zone cabins (600/700), again SOPs define their use.
There are many way str skin a cat.
In this case there is no requirement for either position, merely a defined SOP advising you what to do in your type of operation.
Remember an operator generally operating in moderate altitudes to large well equipped airports with APU restrictions and Ground Conditioned Air Sources will have a different view as another operator flying in areas with mostly isolated stands and higher then average temperatures.