Holding a licence.
So, if you don't hold a valid license, then you could legally fly any plane (even the big iron) as not having a license does not make you part of the flight crew? Are you guys for real?
Let me spell it out for you: manipulating the flight controls means acting as part of the flight crew, and to do that
legally regulations clearly and unambiguously state that you must hold a valid and appropriate license.
I'm outta here, this is getting too silly and quite pointless.