Jaba,
Sorry, maybe I should have been more expansive.
We have had a number of serious incidents with Alternators turned off, contrary to SOPs, and then not turned on at the next engine start.
Result, on a good day, just depleted batteries and complete radio failure, on a bad day, loss of the aeroplane, and another Coroner's Inquest.
Hence ----
what does the manual say.??
From the Cessna 310R POH. Pre Start check list requires Alternators ON. The only time it is different is with Ground Power. For GPU starts Battery and Alternator must be OFF prior to plugging in and they stay that way until after engines are started and GPU plug removed.
And the POH is the AFM, see CAR 138.
PLovett, maybe there us some truth in who writes AFMs (POH) as a result of court cases, but whether you like it or not, you are stuck with it. In reality, there is the collected experience of the manufacturer in a POH/AFM --- which is a document you are legally required to observe ( unless you are a CASA FOI, of course, then you have a delegated exemption from the laws of physics and aerodynamic, as well as the aviation law) on pain of potentially severe penalties.
Tootle pip!!