Originally Posted by
ASI211
If it is a flight operated under 14 CFR Part 135, I'd say no. Reference 14 CFR § 135.113, passenger occupancy of pilot seat and 135.115, manipulation of controls.
135.113 says that no operator can operate a flight outside of that specified limitation however, it does not imply that an occupant in the plane operating the radio constitutes a violation on behalf of that occupant.
Since the radio isn't a flight control, I don't think 135.115 is applicable, and even if it were, it states that no PIC can allow such an action which doesn't imply that the occupant is violating any rule.
I do see a grey area where it would appear that the occupant was not receiving flight instruction if the operator and PIC are forbidden to allow it however, that would open the door to imposing violations upon students where the instructor was operating outside his own requirements such as if the instructors certificate had expired or whose medical wasn't in order. It would then become a burden upon the student to validate the instructors credentials and currency status.