Manning Positions with Trainees
 

I seem to remember seeing some guidance/instruction limiting the number of trainee controllers that can be manning positions at the same time, but can't remember where. We will shortly have a situation where Tower and Approach will both be manned by trainees simultaneously. Can anyone point me in the direction of any guidance as to whether this is illegal/inadvisable/at UTO's or OJTI's discretion?

Happens regularly at my unit

Why would it be illegal and/or inadviseable? You still have a licensed controller in each position who has the ability to take control of the situation at any time (and arguable as an OJT they should have executive control at all times anyway.)

Of course, if an OJT is unhappy with any aspect of traning at any time they should be able to stop training and control 'solo'.

Also happens regularly with us, but we do take into account the progress of the individual before intentionally rostering as such.
If there's any doubt that one would hinder the other, it doesn't happen, alternatively, as Aerotech says, the OJTI in an individual position has the final say.

This is down to local SOPs. For example our SOP says we can't have simultaneous trainings on GND and TWR positions, same goes for APP sectors (reason being it might be detrimental for the flow of traffic, not that it it unsafe). On the other hand, simultaneous OJT sessions are carried out on ACC sectors all the time.