Starter generator reset. Cross generator start.

[85discus]

Hi,
Why is the starter generator reset before turning it ON.
What is cross generator start and why is it prohibited except in an emergency.
(This refers to a Dash 6 with PT6A-27)
Thanks!

[KRviator]

A Cross generator start usually refers to using the output of the starter generator to power the opposing starter, rather than recharging the battery first and then using the battery to crank the second engine.

it tends to be particularly hard on the generator, so many types have some kind of limitation or prohibition on it.

[westhawk]

Similar limitations exist for the King Air 90, Lear series and probably several more "classic" turbine aircraft types... In the BE9L, the gen on the operating engine must be turned OFF while starting the second engine until reaching 12% N1, then it may be turned back ON for the remainder of the start cycle. If the second engine start is initiated with the operating engine gen ON, (oops!) a current limiter may fry (open) to break the connection to the operating gen bus to protect the operating gen. Now mx has some work. The gens are rated at 250 amps and the initial current draw from the starter can be over 1000 amps. Many airplane types don't have this limitation because their electrical systems were designed differently. On one type I used to fly, the schoolhouse mantra was "all starts are battery starts, but may be generator assisted".

Anyway, I was only recently checked out on the King Air, so I'm still working hard to ingrain this "new normal" start procedure. I hope I don't forget!